Kilauea releases mafic magma, and the temperature at eruption is about 2,140 degrees Fahrenheit.
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Orange is hotter, in the intermediate range, and yellow is hotter still, in the mafic range.
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This requires the assumption of a mafic crust; you can read our discussion of the early Earth's composition here.
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That doesn't imply that the ancient earth had oceans, since the other planets have mafic crusts but no oceans.
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It looked to the geologists as though the rocks had been formed through a partial melting of other older basalt-like "mafic" rocks.
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Then, they ran computer meteorite impact simulations of a 10-kilometer-wide meteorite hitting a mafic crust at 12 to 17 kilometers per second.
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The mafic or basaltic magma, which is only about 45 to 55 percent silicon dioxide, can be a very hot 1,832 to 2,192 degrees Fahrenheit.
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Generally, folks think Hadean Earth might have been a hellish world that looked a lot like our rocky neighbor planets Mars or Venus, which have mafic crusts with no plate tectonics.
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Instead, if the Earth started out with mainly mafic oceanic crust, it begs the question of why we have so much felsic continental crust today, said Ming Tang, geochemist at Rice University.
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It turns out, the rocks found by O'Neil's team carried a signature indicating they had been formed from a mafic source around four billion years ago, and then were recycled before finishing up as part of the Canadian Shield.
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O'Neil and his colleagues used these signatures to determine whether their Canadian shield rocks originated from a "felsic" source, a granite-type rock typical of crust found on land, or a "mafic" source, a more basalt-like rock found in the crust of the seafloor.
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The deposits are typically associated with bimodal sequences (sequences with subequal percentages of mafic and felsic rocks - e.g., Noranda or Kuroko), felsic and sediment-rich environments (e.g., Bathurst), mafic and sediment- rich environments (e.g., Besshi or Windy Craggy), or mafic-dominated settings (e.g.
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Ultramafic and mafic rocks and their metamorphosed equivalents could be observed in Eastern Iran (Fariman area), Taknar Series, Gorgan schists, and Shanderman mafic/ultramafic metamorphic series.
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There were granitic intrusions and mafic dyke intrusions 2.35–1.92 billion years ago. The mafic dykes were later metamorphosed as mafic granulites and amphibolites. Eventually, the whole ocean sank under the Eastern Block. The Eastern and Western Blocks were brought together at approximately 1.8 billion years ago.
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These ophiolite series are widespread in Iran. Some of the more important locations include Kermanshah–Neyriz–Oman Belt, Makran (south of Jazmurian), ultramafic–mafic rocks related to Flysch Zone in Khash–Nosrat Abad–Birjand Belt, ultramafic and mafic rocks north of Dorooneh fault, Torbat-e Jam–Torbat-e Heydarieh–Sabzevar–Fariman regions, and Central Iran–Nain–Baft–Shahr-e Babak, Khoy–Maku. Ultramafic and mafic rocks also occur in association with large gabbroic intrusions. This type probably resulted from differentiation in a large mafic magma chamber, comparable to those of the layered mafic intrusions.
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VMS deposits associated with sub-equal proportions of mafic volcanic and siliciclastic rocks; felsic rocks can be a minor component; and mafic (and ultramafic) intrusive rocks are common. In metamorphic terranes may be known as or pelitic-mafic associated VMS deposits. The Besshi deposits in Japan and Windy Craggy, BC represent classic districts of this group.
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Generally, ultramafic and mafic igneous rocks have relatively high, and granites low, PGE trace content. Geochemically anomalous traces occur predominantly in chromian spinels and sulfides. Mafic and ultramafic igneous rocks host practically all primary PGM ore of the world. Mafic layered intrusions, including the Bushveld Complex, outweigh by far all other geological settings of platinum deposits.
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The entire area is also underlain by layered mafic rocks, which are thought to be a part of Pecos Mafic Igneous Suite, and extends into the southern US. It has been dated to 1163 mya.
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Other than hot subduction, such geotherms may also be possible during the delamination of mafic crustal base. The delamination may be attributed to mantle downwelling or an increase in density of the mafic crustal base due to metamorphism or partial melt extraction. Those delaminated meta-mafic bodies then sink down, melt, and interact with surrounding mantle to generate TTGs. Such delamination induced TTG generation process is petrogenetically similar to that of subduction, both of which involves deep burial of mafic rocks into the mantle.
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The rocks have shoshonitic, mafic and calc-alkaline composition. The magma feeding these volcanic centres appears to come from the asthenosphere and the ascent of mafic magmas is facilitated by the extensional tectonic regime and by faulting.
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Its eruption was presumably linked to high mantle melt rates; the resulting mafic magmas induced the generation of large amounts of silicic melts. Lower mantle melt rates would form mafic melts that incorporate silicic melts before erupting.
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Of these volcanic vents, Olallie Butte and Sisi Butte are the two largest mafic (rich in magnesium and iron) shield volcanoes. Olallie Butte marks part of a region of basaltic andesite eruptions, also prominent at Three Fingered Jack, that extends north and south from Mount Jefferson. Olallie Butte is considered a shield volcano, though it has a conical shape that serves as a transitional morphology between steep, mafic volcanoes like Mount McLoughlin and Mount Thielsen and flatter, mafic shields. Made of basaltic andesite, it has a mafic composition.
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Extensive erosion and faulting has affected the southern part of the terrane since the Neogene. The Mesozoic rocks on the island are divided into the North Coast Schist, mafic plutonic rocks, the Tobago Volcanic Group and mafic dikes.
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The South Coast of Ascension has old, highly mafic lava flows. Bentmoreite flows are most common, although a basalt flow outcrops in Crystal Bay, a mafic scoria cone forms Ragged Hill and trachyte outcrops immediately south of the hill.
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The mountain consist of mostly non-alkaline mafic rock from the middle Pleistocene.
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The bottom layer of the pumice is white felsic rich pumice with a darker grey mafic pumice overlying it. These changes represent the increasing vigour of the eruption. The mafic upper part of the deposit reflects the increasing depth of the origin or compositionally zoned magma chamber (mafic lava is denser and settles to the bottom of the chamber as well as crystals which settle out, e.g., olivine).
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Lava composition varies, but usually it is low-viscosity, mafic to ultramafic in composition.
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Modelling indicates a system where andesitic melts coming from the mantle rise through the crust and generate a zone of mafic volcanism. Increases in the melt flux and thus heat and volatile input causes partial melting of the crust, forming a layer containing melts reaching down to the Moho that inhibits the ascent of mafic magmas because of its higher buoyancy. Instead, melts generated in this zone eventually reach the surface, generating felsic volcanism. Some mafic magmas escape sideward after stalling in the melt containing zone; these generate more mafic volcanic systems at the edge of the felsic volcanism, such as Cerro Bitiche.
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Crystal Bay, Minnesota Bytownite is a rock forming mineral occurring in mafic igneous rocks such as gabbros and anorthosites. It also occurs as phenocrysts in mafic volcanic rocks. It is rare in metamorphic rocks. It is typically associated with pyroxenes and olivine.
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The more mafic nature of the crust meant that higher amounts of water molecules (OH) could be stored the altered parts of the crust. At subduction zones this mafic crust was prone to metamorphose into greenschist instead of blueschist at ordinary blueschist facies.
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They are massive blocky outcrops made up of crystals of feldspar, quartz and mafic minerals.
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The Skaergaard intrusion is a layered mafic intrusion in eastern Greenland formed 55 million years ago during the opening of the North Atlantic Ocean. Skaergaard is one of the world's foremost examples of a layered mafic intrusion which exhibits exceptionally well-developed cumulate layering.
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Mafic rocks are distributed within the entire Acasta Gneiss Complex as minor blocks such as enclaves and bands. The mafic rocks consist of massive to slightly foliated amphibolite, garnet amphibolite as well as hornblendite. Mineral composition indicates that they had experienced metamorphism between amphibolite to upper amphibolite facies.
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The zone also includes smaller includes of quartz schist and chlorite schist and layered non-mylonite mafic rocks.
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The peak of Mount Tomuraushi consists of mainly non-alkalai mafic rock from the Pleistocene to the Holocene.
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Mount Maru consists of non-alkali, mafic, volcanic rock. The andesitic volcano is topped with a lava dome.
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The lavas are potassium- rich dacitic and rhyolitic save for an andesitic mafic component, and rich in crystals.
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Mount E consists of non-alkali, mafic, volcanic rock. The andesitic volcano is topped with a lava dome.
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Dominant rocks in the region are variably deformed tonalitic, granodioritic, and granitic, and amphibolitic gneisses. Mafic rocks such as amphibolite and ultra mafic rocks are also present in Acasta Gneiss Complex and occur in variable proportions throughout the Complex. A north-east trending fault divide the area into two domain.
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In the younger emplacements, clinopyroxene is evident along with an increase in mafic content.Hildreth et al. (1984), p. 50.
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Felsic magmatism dominates the north and south areas of Labrador while mafic magmatism dominates the central area of Labrador.
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Spinel is found as a metamorphic mineral, and also as a primary mineral in rare mafic igneous rocks; in these igneous rocks, the magmas are relatively deficient in alkalis relative to aluminium, and aluminium oxide may form as the mineral corundum or may combine with magnesia to form spinel. This is why spinel and ruby are often found together. The spinel petrogenesis in mafic magmatic rocks is strongly debated, but certainly results from mafic magma interaction with more evolved magma or rock (e.g. gabbro, troctolite).
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This includes basalt, hawaiite, mugearite, benmoreite, trachyte and rhyolite. Potassium-argon dating indicates that the oldest rocks exposed above the water are one million year old rhyolites. Geologists have divided the island's mafic and felsic rocks into different named sequences and sub-divided mafic rocks based on their ratio of zirconium and niobium.
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St. John's Island peridot information and history at Mindat.org Olivine occurs in both mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks. Mg-rich olivine crystallizes from magma that is rich in magnesium and low in silica. That magma crystallizes to mafic rocks such as gabbro and basalt.
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Dykes formed later with a mafic dyke injected first followed by a felsic material. A feldsparphyric dyke crosses the island east–west near the ferry pier. Several Cenozoic age quartzphyric rhyolite dykes cross the island. These are also injected with narrow dacitic dykes, and last of all very fine grained mafic basaltic dykes.
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PDFGlikson A. 2004. Bedout basement rise, offshore northwestern Australia: evidence of an unshocked mafic volcanic hyaloclastite volcanic breccia. Eos Trans.
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Other economically significant PGE deposits include mafic intrusions related to flood basalts, and ultramafic complexes of the Alaska, Urals type.
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Postglacial, mafic eruptions are more common in the Sisters Reach — which includes Belknap — than anywhere in the Cascade volcanic arc. A lava flow lies next to South Cinder Peak, the Nash Crater–Lost Lake cone cluster, Sand Mountain Volcanic Field, Inaccessible Cone chain, Blue Lake Crater, and a number of monogenetic scoria cones and chains. The McKenzie and Santiam Pass area saw more than a dozen distinct mafic eruptions between 4,500 and 1,100 years ago according to radiocarbon dating, which corresponded to a pulse of mafic eruptions in the late Holocene epoch. Other nearby mafic eruptive units occur at Sims Butte, Cayuse Crater, LeConte Crater, Mount Bachelor, the Egan Cone cluster, and the Katsuk-Talapus chain, which likely were all emplaced between 18,00 and 8,000 years ago.
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Most of the surrounding volcanoes consist of mafic (basaltic) lavas; only South and Middle Sister have an abundance of silicic rocks such as andesite, dacite, and rhyodacite. Mafic magma is less viscous; it produces lava flows and is less prone to explosive eruptions than silicic magma. The region was active in the Pleistocene, with eruptions between about 650,000 and about 250,000 years ago from an explosively active complex known as the Tumalo volcanic center. This area features andesitic and mafic cinder cones such as Lava Butte, as well as rhyolite domes.
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However, in south-central and southeast Sweden, the younger rock does not appear to derive from the Archean rocks. Northern Sweden has greenstone belts, made up of mafic volcanic rocks with intercalations of komatiite, quartzite, graphite schist and Lapponian marble. Uranium-lead dating in the lower part of the Kiruna greenstone belt indicates mafic volcanism started in the Archean around 2.7 billion years ago and ended before the intrusion of mafic dikes 2.2 billion years ago. Quartzite, feldspathic meta-sandstone, mica schist and Jatulian dolomite are the other dominant metasupracrustal rocks in the area.
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The geochronology of Archean events strongly relies on U-Pb dating and Lu-Hf dating. Since mafic rocks (contain low silica content, such as basalt) are lack of zircon, only the age of felsic rocks can be dated among the volcanic rocks in greenstone belts. As felsic volcanic rocks are episodically deposited in between mafic layers, the age range of a particular mafic layer can be constrained by the upper and lower felsic volcanic layers. So, the time of occurrence and the duration of volcanic episodes can be revealed.
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This quiescence was followed by a mafic capping stage between 2.2 and 0.8 million years ago, but renewed activity might have occurred in the last 340,000 years. Alkali olivine basalts of the mafic capping stage were derived from the fractionation of a clinopyroxene, olivine and oxide assemblage. However, the associated hawaiite lavas may have derived from an alkali olivine basalt parent by the fractionation of a clinopyroxene-dominated assemblage at higher pressures. As volcanic activity waned during the mafic capping stage, lava flows became more viscous and decreased in volume.
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The 758,000 year old intermediate bentmoreite lava flows of southwest Ascension are interspersed with scoria cones and periodically mafic ash falls.
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With an increase in calcic plagioclase and mafic minerals the rock type becomes a diorite. The volcanic equivalent is the latite.
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This is explained by gabbroic and granitic intrusion within the suture zone, with the low amount of unltra-mafic rocks involved.
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Granite has a felsic composition and is more common in continental crust than in oceanic crust. They are crystallized from felsic melts which are less dense than mafic rocks and thus tend to ascend toward the surface. In contrast, mafic rocks, either basalts or gabbros, once metamorphosed at eclogite facies, tend to sink into the mantle beneath the Moho.
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Mafic magmas are more liable to flow, and are therefore more likely to undergo periodic replenishment of a magma chamber. Because they are more fluid, crystal precipitation occurs much more rapidly, resulting in greater changes by fractional crystallisation. Higher temperatures also allow mafic magmas to assimilate wall rocks more readily and therefore contamination is more common and better developed.
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The sima has a higher density (2800 to 3300 kg/m3) than the sial, which is due to increased amounts of iron and magnesium, and decreased amounts of aluminium. When the denser sima comes to the surface it forms mafic rocks, or rocks with mafic minerals. The most dense sima has less silica and forms ultramafic rocks.
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The Granitic Seychelles form the northernmost part of the Mascarene Plateau. There are mafic xenolith intrusions in the granite in some areas.
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Ground-based astronomers in August 1998 briefly observed a high- temperature eruption at Masubi, confirming Masubi Fluctus' silicate mafic to ultramafic composition.
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Many pale ignimbrites are dacitic or rhyolitic. Darker-coloured ignimbrites may be densely welded volcanic glass or, less commonly, mafic in composition.
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Matachewan Dike Swarms Swarms of mafic dikes and sills are typical of continental rifting and can be used to time supercontinent breakup. Intrusion of the 2,475- to 2,445-million-year-old Matachewan-Hearst Mafic Dike Swarm and the 2,490- to 2,475-million-year-old East Bull Lake suite of layered mafic intrusive rocks are interpreted as indicating early Paleoproterozoic, mantle-hotspot driven rifting centered near Sudbury, Ontario, during the onset of Kenorland breakup. Radiometric dating shows that the Wyoming province's Blue Draw Metagabbro was undergoing rifting at , the same time the emplacement of the long belt of mafic layered intrusions in the Sudbury region. In the northern Black Hills of southwest South Dakota the 2,600- to 2,560-million-year-old Precambrian cystalline core, the Blue Draw Metagabbro, is a thick layered sill.
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Another characteristic of the late magmatism is the apparent lack of mafic and intermediate compositions among the magmas, which are nearly all felsic.
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The Kanichee layered intrusive complex, also called the Kanichee intrusion and Ajax intrusion, is a layered intrusion in Northeastern Ontario, Canada, located in the central portion of Strathy Township about northwest of the town of Temagami. It consists of mafic-ultramafic rocks and is the largest of many mafic-ultramafic intrusions associated with felsic and mafic metavolcanic rocks in the northern Archean Temagami Greenstone Belt. Five magmatic cycles have been identified in the Kanichee layered intrusive complex, the first of which formed a PGE deposit with associated gold, copper and nickel mineralization. Ore mineralogy includes pyrrhotite, pentlandite, chalcopyrite and pyrite.
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The Sister's Peak region in northwest Ascension has intermediate mafic lava flows, scoria cones and mafic ash fall deposits near Long Beach. The flows formed approximately 829,000 years ago and range between basalt, hawaiite and mugearite compositions. Benmoreite flows outcrop near Long Bay and west of Lady Hill. Additionally, benmoreite cinder cones are found near Broken Tooth and Hollow Tooth.
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The rhyolites of the Yellowstone Caldera are examples of volcanic equivalents of A-type granite. H-type granites were suggested for hybrid granites, which were hypothesized to form by mixing between mafic and felsic from different sources, e.g.M-type and S-type. However, the big difference in rheology between mafic and felsic magmas makes this process hardly happening in nature.
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Ideally, the stratigraphic sequence of an ultramafic-mafic intrusive complex consists of ultramafic peridotites and pyroxenites with associated chromitite layers toward the base with more mafic norites, gabbros and anorthosites in the upper layers. Some include diorite, and granophyre near the top of the bodies. Orebodies of platinum group elements, chromite, magnetite, and ilmenite are often associated with these rare intrusions.
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Modified from Moyen & Martin, 2012. Various evidence has shown that Archean TTG rocks were directly derived from preexisting mafic materials. The melting temperature of meta-mafic rocks (generally between 700 °C and 1000 °C) depends primarily on their water content but only a little on pressure. Different groups of TTG should therefore have experienced distinct geothermal gradients, which corresponding to different geodynamic settings.
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The mineralized zone consists of massive sulphides with a thin interbed of barren mafic tuff, not dissimilar from other parts of the Cayeli deposit.
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The concentration of Sm and Nd in silicate minerals increase with the order in which they crystallise from a magma according to Bowen's reaction series. Samarium is accommodated more easily into mafic minerals, so a mafic rock which crystallises mafic minerals will concentrate neodymium in the melt phase relative to samarium. Thus, as a melt undergoes fractional crystallization from a mafic to a more felsic composition, the abundance of Sm and Nd changes, as does the ratio between Sm and Nd. Thus, ultramafic rocks have high Sm and low Nd and therefore high Sm/Nd ratios. Felsic rocks have low concentrations of Sm and high Nd and therefore low Sm/Nd ratios (for example komatiite has 1.14 parts per million (ppm) Sm and 3.59 ppm Nd versus 4.65 ppm Sm and 21.6 ppm Nd in rhyolite).
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Geology of Rajasthan (Northwest India). Precambrian to Recent. Scientific Publishers (India), Jodhpur, 421 pp. The Raialo Group consists predominantly of mafic volcanic and calcareous rocks.
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The ignimbrite covered a total surface area of . This ignimbrite consists of rocks ranging from basaltic andesite to rhyolite with colours ranging from white to dark. Unusually for such mixed-composition ignimbrites, the rhyolites overlie the more mafic deposits. These mafic ignimbrites are not found around the entire lake, indicating that the magma chamber was asymmetric or its contents were erupted in an asymmetric fashion.
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Blocky 'a'a and ropy pāhoehoe flows characterized the fluid and effusive nature of volcanism at Level Mountain during the mafic shield- building stage. Lava flows of the mafic shield-building stage comprise four sub-horizontal units. Initial volcanism produced a thick sequence of columnar jointed alkali basalt flows and altered grey-green vesicular basalts which form the lowest unit. Subsequent activity deposited the overlying second thick unit.
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Their slopes are covered with their eruptive products and serve as the surface expressions of intrusions. As a result, they provide a unique opportunity to study the relationships between magma chambers and their lavas. The mafic (rich in magnesium and iron), intermediate (between mafic and felsic) and felsic (rich in feldspar and quartz) volcanic rocks of the massif were erupted from at least eight volcanic vents.
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The ultramafic-mafic rocks exhibit a band within the K-feldspar-rich granites.The K-feldspar-rich granites are found in the southwestern of the Huangling Complex.
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Tata Sabaya has produced "two-pyroxene" andesite and porphyritic andesite. Minerals contained within the rock are augite, biotite, hornblende, hypersthene, plagioclase and titanomagnetite with only little variation between rocks erupted during separate stages of volcanic activity. The erupted volcanites define a potassium-rich calc-alkaline suite. Inclusions of more mafic rocks in the erupted material may indicate that mafic magma was injected into the magma chamber of Tata Sabaya.
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Crustal recycling derived the TTG surrounding the Nuvvuagituq Belt from arc-like source rocks, i.e. Ujaraaluk Unit. A large scale of a simultaneous accumulation of TTG and subsequent partial melting only occurs in particular tectonic settings. It is viable that the production is related to crust recycling in which the mafic crust and water were returned to the mantle, and as a consequence, arc-like mafic magma formed.
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In 1992 researchers first used the term large igneous province to describe very large accumulations—areas greater than 100,000 square kilometers (approximately the area of Iceland)—of mafic igneous rocks that were erupted or emplaced at depth within an extremely short geological time interval: a few million years or less. Mafic, basalt sea floors and other geological products of 'normal' plate tectonics were not included in the definition.
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Spectra of the dark areas are consistent with the presence of ferrous iron (Fe2+) in mafic minerals and show absorption bands suggestive of pyroxene, a group of minerals that is very common in basalt. Spectra of the redder dark areas are consistent with mafic materials covered with thin alteration coatings.Barlow, N.G. (2008). Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK, pp. 81-82.
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More rare rock associations include mafic and ultramafic layered intrusions and one of the world's oldest ophiolites. The region hosts valuable deposits of gold, chromium, iron and phosphate.
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Mafic intrusions of gabbro of the Duluth Complex anchor both ends of the highlands, to the west of Duluth and above Grand Portage Bay to the east. Between them is an area of basaltic rocks of the North Shore Volcanics, interspersed with occasional mafic rocks. These basaltic layers, formed from lava emitted from rift fissures in the center of what is now Lake Superior, subsided in the middle (forming the present lake basin); the edges angle upward from the lake in a serrated series of ridges known as the Sawtooth Mountains along the lakeshore. Both the mafic and volcanic rocks have been partially eroded, leaving the more resistant rock standing above the surrounded country.
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Mixed compression and extension caused broad mafic magmatism during this time. This could be related to the Shawinigan orogeny which occurred in the southwestern region of the Grenville Province.
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It is difficult to precisely determine what causes large ultramafic – mafic intrusives to be emplaced within the crust, but there are two main hypotheses: plume magmatism and rift upwelling.
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Grayson Glades Natural Area Preserve is a Natural Area Preserve located in Grayson County, Virginia. Its centerpiece is an extremely rare wetland type known as a "mafic fen", which are situated upon soils rich in magnesium and fed by springs. The site is at the headwaters of a small stream system supporting additional mafic fens. Among the rare species found on the property are tuberous grass-pink (Calopogon tuberosus), ten-angled pipewort (Eriocaulon decangulare var.
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It underlies a large portion of northwestern Strathy Township and is penetrated by mafic intrusions, although the Kanichee Intrusion consists of peridotite and pyroxenite, which are ultramafic rocks. Just to the southeast, the Younger Volcanic Complex consists mainly of mafic volcanic rocks that form four geologic formations. The Arsenic Lake Formation is composed of dark green, iron-rich, massive and pillowed tholeiitic basalts. Throughout the Arsenic Lake Formation are feldspar-phyric basaltic lava flows.
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However, the natural carbonation rates of these rocks are too slow to significantly offset anthropogenic CO2 emissions. Therefore, scientists are currently investigating if it is possible to geoengineer CO2 uptake in mafic and ultramafic rocks so that this CO2 uptake happens more quickly. This could be done, perhaps, by fracturing and heating and injection of CO2-rich fluids. This is already being tested in mafic basalts through the CarbFix Project in Iceland.
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The geological formations recorded in the river basin consist generally of a metapelitic sequence. Mafic intrusives have been noted in the locally metamorphosed zones. The Bluestone basin features mica and chlorite schists, beds of limestone, intrusive mafic masses altered to greenstone, and small quartz veins, particularly in the Gold Run Creek, a southern and eastern tributary of the Bluestone River. In some areas, minerals recorded are blueschist facies and retrograde greenschist facies.
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It has a width of and a depth of . Predominantly, it has generated mafic (rich in magnesium and iron) lava, producing about of magma within the past 15,000 years. Moreover, many of the identified eruptive vents from the Quaternary include scoria cones or other mafic vents. The High Cascades graben displays a unique geochemical signature with low-K tholeiite magma and a relatively enriched mantle source, produced by extension and heat flux.
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Stratiform deposits are formed as large sheet-like bodies, usually formed in layered mafic to ultramafic igneous complexes. This type of deposit is used to obtain 98% of the worldwide chromite reserves. Stratiform deposits are typically seen to be of Precambrian in age and are found in cratons. The mafic to ultramafic igneous provinces that these deposits are formed in were likely intruded into continental crust, which may have contained granites or gneisses.
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Magma mixing occurs when magmas of a different composition intrude a larger magma body. In some cases, the melts are immiscible and stay separated to form pillow like collections of denser mafic magmas on the bottom of less dense dense felsic magma chambers. The mafic pillow basalts will demonstrate a felsic matrix, suggesting magma mingling. Alternatively, the melts mix together and form a magma of a composition intermediate to the intrusive and intruded melt.
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The geology of the U.S. Virgin Islands includes mafic volcanic rocks, with complex mineralogy that first began to erupt in the Mesozoic overlain and interspersed with carbonate and conglomerate units.
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The highlands of the peninsula contain amphibolite and eclogite mafic rocks which, like tholeiitic metabasalt, are similar to the rocks found both on island arcs and on mid-ocean ridges.
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Usually, only mafic flows will erupt as pāhoehoe, since they often erupt at higher temperatures or have the proper chemical make-up to allow them to flow with greater fluidity.
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Pegmatite with large quartz, huge perthitic alkali feldspar and mafic reaction seam Pegmatites do occur as well, mainly as dikes; in some places as amygdules with beautiful smoky quartz (rare).
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Mount Rishiri is made up of alkali and non- alkali mafic volcanic rock dating from the Late Pleistocene, 130,000–18,000 years ago. Otherwise it is covered in Quaternary volcanic rock debris.
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It is worth reiterating that magma chambers are not usually static single entities. The typical magma chamber is formed from a series of injections of melt and magma, and most are also subject to some form of partial melt extraction. Granite magmas are generally much more viscous than mafic magmas and are usually more homogeneous in composition. This is generally considered to be caused by the viscosity of the magma, which is orders of magnitude higher than mafic magmas.
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The granite and pegmatite of Attappad9 represent the post-kinematic intrusives. Many dolerite dykes also have been reported from this area. The bands and layers of ultramafics and mafic rocks (Ultramafic and mafic rocks represented by metapyroxinite, talc-tremolite-actinolite schist and amphibolites) of varying dimension, BIF, sillimamite/kyanite bearing quartzite and fuchsite quartzite occurring within the Peninsular Gneissic Complex of Attappady area designated as Attappady Supracrustals. Remnants and enclaves of Attappady supracrustals occur within the gneisses.
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Rodingite from Maryland Rodingite is a metasomatic rock composed of grossular- andradite garnet and calcic pyroxene; vesuvianite, epidote and scapolite. Rodingites are common where mafic rocks are in proximity to serpentinized ultramafic rocks. The mafic rocks are altered by high pH, Ca2+ and OH- fluids, which are a byproduct of the serpentinization process, and become rodingites. The mineral content of rodingites is highly variable, their high calcium, low silicon and environment of formation being their defining characteristic.
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Archean TTG rock outcrop in Kongling Complex, South China Craton. The white TTG rock body is intruded by dark mafic dikes, as well as light color felsic dikes. The mafic minerals in the TTG rock body, possibly biotite, were weathered, which introduced a brownish coating on the TTG rock surface. Tonalite-trondhjemite-granodiorite rocks or TTG rocks are intrusive rocks with typical granitic composition (quartz and feldspar) but containing only a small portion of potassium feldspar.
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The Alwar Group mainly consists of arenaceous and mafic volcanic rocks. The Ajabgarh Group is dominated by carbonate, mafic volcanic and argillaceous rocks. In the southern part, similar rock types, despite different names, are identified, where they are Gogunda Group (equivalent to Alwar group) and the Kumbhalgarh Group (equivalent to Ajabgarh Group).Gupta, S.N.; Arora, Y.K.; Mathur, R.K.; Iqbaluddin, Prasad B.; Sahai, T.N.; Sharma, S.B.. The Precambrian geology of the Aravalli region, southern Rajasthan and northeastern Gujarat.
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Hawaiite was the most extensively erupted lava of the mafic capping stage, occurring mostly at the southern end of the Itcha Range but also in its interior. Volcanism of the mafic capping stage began with the eruption of aphyric hawaiite lava flows. These were extruded from dikes and dissected cinder cones in the central and southeastern parts of the Itcha Range. Alkali olivine basalts were erupted contemporaneously from younger better preserved cinder cones and form lava flows reaching thick.
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The Windimurra Igneous Complex is a giant ultramafic-mafic intrusion emplaced within the Yilgarn craton of Western Australia. It is located approximately 100 kilometres south east of the town of Mount Magnet.
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Until that point, differentiation and crystallization of rising mafic magmas had mostly produced andesitic magmas. The change in plate movements and increased melt generation caused an overturn and anatexis of the melt generating zone, forming a density barrier for mafic melts which subsequently ponded below the melt generating zone. Dacitic melts escaped from this zone, forming diapirs and the magma chambers that generated APVC ignimbrite volcanism. Magma generation in the APVC is periodical, with pulses recognized 10, 8, 6, and 4 mya.
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Layers of mafic and ultramafic intrusive rocks forming the mountain of Hallival The Rum layered intrusion is located in Scotland, on the island of Rùm (Inner Hebrides). It is a mass of intrusive rock, of mafic-ultramafic composition, the remains of the eroded, solidified magma chamber of an extinct volcano that was active during the Palaeogene Period. It is associated with the nearby Skye intrusion and Skye, Mull and Egg lavas. It was emplaced 60 million years ago above the Iceland hotspot.
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Listwanites are important rocks to study for a number of reasons. First of all, listwanites contain large amounts of CO2 which originated from fluids that is now stored in solid mineral form. Recently, geologists and other scientists have been investigating the potential of storing CO2 in solid minerals (which are more stable than CO2 stored as a liquid or gas) through carbonation of mafic and ultramafic rocks (ref1). Mafic and ultramafic rocks take up significant CO2 through their natural alteration processes.
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Also, if an eruption column were to be produced, it would disrupt local air traffic. Volcanic ash reduces visibility and can cause jet engine failure, as well as damage to other aircraft systems. Renewed volcanism is likely to result in the creation of mafic cinder cones, with the latest such event having occurred with the eruption of Nazko Cone 7,200 years ago. However, eruptions of less mafic magma, typical of earlier activity of the Anahim hotspot, cannot be ruled out.
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The Bravo Lake Formation is a mafic volcanic belt and large igneous provinceIgneous rock associations in Canada 3. Large Igneous Provinces (LIPs) in Canada and adjacent regions: 3 Retrieved on 2007-01-10 located at the northern margin of the Trans-Hudson orogeny on central Baffin Island, Nunavut, Canada. It is exposed along a nearly continuous east-west passage for and changes in stratigraphic thickness from 1 to 2.5 kilometers.Central Baffin Island 4-D Project - Projects : Paleoproterozoic mafic magmatism in central Baffin Island.
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The magmatic evolution of the flood basalts show evidence of different parental magmas, fractionation, and open system processes. Mafic tholeittic samples model N-MORB magmas from a depleted mantle source and likely experienced a small amount of crustal contamination in the form of light rare earth element enriched, crust-derived melt. The presence of MORB-like rocks could indicate that an asthenospheric mantle source was important in west-central Madagascar. Some mafic rocks of transitional-alkaline composition fractionated to evolved basaltic composition.
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The caldera is also a coalescence of at least two large mafic shield volcanoes that formed more than 2703 million years ago.Blake River Group evolution: characteristics of the subaqueous Misema and New Senator calderas The rim of the Misema Caldera contains a 10-15 kilometre wide inner and outer ring zone, in which many mafic ring dike complexes and subaqueous pyroclastic sediments are detected. The mafic ring dike structures may be deeper level expressions of summit calderas related to a shield volcano phase while the pyroclastic fragments could either be associated with satellite cones or the result of Misema caldera collapse. The Misema Caldera is the oldest and largest caldera associated with the Blake River Megacaldera Complex and is comparable in size to the Lake Toba caldera in Indonesia.
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There are three explosion craters at the summit. At at about , there is a fumarole. The volcano is made mostly from non-alkalai mafic volcanic rock. The main rock type is andesite and dacite.
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Browns Field is situated on a maar- diatreme. It was around 200 metres in diameter. The mafic soils are a typical dark colour. The diatreme occurred in the early Jurassic, around 200 million years ago.
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Geological Society of America Bulletin, v. 74, p.407-436. Mafic intrusive rocks are present locally in the lower portion. Much of the sedimentation probably occurred between about 1450 and 1400 Ma (million years) ago.
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When felsic melts reach the surface of the Earth, they are generally very explosive (i.e. Mount St. Helens). Mafic melts generally flow over the surface of the Earth and form layers (i.e. Columbia River Basalt).
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The chemistry of Lascar's rocks is fairly similar to those of neighbouring Tumisa volcano. Magma erupted by Lascar appears to form from the mixing of mafic and more evolved magmas; the 1993 eruption deposits contain bands of different rocks. Specifically, basaltic andesite magma is periodically injected into a magma chamber, where crystal fractionation and mixing processes take place. The process happens frequently, thus the magmas are relatively unevolved; presumably, if the supply of mafic magma is steady, the products are andesitic, otherwise dacite forms.
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Geologists debate the exact origins of the island and some have proposed that Ascension Island may overlie a diverted shallow mantle plume. Alternately, the island may have originated from anomalously enriched magma, originally at the Mid-Atlantic Ridge, but now situated to the west of it. The petrology of Ascension is unusual. Compared to most other volcanic islands, which only have a few mafic and felsic endmembers such as basalt or rhyolite, Ascension has a full-range from some of the most mafic to most felsic.
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The postglacial activity appears to originate from a shallow silicic magma chamber beneath the caldera. Research published in 2017 indicates that this system is somewhat heterogeneous with distinct compositions of magmas erupted in the northwesterly and southeasterly parts of the volcanic field. The early post-glacial rhyodacites contain mafic inclusions implying that mafic lavas exist but do not reach the surface. From isotope ratios it has been inferred that the magma is of deep origin, and the rare-earth element composition shows no evidence of crustal contamination.
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Surface of a weathered pillow lava formation west of the Ontario Northland Railway. This is one of the several pillow lava outcrops throughout the Temagami Greenstone Belt The TGB consists of two large volcanic sequences that were formed during several phases of volcanic activity. These two sequences, known as the Older and Younger volcanic complexes, consist of volcanic rocks ranging in composition from felsic to mafic. The Older Volcanic Complex is composed mainly of felsic lava flows and pyroclastic deposits with smaller amounts of mafic volcanic rocks.
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Carbon dioxide has less severe impacts on mafic, felsic and rocks of other composition, such as carbonate rocks, chemical sediments, etcetera. The exception to this rule is the calc-silicate family of metamorphic rocks, which are also subjected to wide variations in mineral speciation due to the mobility of carbonate during metamorphism. Felsic and mafic rocks tend to be less affected by carbon dioxide due to their higher aluminium content. Ultramafic rocks lack aluminium, which allows carbonate to react with magnesium silicates to form talc.
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It consists of pyroclastic deposits, thin lava flows, flood basalts and central volcanoes, as well as hypabyssal sills and dikes. Argon–argon dating of mafic igneous rocks from the province suggests that mafic magmatism peaked during two time intervals. The first time interval between 127 and 129 million years ago was characterized by the widespread intrusion of sills and dikes. Flood basalt volcanism during the second time interval between 92 and 98 million years ago was coeval with the development of the proto-Arctic Ocean.
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Andesite and dacite lava flows from the volcano usually have plagioclase as their major phenocryst, though augite and hypersthene are also present, the latter more abundant. Olivine form minor phenocrysts, which are found throughout lava flows from Mazama, and hornblende can be found in some andesite lava flows. Basalt and mafic andesite lava flows from Mazama and nearby eruptive vents have relatively higher amounts of olivine and lack hypersthene, and the mafic andesite deposits display textures that indicate they underwent greater mixing than andesite and dacite deposits.
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In addition, NASA reported the rover found two principal soil types: a fine-grained mafic type and a locally derived, coarse- grained felsic type. The mafic type, similar to other martian soils and martian dust, was associated with hydration of the amorphous phases of the soil. Also, perchlorates, the presence of which may make detection of life- related organic molecules difficult, were found at the Curiosity rover landing site (and earlier at the more polar site of the Phoenix lander) suggesting a "global distribution of these salts".
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Augite is an essential mineral in mafic igneous rocks; for example, gabbro and basalt and common in ultramafic rocks. It also occurs in relatively high-temperature metamorphic rocks such as mafic granulite and metamorphosed iron formations. It commonly occurs in association with orthoclase, sanidine, labradorite, olivine, leucite, amphiboles and other pyroxenes. Occasional specimens have a shiny appearance that give rise to the mineral's name, which is from the Greek augites, meaning "brightness", although ordinary specimens have a dull (dark green, brown or black) luster.
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The New Senator Caldera is a large Archean caldera complex within the heart of the Blake River Megacaldera Complex, Quebec, Canada. It has a diameter of 15-30 kilometers and is made of thick massive mafic sequences. The caldera complex has inferred to be a subaqueous lava lake during the early stages of the caldera's development.ASH FALL: Newsletter of the Volcanology and Igneous Petrology Division Geological Association of Canada Retrieved on 2007-09-21 Gabbro sills represent lava lakes, which are common in mafic summit calderas.
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Unlike the arc-continent collision model, the rift closure model suggests there was a coherent Archean Eastern Block. It was separated into the Longgang and the Langrim blocks in early Paleoproterozoic with an ocean in between. As the block started to separate, mafic and granitic melts intruded the crust 2.2–2 billion years ago and sedimentary and volcanic rock sequences were formed 2–1.95 billion years ago. For example, A-type granites, mafic and felsic igneous parent rocks of greenschist and lower amphibolite facies were formed.
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Diabase Diabase () or dolerite or microgabbro is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). Diabase is the preferred name in North America, while dolerite is the preferred name in the rest of English-speaking world, where sometimes the name diabase is applied to altered dolerites and basalts. Some geologists prefer the name microgabbro to avoid this confusion.
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The lavas erupted in 1669 define a sodic hawaiite suite with two distinct acidic and mafic members that were erupted before and after 20 March, respectively. These two magmas formed through fractional crystallization processes in different parts of Mount Etna's plumbing system. It appears that prior to the 1669 eruption, a batch of more acidic magma was residing underneath Etna. A batch of new, more mafic magma that was more buoyant than the residing magma penetrated and traversed the magmatic system, and reached the surface.
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Mafic or basaltic lavas are typified by their high ferromagnesian content, and generally erupt at temperatures in excess of . Basaltic magma is high in iron and magnesium, and has relatively lower aluminium and silica, which taken together reduces the degree of polymerization within the melt. Owing to the higher temperatures, viscosities can be relatively low, although still thousands of times higher than water. The low degree of polymerization and high temperature favors chemical diffusion, so it is common to see large, well-formed phenocrysts within mafic lavas.
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The main source of rock in this formation is basalt, but both mafic and felsic rocks are present, so this formation is officially called a Flood Basalt Province. The inclusion of mafic and felsic rock indicates multiple other eruptions that occurred and coincided with the one-million-year-long eruption that created the majority of the basaltic layers. The traps are divided into sections based on their chemical, stratigraphical, and petrographical composition. One of the World Heritage Sites, the Putorana Plateau, is composed of Siberian Traps.
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VMS deposits associated with geological environments dominated by mafic rocks, commonly ophiolite sequences. The Cyprus and Oman ophiolites host examples and ophiolite-hosted deposits are found in the Newfoundland Appalachians represent classic districts of this subclass.
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North Sister (of the Three Sisters volcano complex) and Mount Washington mark isolated volcanic centers among the highly mafic (rich in magnesium and iron) platform of the central High Cascade arc. About 4.5 million years ago, eruption of mafic lava filled a subsiding Pliocene depression, creating the modern, mafic High Cascades. Compared to the eruptive products at and near North Sister, lava deposits at Mount Washington have a greater abundance of incompatible elements (elements unsuitable in size and/or charge to the cation sites of the minerals of which it is included.) The nearby lava dome and tuya (subglacial volcano) Hogg Rock shows more similarity to the basaltic andesite deposits at North Sister, which are poorly enriched in incompatible elements. The part of the High Cascades that extends south from Mount Jefferson to Santiam Pass includes shield volcanoes, lava domes, and cinder cones.
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Tonalities were formed in Neoproterozoic, by partial melting of Yangtze Craton during subduction beneath the North China Craton. As the oceanic Yangtze Craton subducted under the continental North China Craton, magmatic activities result in the formation of hydrated mafic basaltic magma. On the other hand, trondhjemites were formed in Archean, with the source from partial melting of Archean amphibolites and granulites under the continental Yangtze Craton in a high-pressure condition. They are composed of felsic minerals such as plagioclase, quartz, and Na-K-rich feldspar and minor mafic minerals biotite and hornblende.
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The mafic shield- building stage began with the eruption of thin mafic lava flows over an erosion surface. Successive eruptions sent lava pouring in all directions from central vents, forming a broad, gently sloping volcano of flat, domical shape, with a profile much like that of a warrior's shield. Alkali basalts and ankaramites were the primary lavas produced during this stage of activity which, due to their low silica content, were able to travel great distances away from their source. These lavas also erupted from vents on the flanks of the volcano.
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Assimilation is a popular mechanism for explaining the felsification of ultramafic and mafic magmas as they rise through the crust. Assimilation assumes that a hot primitive melt intruding into a cooler, felsic crust will melt the crust and mix with the resulting melt. This then alters the composition of the primitive magma. Also pre-existing mafic host rocks can be assimilated, with little effect on the bulk magma chemistry J. Leuthold, J. C. Lissenberg, B. O'Driscoll, O. Karakas; T. Falloon, D.N. Klimentyeva, P. Ulmer (2018); Partial melting of the lower oceanic crust at spreading ridges.
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Red arcuate line indicates boundary between vertical flow and horizontal flow. The Mackenzie dike swarm is the largest dike swarm known on Earth and is one of the several dike swarms found throughout the Canadian Shield. Mafic dikes cut Archean and Proterozoic rocks of the Canadian Shield, including those in the Athabasca Basin in Saskatchewan, the Thelon Basin in Nunavut and the Baker Lake Basin in the Northwest Territories. The mafic dikes display evidence that the unmetamorphosed basin-fill sequence was deposited before the Mackenzie dikes were intruded into the associated basins.
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The eruption was one of several postglacial mafic events in the area, which are more common in the Sisters Reach than anywhere in the Cascade arc. It was part of a pulse of more than a dozen mafic eruptions during the late Holocene epoch in the McKenzie and Santiam Passes region between 4,500 and 1,100 years ago. Isopach mapping of the deposits from Blue Lake Crater suggest an eruptive volume of . The eruption was predominantly fed by magma and produced thick scoria fall, which overlies phreatomagmatic surge deposits with thicknesses up to .
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The majority of rock in the region consists of normally polarized material less than 730,000 years old. Hoodoo Butte is part of the Sisters Reach, which extends from South Cinder Peak to Crane Prairie Reservoir, running for . With at least 466 volcanoes active during the Quaternary, it has a high vent density, with many mafic (rich in magnesium and iron) volcanoes of Pleistocene to Holocene age. Hoodoo Butte is one of the larger mafic volcanoes, along with Three Fingered Jack, North Sister, and the vents of the Mount Bachelor chain.
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By , Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. As the molten outer layer of Earth cooled it formed the first solid crust, which is thought to have been mafic in composition. The first continental crust, which was more felsic in composition, formed by the partial melting of this mafic crust. The presence of grains of the mineral zircon of Hadean age in Eoarchean sedimentary rocks suggest that at least some felsic crust existed as early as , only after Earth's formation.
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Lithologies vary from largely ultramafic peridotite, chromitite, harzburgite, and bronzitite in the lower sections to mafic norite, anorthosite, and gabbro toward the top, and the mafic Rustenburg Layered Suite is followed by a felsic phase (the Lebowa Granite Suite). The orebodies within the complex include the UG2 (Upper Group 2) reef containing up to 43.5% chromite, and the platinum-bearing horizons Merensky Reef and Platreef. The Merensky Reef varies from 30 to 90 cm in thickness. It is a norite with extensive chromitite and sulfide layers or zones containing the ore.
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Dacitic magma at the Lassen center formed from mafic (rich in magnesium and iron) magma meeting silicic (high in silicon dioxide) magma chambers with felsic (rich in feldspar and quartz) phenocrysts. Some dacitic crystals were partially reabsorbed as a result of mixing of hot mafic magma with cool dacitic magma, and this along with undercooling of mixed magma led to phenocryst variation within certain domes exceeding variation between the domes. All three sequences — Bumpass, Eagle Peak, and Twin Lakes — formed from lava subjected to magma-mixing processes, accounting for their heterogeneous appearance and composition.
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However, terrestrial contamination, as the source of the organic compounds, could not be ruled out. On September 26, 2013, NASA scientists reported that Curiosity detected "abundant, easily accessible" water (1.5 to 3 weight percent) in soil samples at the Rocknest region of Aeolis Palus in Gale. In addition, the rover found two principal soil types: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic type, similar to other martian soils and martian dust, was associated with hydration of the amorphous phases of the soil.
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The most northeastern tip of the Kasubuya license encompasses some Upper Nyanzian Formation comprising well-exposed banded iron formation and felsic tuffs and poorly-exposed pillowed tholeiitic basalt lava and mafic tuffs typical of the Geita greenstone belt.
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Eight to ten sequences of columnar jointed alkali basalt comprise this unit and have a total thickness of . All four sub- horizontal units of the mafic shield-building stage were deposited over a timespan of six million years.
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Mars Exploration Rover Mission: Press Release Images: Opportunity Minerals typical weathering products of mafic igneous rocks were found.Baird, A. et al. 1976. Mineralogic and Petrologic Implications of Viking Geochemical Results From Mars: Interim Report. Science: 194. 1288–1293.
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Mechanism Bimodal volcanism is the eruption of both mafic and felsic lavas from a single volcanic centre with little or no lavas of intermediate composition. This type of volcanism is normally associated with areas of extensional tectonics, particularly rifts.
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Retrieved 2015-07-20. Litchfieldite is composed of two varieties of feldspar (mostly albite but also some microcline), with nepheline, sodalite, cancrinite and calcite. The mafic minerals, when present, are magnetite and an iron-rich variety of biotite (lepidomelane).
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Hogg Rock, Three Fingered Jack, Mount Jefferson, and U.S. 20 near Santiam Pass North Sister and Mount Washington mark isolated volcanic centers among the highly mafic (rich in magnesium and iron) platform of the central High Cascades. About 4.5 million years ago, eruption of mafic lava filled a subsiding Pliocene depression, creating the modern mafic edifice of the High Cascades. Compared to the eruptive products at and near North Sister, lava deposits at Mount Washington have a greater abundance of incompatible elements (elements unsuitable in size and/or charge to the cation sites of the minerals of which it is included.) Hogg Rock shows more similarity to the basaltic andesite deposits at North Sister, which are poorly enriched in incompatible elements. The part of the High Cascades that extends south from Mount Jefferson to Santiam Pass includes shield volcanoes, lava domes, and cinder cones.
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The geological history of the Labrador Trough spans several tens of millions of years ranging from around 2.2 Ga to 1.74 Ga: # Following rifting along the Archean margin of the Superior craton about 2.2 billion years ago, rocks of the western part of the Labrador Trough were deposited. This period corresponds to the onset of first- cycle sedimentation and is characterized by the deposition of immature sediments, slightly alkaline volcanics, and the intrusion of mafic dykes. # Deposition of passive margin sediments, MORB-like mafic volcanism and intrusion of mafic sills characterize most of the first cycle between approximately 2.17 and 2.14 Ga. The end of the cycle (<2.06 Ga) is marked by the deposition of dolomite and chert on a restored platform. # Second-cycle platform and basin sedimentation occurred from 1.88 to 1.87 Ga and is associated with a new rifting episode or development of a fore-trough basin.
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Réunion is a mafic island formed as a result of the Réunion hotspot in the Indian Ocean, the same hotspot that produced the massive basalt flows of the Deccan Traps, when it was beneath India more than 66 million years ago.
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The rocks inside the vent were also changed by the contact, producing a sequence of alkali mafic igneous rocks as the magma assimilated the chalk, reducing the silica in the magma and leading to larger grain size near the contact.
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Dust is generally chondritic in composition. Its monomers contain mafic silicates, such as olivine and pyroxene. Silicates are rich in high-condensation temperature forsterite and enstatite. As these condense quickly, they tend to form very small particles, not merging droplets.
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The Crimson Creek Formation consists of greywacke with tholeiitic basalt. It is from 4000 to 5000 metres thick. This formation could be as late as the early Cambrian. The basalt is probably the same as mafic lavas of the Kanunnah Subgroup.
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The Windermere consists primarily of coarse-grained feldspathic conglomerates and pebbly sandstones, with lesser amounts of pelitic shales, dolomites, and limestones. Mafic igneous rocks are present in some areas. In most areas the Windermere rocks are highly sheared, faulted, and metamorphosed.
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Petrology indicates that the andesitic lavas of the southern domes are derived from the more silicic magmas by addition of more mafic andeistes. Conversely, the northern dome magmas formed by fractional crystallization with the most evolved components being erupted explosively.
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The source of ilmenite, garnet, sapphire and diamond is ultramafic and mafic rocks, such as kimberlite or basalt. Garnet is also sourced commonly from metamorphic rocks, such as amphibolite schists. Precious metals are sourced from ore deposits hosted within metamorphic rocks.
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VMS deposits associated with environments dominated by mafic volcanic rocks, but with up to 25% felsic volcanic rocks, the latter often hosting the deposits. The Noranda, Flin Flon-Snow Lake and Kidd Creek camps would be classic districts of this group.
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Layer sulfate unit in Northeast Syrtis. Megabreccia occurs throughout the basement unit of Northeast Syrtis. The composition of these megabreccias is complex, including altered or mafic material. These megabreccias may be uplifted and exposed by the Isidis Basin forming event.
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The Kam Group is a thick Archean volcanic group in the Yellowknife greenstone belt of the Northwest Territories, Canada. It consists of tholeiitic mafic and subordinate felsic volcanic rocks that were erupted in a submarine environment about 2706 million years ago.
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Most of this volcanism occurred in the southern segment, but the northern segment has also experienced mafic volcanism mostly associated with major volcanic centres and smaller volcanic fields such as Cerro Morado and Cerro Bitiche. Mafic lava flows however tend to constitute the minority of volcanic rocks in this region; the bulk of the volcanic rocks are dacitic-rhyolitic in composition. Present day volcanism occurs in the volcanic arc called the Central Volcanic Zone approximately farther west. The basement in the Cerro Morado area is formed by Ordovician rock formations and older lava flows of the Pairique volcanic complex and the Patahuasi flows.
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The Kanichee layered intrusive complex, also known as the Kanichee Intrusion and Ajax Intrusion, is the most voluminous mafic-ultramafic body in metamorphosed felsic and mafic volcanic rocks of the northern TGB. It is an oval-shaped layered intrusion that was formed during five phases of magmatic activity. A series of south-southeast dipping cyclic magmatic layers make up the intrusion, similar to those of the surrounding metamorphosed volcanic rocks, indicating that the rocks of the intrusion were formed horizontally and likely close to the surface. Numerous magmatic events may have breached the surface to produce volcanic eruptions.
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Granite, in Smögen (southwestern Sweden), formed during the Sveconorwegian orogeny The Paleoproterozoic rocks emplaced by the Svecokarelian orogeny were intruded by granite and mafic dikes, overlain with clastic sedimentary rocks and in some places, basalt. The granites range between 1.58 and 1.4 million years ago and some are rapakivi granite associated with syenite, gabbro and anorthosite. Swarms of mafic dikes are dated to 1.56-1.5, 1.25-1.2 and one billion to 900 million years ago, striking north-northwest in the western part of the Svecokarelian orogen. The Sveconorwegian Orogeny is 500 kilometers long and 180 kilometers wide.
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This is because the crust is usually less dense than the underplating magma, and this is the point at which the ascending magma reaches a level of neutral buoyancy. The evolving melt will remain here until it fractionates enough (through melting-assimilation-storage-homogenization (MASH) processes) that the remaining melt is less dense than the surrounding rock; the melt will then continue up into the crust, leaving behind the heavier mafic minerals which were crystallized during fractional crystallization. The assemblage of minerals remaining behind are typically mafic or ultramafic, and are responsible for the observed seismic anomaly which indicates underplated material.
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The terrane hosts a swarm of NEE-SSW oriented dykes that date to the Neoproterozoic. East of the SYSZ, the latitudinal Colonia Shear Zone (CSZ) separates the Palaeoproterozoic (2000±100 Ma) Piedra Alta Terrane to the north from the Tandilia Terrane to the south. A period of extensional tectonics in the Late Paleoproterozoic coincided with the formation and intrusion of the Piedra Alta mafic dike swarm and the rapakivi granites of Illescas Batholith. The 1790±5 Ma-old Late Palaeoproterozoic Piedra Alta mafic dike swarm was subsequently affected by the -wide Mesoproterozoic SYSZ and its eastern end bends along the dextral megashear zone.
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The Minerva Hills National Park sits on the Oligocene Minerva Hills Volcanics. These volcanics have been broadly divided into a basal series of mafic lavas (some 70 m thick) overlain by a series of intercalated mafic volcanics, felsic volcanics ranging from trachyte to rhyolite and trachytic pyroclastics. The pyroclastics are related to plugs and domes. The lower sequence has been dated at approximately 33 -34 Ma (million years) and the upper sequence 28.5–27.5 Ma. View of Minerva Hills National Park The Minerva Hills Volcanics is a remnant of Oligocene hot spot volcanism known as the Cosgrove Hot Spot.
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This has produced a long-lived volcanic field, with the earliest eruptions beginning at least 13 million years agoHeiken et al. 1990 and continuing almost to the present dayZimmerer et al. 2016 Both upper members of the tuff show compositional zoning, in which the lower pyroclastic flows are more silicic and contain less mafic (magnesium- and iron-rich) minerals than the upper flows. This is interpreted as progressive eruption of a gravitationally zoned magma chamber in which volatiles are concentrated at the top of the chamber and mafic minerals have partially settled into the lower, hotter portions of the magma chamber.
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It is however impossible to quantify the mineralogy of pegmatite in simple terms because of their varied mineralogy and difficulty in estimating the modal abundance of mineral species which are of only a trace amount. This is because of the difficulty in counting and sampling mineral grains in a rock which may have crystals from centimeters to meters across. Garnet, commonly almandine or spessartine, is a common mineral within pegmatites intruding mafic and carbonate-bearing sequences. Pegmatites associated with granitic domes within the Archaean Yilgarn Craton intruding ultramafic and mafic rocks contain red, orange and brown almandine garnet.
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In allusion to the pock-marked appearance of weathered surfaces of variolite, this term is derived from the Latin word, variola, for smallpox. Varioles are millimeter- to centimeter-scale, light-colored, globular to spherical structures, that are conspicuously observable within aphanitic, mafic igneous rocks, such as basalt, komatiite, and tachylite, that comprise either pillow lavas, subaerial lava flows, or volcanic dykes. Typically, they are less resistant to weathering than the enclosing aphanitic rock and, as a result, form pock-marks on the weathered surfaces of mafic rocks.Arndt, N., and Fowler A.D. (2004) Textures in komatiites and variolitic basalts.
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They are well exposed in Mount Serteng in Guyang granite- greenstone terrane. There are three sub-units in the greenstone sequence in this terrane. The lower layer is dominated by metamorphosed mafic and ultramafic volcanic rocks, with interlayered banded iron formation.Chen, L. (2007).
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The buoyancy of a microcontinent locally slows the rollback of and steepens the dip of subducting mafic lithosphere.Brun, J.-P., and Faccenna, C., 2008, Exhumation of high-pressure rocks driven by slab rollback: Earth and Planetary Science Letters, v. 272, p. 1-7.
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The mountain is an andesitic volcano. The volcano had a minor mud eruption in January 1914. In October 1949 the summit crater produced an ash cloud. The rock of the mountain is non-alkali mafic rock produced in the last 18,000 years.
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3750–3780 Ma) Nuvvuagittuq Supracrustal Belt, Québec (Canada). Earth Planet. Sci. Lett. 362, 283–293 (2013). The Nuvvuagittuq Greenstone Belt is part of a mafic unit called the Ujaraaluk unit, both of which are in the Inukjuak subprovince of the Minto Block.
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"Oldest rocks on Earth found". NBC News. Retrieved 2009-02-01.O'Neil, Jonathan; Carlson, Richard W.; Francis, Don; Stevenson, Ross K. (2008-09-26). "Neodymium-142 Evidence for Hadean Mafic Crust". Science 321 (5897): 1828-1831\. . though the dating methods are disputed.
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The field has erupted alkali basalt, basanite and hawaiite. Phenocrysts include clinopyroxene, olivine and plagioclase. There are also xenoliths including dunite, gabbro, granite, and notably ultramafic to mafic xenoliths. The rock composition has not changed much during the history of the Cima volcanoes.
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Ingólfsfjall consists mostly of mafic and metamorphic rocks (palagonite) and has its origin in subglacial eruptions which turned in the end subaerial and produced some lava at its top. Ari Trausti Guðmundsson, Pétur Þorleifsson: Íslensk Fjöll. Gönguleiðir á 151 tind. Reykjavík 2004, p.
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Chemical weathering alters the minerals constituent of rock surface. Decomposition of mafic and opaque minerals releases ions and colloids of iron, magnesium, calcium and sulphur. Alteration of feldspars and feldspathoids releases silica colloid. These materials are reached and transported by surface water.
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This obducted sequence of ultramafic to mafic rocks is the Semail Ophiolite complex. The ophiolite is locally rich in copper and chromite orebodies.Guilbert, John M. and Charles F. Park, Jr., 1984, The Geology of Ore Deposits, Freeman, p. 380-382 Dilek, Yildirim; et.
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Kuroko Massive Sulfide Cross section VMS deposits associated with bimodal sequences where felsic rocks are in greater abundance than mafic rocks with only minor sedimentary rocks. The Kuroko deposits, Japan; Buchans deposits, Canada; and Skellefte deposits, Sweden are classic districts of this group.
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The Devil's Inkpot lava flows formed from a fissure around the same time as the Sister's Peak region 829,000 years ago. Bentmoreite scoria cones record evidence of mafic volcanism, although older rhyolite and trachyte flows, domes and pyroclastic deposits point to felsic eruptions as well.
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Its pyroclastic deposits are remnants of explosive volcanism. The oldest exposed rocks within the belt are fine to medium-grained basalts and andesites. Lava flow units range in thickness from to . Mafic agglomerate and breccia are relatively abundant, being either massive and undeformed, or sheared.
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"Magma flow revealed by magnetic fabric in the Okavango giant dyke swarm, Karoo igneous province , northern Botswana." Journal of Volcanology and Geothermal Research 170, no. 3 (2008): 247–261. The Jurassic dykes were formed approximately 179 million years ago, composed of mainly tholeiitic mafic rocks.
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Fogelin is an assumed S-type asteroid, in line with the overall spectral type seen among Eunomian asteroids. Near-IR spectroscopy at the NASA Infrared Telescope Facility with the SpeX instrument showed that the asteroid contains mafic minerals, which are rich in magnesium and iron.
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The granitic domes are mostly TTG or TTG-like (tonalite-trondhjemite-granodiorite) in composition. The greenstone belts are interpreted as altered komatiitic basalts and volcanosedimentary rocks. These rocks range from ultramafic, mafic, and felsic in composition. Ultramafic rocks such as dunites can also be found.
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The Fennell zone is located approximately 500m further north and is hosted in a carrot-shaped granitoid plug hosted in andesitic and mafic meta-volcanics. The free gold is contained within narrow low-angle quartz-scheelite veins which locally extend into the country rock.
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Ma Wan surface rocks are mostly volcanic rocks called Yim Tin Tsai Formation. This is a coarse ash crystal tuff containing lapilli. Some layers of fine volcanic ash are found in the far north of the island. The contained mafic minerals are biotite and amphibole.
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The archaic term epidiorite is sometimes used, especially in Europe, to refer to a metamorphosed ortho-amphibolite with a protolith of diorite, gabbro or other mafic intrusive rock. In epidiorite the original clinopyroxene (most often augite) has been replaced by the fibrous amphibole uralite.
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Escalante and Sairecabur have erupted dark andesites, and later also dacites. Mafic enclaves are found in the post- caldera lavas. The colour of the rocks is black, brown or gray. Minerals include amphibole, biotite, bronzite, -containing augite, clinopyroxene, hornblende, magnetite, orthopyroxene, plagioclase, pyroxene and quartz.
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Macusani volcanics are primarily rhyolitic in terms of composition. Basaltic lava flows in the Picotani area are the only mafic volcanics. Their matrix is heavily altered to clay while phenocrysts are mostly preserved. Unusual minerals found in the volcanics include andalusite, muscovite, sillimanite and tourmaline.
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Silicate lavas can be classified into three chemical types: felsic, intermediate, and mafic (four if one includes the super-heated ultramafic). These classes are primarily chemical; however, the chemistry of lava also tends to correlate with the magma temperature, viscosity and mode of eruption.
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The Rio Moctezuma and its tributary Rio Tepache flow through the area. Lava flows have repeatedly impounded the Moctezuma river and dammed it. Rocks erupted in the field are basaltic andesite and hawaiite. These rocks are mafic and often hypersthene, nepheline or quartz normative.
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The Qabri Bahar complex formed in the Paleoproterozoic through the Mesoproterozoic with mafic and granitoid rocks, as well as rocks metamorphosed up to granulite grade in the sequence of metamorphic facies. Some geologists propose that the Qabri Bahar complex may preserve rocks from before the Pan-African orogeny. Major Event II, more than 700 million years ago, marked deformation, partial melting (also known as anataxis) and rocks metamorphosed up to amphibolite grade. Major Event III happened 700 to 640 million years ago, bringing crustal thinning and extension, mafic volcanism in the Abdulkadir complex and Mait complex, regional heating, metamorphism and the emplacement of gabbro and syenite through the thinned crust.
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The three largest plateaus, the Caribbean, Ontong Java, and Mid-Pacific Mountains, are located on thermal swells. Other oceanic plateaus, however, are made of rifted continental crust, for example the Falkland Plateau, Lord Howe Rise, and parts of Kerguelen, Seychelles, and Arctic ridges. Plateaus formed by large igneous provinces were formed by the equivalent of continental flood basalts such as the Deccan Traps in India and the Snake River Plain in the United States. In contrast to continental flood basalts, most igneous oceanic plateaus erupt through young and thin () mafic or ultra-mafic crust and are therefore uncontaminated by felsic crust and representative for their mantle sources.
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The Qabri Bahar Complex formed in the Paleoproterozoic through the Mesoproterozoic with mafic and granitoid units, as well as rocks metamorphosed to granulite grade (part of the concept of metamorphic facies). Some geologists propose that the Qabri Bahar complex may preserve rocks from before the Pan-African orogeny. Major Event II, more than 700 million years ago, marked deformation, partial melting (also known as anataxis) and rocks metamorphosed up to amphibolite grade. Major Event III happened 700 to 640 million years ago, bringing crustal thinning and extension, mafic volcanism in the Abdulkadir complex and Mait complex, regional heating, metamorphism and the emplacement of gabbro and syenite through the thinned crust.
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The Slave Craton (also known as the Slave Province) is smaller than the vast neighboring Superior Province, which extends southward to the Great Lakes. By contrast with the Superior Province, the Slave Province has more sedimentary rocks, more felsic than mafic rocks, more potassium-rich granite and gold and base-metal mineralization. Geologists have inferred ancient sea floor spreading in the western part of the province from dikes and mafic lava flows, overlain by deep ocean turbidite deposits. These rocks are believed to be the remains of oceanic crust that ended up preserved, surrounded on all sides by felsic volcanic rocks and granitoid plutons.
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Part of a stretch of shield volcanoes in Oregon with an unusually low elevation, meaning they have undergone less erosion over time than surrounding volcanic centers, Olallie has been excavated by glacial erosion on its northeastern flank. Its central volcanic plug has also been exposed. Comparisons of its morphology with Mount Jefferson suggest an age for the butte between 70,000 and 100,000 years; there is no evidence that it has erupted within the past 25,000 years. Olallie Butte has a steep, conical shape that serves as a transitional morphology between steep, mafic (rich in magnesium and iron) volcanoes like Mount McLoughlin and Mount Thielsen and flatter, mafic shields.
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The Precambrian oval-shaped Kanichee layered intrusive complex is the largest of many sill-like mafic-ultramafic bodies in felsic and mafic metavolcanic rocks in the northern portion of the Temagami greenstone belt.Geology and petrogenesis of the Kanichee layered complex, Ontario It comprises five magmatic series, each of which contains one or more types of igneous rock. A succession of cumulus phases comprising every magmatic series suggests that the Kanichee layered intrusive complex is south- facing, including the surrounding metavolcanic lava flows. This record indicates that magmatic rocks of the Kanichee layered intrusive complex originally formed in a level position and most likely very shallow beneath the Earth's crust.
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The plume magmatism theory is based on observations that most large igneous provinces include both hypabyssal and surficial manifestations of voluminous mafic magmatism within the same temporal period. For instance, in most Archaean cratons, greenstone belts correlate with voluminous dike injections as well as usually some form of larger intrusive episodes into the crust. This is particularly true of a series of ultramafic-mafic layered intrusions in the Yilgarn Craton of ~2.8 Ga and associated komatiite volcanism and widespread tholeiitic volcanism. Plume magmatism is an effective mechanism for explaining the large volumes of magmatism required to inflate an intrusion to several kilometres thickness (up to and greater than ).
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Vein orientation is preserved from original rock, but minerals within are mostly replaced by pyrite. With decreasing depth, selvages widen (10 cm - 1m) and contain more quartz and pyrite. Outside of selvages, most alteration occurs in replacement of mafic minerals by chlorite and of plagioclase by sericite.
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Accessed 8.24.2011 It has a wide-ranging natural habitat. In the Southeastern United States it is most often found in rocky forests, in both moist and dry soil, often associated with calcareous or mafic substrates. In the Midwest, habitats include forests, savannas, prairies, glades, and sand dunes.
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Lesher, C.M., Arndt, N.T., and Groves, D.I., 1984, Genesis of komatiite-associated nickel sulfide deposits at Kambalda, Western Australia: A distal volcanic model, in Buchanan, D.L., and Jones, M.J. (Editors), Sulphide Deposits in Mafic and Ultramafic Rocks, Institution of Mining and Metallurgy, London, p. 70-80.
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It is likely that the injection of new mafic magma into the previous magma chamber triggered this eruption. The lava flows were erupted about 7.3 ± 0.1 million years ago, after the Toba 1 eruption. A further small ignimbrite named Morro II has been linked to Negra Muerta.
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In igneous petrology an intermediate composition refers to the chemical composition of a rock that has 52-63 wt% SiO2 being an intermediate between felsic and mafic compositions. Typical intermediate rocks include andesite, dacite and trachyandesite among volcanic rocks and diorite and granodiorite among plutonic rocks.
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Kambalny () is a stratovolcano located in the southern part of Kamchatka Peninsula, Russia. It is the southernmost active volcano of Kamchatka. It has erupted mafic rocks. It has a summit crater as well as five cinder cones on its flanks which are the source of lava flows.
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Miño Volcano is a symmetrical cone-shaped stratovolcano located in El Loa Province, Antofagasta Region, Chile. It lies a few kilometres northwest of Aucanquilcha volcano and at its foot originates Loa River. The major settlement in its vicinity is Ollagüe. The volcano has erupted mafic andesite.
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Eclogites typically result from high to ultrahigh pressure metamorphism of mafic rocks at low thermal gradients of < as they were subducted to the lower crust to upper mantle depths in a subduction zone. They are generally formed from precursor mineral assemblages typical of blueschist-facies metamorphism.
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These mountain ranges are represented the three types of rocks: metamorphic, sedimentary and igneous. The granites geochemically include calc-alkaline granites with alkaline, meta-aluminous to peraluminous more abundant and monzogranites granites. Granodiorites, leucogranites and tonalites are also present. Mafic enclaves, dikes including lamprophyres, pegmatites and aplites.
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With an area of , the Ungava magmatic event caused the formation of a large igneous province.2000 Ma large mafic magmatic events Magmatic features that were formed during the Ungava magmatic event include the Klotz, Maguire and Senneterre dikes of Quebec and the Nipissing sills of Ontario.
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Conybeare Morrison, Prospect Hill Conservation Management Plan, Holroyd City Council, 2005Jones, I., Verdel, C., Crossingham, T., and Vasconcelos, P. (2017). Animated reconstructions of the Late Cretaceous to Cenozoic northward migration of Australia, and implications for the generation of east Australian mafic magmatism. Geosphere, 13(2), 460-481.
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27 Based on an average of 52 samples, the Orienta Sandstone is composed of: 33.3% nonundulatory quartz, 29.7% undulatory quartz, 17.3% potassium feldspar and 9.4% silicic volcanic clasts. Smaller constituents are 3.9% polycrystalline quartz, 2.3% opaques, 1.6% mafic volcanic clasts, 0.9% metamorphic, 0.7% sedimentary, and 0.4% plagioclase.
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The Cerro Morado volcanic field is located in northwestern Argentina, in the Jujuy Province. The town of is located within the volcanic field. The frontier with Chile lies approximately west of the volcanic field. The Altiplano and the adjacent southern Puna has experienced mafic volcanism during the Cenozoic.
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Le Gall, Bernard, Gomotsang Tshoso, Jérôme Dyment, Ali Basira Kampunzu, Fred Jourdan, Gilbert Féraud, Hervé Bertrand, Charly Aubourg, and William Vétel. "The Okavango giant mafic dyke swarm (NE Botswana): its structural significance within the Karoo Large Igneous Province." Journal of structural geology 27, no. 12 (2005): 2234–2255.
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Felsic magma or lava is higher in viscosity than mafic magma/lava. Felsic rocks are usually light in color and have specific gravities less than 3. The most common felsic rock is granite. Common felsic minerals include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars (albite- rich).
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Mapping of artisanal workings within the northwest quadrant of the tenement identified a quartz vein up to 1m wide within an easterly striking shear zone dipping to the north at 40°. The vein is hosted by sheared mafic volcanics and had been excavated over an estimated distance of 100m.
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Rojo Sur erupted undifferentiated mafic magmas. Its lead isotope composition is different from the composition of that segment of the Andes, being non- radiogenic. This isotope signature may be the effect of assimilation of deeper basement rocks during magma formation. In addition, the magmas are rich in incompatible elements.
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173–150 Ma, had similar composition with those produced in Triassic. The Cretaceous units are well exposed on Hainan Island. It can be divided into five stratigraphical units according to the geological sequence. The rocks were mainly igneous in nature, including granites, andesites, dacites, rhyolites, mafic dykes, etc.
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Mafic-felsic magma sequences ( thick) on the western edge of the Congo Craton are similar to those of the Paraná and Deccan LIPs, but in the Congo Craton the magma source became shallower with time. There was no geodynamic activity along the western Congo margin during the Mesoproterozoic.
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TES identified a large (30,000 square-kilometer) area that contained the mineral olivine. Olivine was found in the Nili Fossae formation. It is thought that the ancient impact that created the Isidis basin resulted in faults that exposed the olivine. Olivine is present in many mafic volcanic rocks.
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Cerro Tujle (also known as Cerro Tucle or Cerro Tugle) is a mafic volcanic centre in the Central Volcanic Zone of the Andes, Chile. It forms a deep maar. Its eruption products are aphyric. Previously in 1977, this crater has been identified as a meteor crater with diameters of .
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The region is dominated by Mesozoic-to-Cretaceous aged rocks which make up an uplifted subduction zone accretionary wedge called the Franciscan Complex. This unit is made up of sandstones, shales, cherts, metagraywackes, melanges, as well as mafic volcanics, and is mostly metamorphosed to blueschist and eclogite facies.
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La Negrillar is a volcanic cone and associated lava flow in Chile. It covers on the southwestern margin of the Atacama basin. It erupted basalts and andesite and its flows and cones are well preserved. It is one of several mafic centres in the region located along fault systems.
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It is sometimes classified as a mineraloid. Though obsidian is usually dark in color, similar to mafic rocks such as basalt, obsidian's composition is extremely felsic. Obsidian consists mainly of SiO2 (silicon dioxide), usually 70% by weight or more. Crystalline rocks with a similar composition include granite and rhyolite.
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It led to the partial melting of the lower crust and mantle wedge. It produced a large amount of magma, which formed granitoids, greenstone, mafic and felsic volcanic rocks. As subduction continued, the region next to the arc spread and formed a back-arc basin. Thus, magma flowed upward.
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The Ljusdal Batholith is a group of plutons in central Sweden formed during the Svecofennian orogeny. The batholith occupies a NW-SE elongated area of c. 130 x 100 km covering most of Hälsingland. The Ljusdal Bathoilith is mostly made up of granitoids with lesser amounts of mafic intrusions.
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Coyoteite has been found only in the mafic alkalic diatreme at the Coyote Peak near Orick, Humboldt County, California, US. It is formed in pegmatitic clots associated with some rare iron sulfide minerals, such as erdite, bartonite and djerfisherite, as well as with common minerals pyrrhotite and magnetite.
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There is a chain of Pleistocene cinder cones east of the butte that trends from northwest to southeast, with other Pleistocene cinder cones located to the south. There is also a mafic, well-preserved cinder cone above the Green Ridge fault zone, which produced a Pleistocene lava flow.
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The El Tatio ignimbrite ponded in the Tatio graben and may have originated at the Tocorpuri rhyolite dome, which is less than one million years old, in a vent now buried beneath the El Tatio volcanic group, or at the Laguna Colorada caldera. The El Tatio volcanic group has likewise been dated to be less than one million years old, and its lavas overlie the older formations. Volcan Tatio erupted mafic lavas probably during the Holocene; later this volcano was reinterpreted to be of Pleistocene age. Petrological data suggest that over time the erupted lavas of the El Tatio volcanic group have become more mafic, with older products being andesitic and later ones basaltic-andesitic.
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The highest assessment was of gold per ton and 0.99% of nickel over , both from the same zone. Detailed work did not occur in the Rib Lake area of southern Gillies Limit Township and northern Best Township until 1968, when mapping took place, but it is unclear whether volcanic rocks in the Rib Lake area are part of the TGB, as they have not been mapped in any detail. With the existence of Early Archean age tholeiitic and/or calc-alkaline mafic to intermediate volcanic rocks, they may represent a minor continuation of the belt, which is located about to the southwest. Small intrusions and pyroclastics of mafic composition are also present in the area.
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Thomas J. Goreau et al who wrote the book Geotherapy believe that mafic/ultra-mafic rock flour has a powerful effect in restoring trace minerals to soils, which increases the health and vigour of the Microorganism, Plantae, Animalia pathway and also sequesters carbon. An early experimenter was the German miller, Julius Hensel, author of Bread from Stones, who reported successful results with steinmehl (stonemeal) in the 1890s. His ideas were not taken up due to technical limitations and, according to proponents of his method, because of opposition from the champions of conventional fertilisers. John D. Hamaker argued that widespread remineralization of soils with rock dust will be necessary to reverse soil depletion by current agriculture and forestry practice.
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If the mafic lithosphere on either side of the microcontinent continues to roll back, a buoyant portion of the microcontinent may detach, allowing the retarded portion of the mafic slab to roll quickly back, making room for the UHP continental crust to exhume and driving back-arc extension. This model was developed to explain repeated cycles of subduction and exhumation documented in the Aegean and Calabria–Apennine orogens. UHP exhumation by slab rollback has not yet been extensively explored numerically, but it has been reproduced in numerical experiments of Apennine-style collisions.Faccenda, M., Gerya, T. V., and Burlini, L., 2009, Deep slab hydration induced by bending-related variations in tectonic pressure: Nature Geoscience, v.
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In addition, NASA reported the rover found two principal soil types: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic type, similar to other martian soils and martian dust, was associated with hydration of the amorphous phases of the soil. Also, perchlorates, the presence of which may make detection of life-related organic molecules difficult, were found at the Curiosity rover landing site (and earlier at the more polar site of the Phoenix lander) suggesting a "global distribution of these salts". NASA also reported that Jake M rock, a rock encountered by Curiosity on the way to Glenelg, was a mugearite and very similar to terrestrial mugearite rocks.
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The Manfred Complex is a heavily attenuated and discontinuous series of ultramafic to mafic cumulates contained within a matrix or wall-rocks of mixed Dugel and Meeberrie Gneisses. The rock types are primarily pyroxene gabbro to amphibolite, with rare serpentinised peridotite and dunite, occasionally containing relict igneous or metamorphic olivine. These boudins of material range from centimetre-scale to ~100m thick and one kilometre long and, based on their position within anticlines and synclines in the Mount Narryer area, are interpreted to have intruded subparallel to bedding and are now strung out by shearing. The Manfred Complex is interpreted to represent an early Archaean mafic to ultramafic layered intrusion which has been disaggregated.
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Burroughs Mountain, situated at the northeast foot of Mount Rainier, WA, exposes a large-volume (3.4 km3) andesitic lava flow, up to 350 m thick and extending 11 km in length. Two sampling traverses from flow base to eroded top, over vertical sections of 245 and 300 m, show that the flow consists of a felsic lower unit (100 m thick) overlain sharply by a more mafic upper unit. The mafic upper unit is chemically zoned, becoming slightly more evolved upward; the lower unit is heterogeneous and unzoned. The lower unit is also more phenocryst-rich and locally contains inclusions of quenched basaltic andesite magma that are absent from the upper unit.
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In addition, NASA reported that the Curiosity rover found two principal soil types: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic type, similar to other martian soils and martian dust, was associated with hydration of the amorphous phases of the soil. Also, perchlorates, the presence of which may make detection of life-related organic molecules difficult, were found at the Curiosity rover landing site (and earlier at the more polar site of the Phoenix lander) suggesting a "global distribution of these salts". NASA also reported that Jake M rock, a rock encountered by Curiosity on the way to Glenelg, was a mugearite and very similar to terrestrial mugearite rocks.
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The city lies within the Sidlaw-Ochil anticline, and the predominant bedrock type is Old Red Sandstone of the Arbuthnott-Garvock group.; Differential weathering of a series of igneous intrusions has yielded a number of prominent hills in the landscape, most notably the Dundee Law (a late Silurian/early Devonian Mafic rock intrusion) and Balgay hill (a Felsic rock intrusion of similar age). In the east of the city, in Craigie and Broughty Ferry, the bedrock geology is of extrusive rocks, including mafic lava and tuff. The land surrounding Dundee, particularly that in the lower lying areas to the west and east of the city, bears high quality soil that is particularly suitable for arable farming.
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The region is the site of the Miocene Altiplano-Puna volcanic complex, one of the world's largest ignimbrite province. The rocks erupted in the complex are derived from the crust and the mantle in equal amounts. A number of mafic volcanic fields and isolated cones are found in the northern Puna.
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These lavas are primarily aphyric basalts, are grayish in color, trachytic in texture and composed of olivine. Other basalts contain olivine and pyroxene phenocrysts. To the west are a few mafic porphyritic basalts and possibly older Miocene basalts cut by dykes and faults. Olivine nephelinite has been collected near these basalts.
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The island of Curaçao began to form within the past 145 million years, beginning in the Cretaceous, as part of the Lesser Antilles island arc. Because the island was submerged for large parts of its history, reef environments formed atop thick layers of mafic volcanic rock, producing carbonate sedimentary rocks.
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Intrusive rocks: Many intrusive bodies of mafic to granitic composition, with ages varying from early Triassic to Late Cretaceous, have been identified in Iran (e.g., Borujerd–Shamsabad axis). In Triassic–Jurassic, volcanic rocks predominated the plutonic rocks. They are mainly alkaline in nature and are more abundant in Sanandaj–Sirjan.
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The Changchun Schist being mostly greenschist is found on the western side and forms thick beds. It is found along with smaller amounts of chert, and black schist. The rock is foliated dark green rock containing chlorite, epidote, quartz, calcite, biotite, albite and actinolite. They are derived from mafic volcanic rocks.
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The Espíritu Santo Fault places Precambrian metamorphic rocks to the south against Paleozoic metamorphic rocks to the north. The fault displaces rocks of the Puquí Complex, Valdivia Group, and mafic and ultramafic rocks and sediments of the Bajo Cauca. The Santa Rita Fault terminates against the Espíritu Santo Fault.Paris et al.
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Coreopsis latifolia is native to the Blue Ridge Mountains, its distribution extending from the Great Craggy Mountains to the South Carolina line. Populations in Tennessee are disjunct. The plant grows in moist hardwood forest habitat on mafic rock such as amphibolite or hornblende gneiss. It can sometimes be seen on roadsides.
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In geology an enclave is an aggregate of minerals or rock observed inside another larger rock body. Usually it refers to such situations in plutonic rocks. Micro-granular enclaves in felsic plutons result from the introduction of mafic magma into the magma chamber an its subsequent cooling following incomplete mixing.
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The source of heat for the volcanoes and geothermal field is unclear: both deep mafic and shallow felsic sources have been proposed. Seismic tomography of the area below the Salton Buttes has identified areas in the mantle with an anomalously low seismic velocities, which would be consistent with higher temperatures there.
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The Duluth Complex is one of the largest intrusions of gabbro on earth,Schwartz & Thiel (1963), p. 114. and one of the largest layered mafic intrusions known. It covers an area of 4715 km2.Guilbert, John M. and Charles F. Park, Jr., The Geology of Ore Deposits, Freeman, 1986, pp.
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Tephriphonolite is a mafic to intermediate extrusive igneous rock in composition between phonotephrite and phonolite. It contains 9 to 14% alkali content and 48 to 57% silica content (see TAS diagram). Tephriphonolite has been found, for example, at Colli Albani volcano in Italy and in the Asunción Rift of Paraguay.
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The soils are mostly well-drained, with medium brown or dark reddish brown sandy loam topsoils. The subsoils are clay loam or clay; they are medium red or dark red. The darker soils, which support higher plant diversity, have developed on mafic rock; the medium-toned soils are on felsic rock.
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This tectonic grain, including the 2.62 Ga Oregon Trail structure, controlled the locations and orientations of Proterozoic rifting and uplifts related to the Laramide orogeny. If there has been any net crustal growth of the Wyoming Province since 3.0 Ga, it has involved a combination of mafic underplating and arc magmatism.
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A coin added for scale. Eclogite () is a metamorphic rock formed when mafic igneous rock is subjected to high pressure. Eclogite forms at pressures greater than those typical of the crust of the Earth. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth.
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This is possibly from the Rheic Ocean. Finally, above this are other schists called the schistose domain of Galicia-Trás-os-Montes or Para-autochthenon. There are five oval shaped masses of mafic to ultramafic rocks making up the ophiolite. These are the Cabo Ortegal, Ordes, Lalín, Bragança and Morais Massifs.
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Lava extruded from the volcano is primarily trachydacite to trachyandesite in composition, transitioning from more andesitic to more dacitic compositions over time. The magma is likely a mix from three different sources, a rhyodacite source, a dacite source (likely itself a mixture of rhyodacite and basalt), and a mafic source.
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For example, in the southern Appalachians, high-elevation outcrops, composition gradients are a function of elevation, potential solar radiation, geographic gradient that corresponds to broad geological differences (mafic rocks to the northwest vs. felsic rocks in the southwest direction), and surficial geomorphology (bedrock surfaces that are less fractured in the southeast).
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Pyroclastic plateaus are produced by massive pyroclastic flows and they are underlain by pyroclastic rocks: agglomerates, tephra, volcanic ashes cemented into tuffs, mafic or felsic. Pyroclastic plateaus are also called ignimbrite plateaus. Examples include Shirasu-Daichi which covers almost all of Southern Kyūshū, Japan and the North Island Volcanic Plateau in New Zealand.
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Little work has been completed in this area. In 1959 and 1960, Goldfields Mining conducted a basic airborne electromagnetic survey and magnetic survey over the property. Several holes were drilled and intersected mostly mafic to intermediate volcanic rocks and areas of stringer sulfides with pyrrhotite, pyrite and some chalcopyrite. No assays were reported.
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The Kasai-Lomami group has two rock units. One is a mafic unit with gabbro, norite, amphibolite and anorthosite. Taken together, they are the remains of magma intrusions metamorphosed to granulite grade. The second unit contains dark gneiss and aluminium-rich granulite, which may have originated from sediments, along with metadolerite dikes.
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The 13-million-year-old mafic dike swarms in the Bella Bella area were formed by the Anahim hotspot when this part of North America was directly overhead. The dikes are believed to mark the first arrival of the hotspot, although it is now located in central British Columbia at Nazko Cone.
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Biotite is generally of low content and the main mafic minerals are clinopyroxene (±) and amphibole (±). The macroscopic colour is grey, being little darker than granite. There is high-grade metamorphic rock originated from nepheline syenite that is characterized by gneiss texture of very rare occurrence. It is called nepheline syenite gneiss or litchfieldite.
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In the Adamsfield area The Ragged Basin Complex is a broken up formation of chert, sandstone, red mudstone and mafic magma derived rocks. The sandstone is derived from metamorphic and volcanic fragments. Ultramafic rocks are serpentinised. They are not ophiolites, but instead are cumulates of heavy minerals in a shallow magma chamber.
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Pirurayo has erupted andesite and dacite, which belong to the potassium-rich volcanics series. They probably formed from a mafic magma, which underwent assimilation of crustal materials and fractional crystallization. Volcaniclastic rocks from Pirurayo form part of the regional Moreta formation. Volcanic activity occurred between 28 ± 3 and 20 ± 2 million years ago.
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Schmidt, Regional and local patterns of low-grade metamorphism (2008), Abstract; Green, Volcanic and Sedimentary Rocks (2004), p. 52. These volcanics created the "roof rocks" into which were emplaced the mafic formations of the Duluth Complex. Primarily formed after 1102 mya,Green, Volcanic and Sedimentary Rocks (2004), p. 52; Naldrett (2004), pp.
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The region is at an elevation of above sea level, with gently undulating terrain of rounded hills sculpted by glacial action. The general drainage direction in the area is towards the north or east. The bedrock is mafic or intermediate metavolcanic rock. The area has unusually elevated levels of copper, cadmium and zinc.
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The effect of bedrock on soil and ecology. Ultramafic rock (left) and mafic rock (right). New Zealand has many natural disturbances to its environment which endemic species have evolved to tolerate. These include local events with short return times like landslides, floods, el nino and fires (rare before the arrival of humans).
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Mount Asahi is formed from non-alkaline mafic rock from the middle to late Miocene. Non-alkaline rock from pyroclastic flows in the late Miocene to early Pliocene are also present. The flanks of the mountain include accretionary complex of Permian basalt block and a melange mix of late Jurassic to early Cretaceous.
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Rhyolite flows, breccias and hyaloclastics are the primary rocks comprising the Flat Landing Brook Formation. Locally abundant rocks include tholeiitic to transitional mafic fragmental rocks and massive flows, as well as felsic tuffs, tholeiitic pillow basalts and minor porphyritic felsic flows. Siltstone, greywacke, iron formation, ferromanganiferous shale and chert represent minor rocks.
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Baddeleyite was first found in Sri Lanka in 1892. It can be found in numerous terrestrial and extraterrestrial rocks. Some of these terrestrial rocks are carbonatite, kimberlite, alkaline syenite, some rocks of layered mafic intrusions, diabase dikes, gabbroid sills and anorthosite. Some examples of extraterrestrial rocks are tektites, meteorites and lunar basalt.
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These so-called Lateorogenic granites are distinguished by usually containing garnet and cordierite and being accompanied by rather few rocks of mafic and intermediate composition. Scattered small granitoids crop out within the same zone. Formed 1810–1770 million years ago, these are the youngest granitoids in southern Finland associated with the Svecofennian orogeny.
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Chromite minerals are mainly found in mafic-ultramafic igneous intrusions and are also sometimes found in metamorphic rocks. The chromite minerals occur in layered formations that can be hundreds of kilometres long and a few meters thick. Chromite is also common in iron meteorites and form in association with silicates and troilite minerals.
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Hope Bay Gold Mine, main camp area Hope Bay Gold Mine, tailing pond The Hope Bay greenstone belt, also called the Hope Bay volcanic belt, is a long Archean greenstone belt in western Nunavut, Canada. It consists of mostly mafic volcanic rocks and contains three major gold deposits called Boston, Doris and Naartok.
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The composition of Luingo magmas has been modelled. The closest correspondence is obtained by assuming the mixing crustal material with mafic magmas in a ratio 1:4. Subsequently, the crust became thicker in the region, thus the Galan ignimbrites formed from magmas where the crustal material:mafic magma ratio is about 1:1.
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Havilah Resources NL. (2006) Third Quarter Activities and Cash Flow Report The Wynbring area, a large part of the western Fowler Domain, covers approximately 2,000 square kilometres and consists of fractures that may include intrusion of mafic-ultramafic bodies with potential for nickel sulfides, chromite and platinoids. Exploration and regional drilling near the northern end of the Fowler Domain and within the Harris Greenstone Belt has identified numerous large mafic and ultramafic bodies which have the potential to host nickel sulfide mineralisation. Ultramafic intrusive rock hosting nickel bearing sulfides (pentlandite and mackinawite) have returned values up to 0.49% nickel, 38 parts per billion (ppb) platinum and 58 ppb palladium. Previous explorations reported up to 0.74% nickel from samples obtained in shallow bedrock drilling.
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Subsidiary magma chambers which developed beneath the northwestern and southeastern flank gave rise to the La Celosa and Ch'aska Urqu volcanic centres, respectively. These subsidiary pathways also allowed basaltic andesite magmas to ascend to the surface; the main magma chamber would have intercepted any mafic magmas ascending into the central vent as such mafic magmas are denser. The walls of the magma chamber were also affected by strong hydrothermal alteration processes, with weaker alteration also occurring in the walls of the subsidiary magma chambers. La Poruñita was probably formed by magmas from the floor of the main magma chamber, or from the magma that enters the magma chamber from below; it had already undergone some crustal contamination in the depths of the crust when it erupted.
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Several other prominent gravity and magnetic highs are arranged along the Mugrave Block strike line, one of which was drilled by BHP in the 1990s through 300m of Permian glacial sediments. This caldera is composed of highly tectonised, stretched felsic volcanic rocks, interleaved with a significant thickness of equally sheared titaniferous differentiated mafic sills. The best interpretation of this, and probably also of the Palgrave Caldera is that they represent hot spots along the Musgrave Block where significant magma flux penetrated, formed volcanic calderas with large subvolcanic granite intrusions, and associated mafic volcanism. The relationship of the large granite calderas to the 1050-1080 Ma volcanics has been postulated as one in which the granite calderas were the source for the intermediate and felsic volcanic rocks.
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The origin of igneous rock, or petrogenesis , in continental arcs is more complicated than that in oceanic arcs. The partial melting of the subducting oceanic slab generates primary magma, which would be contaminated by the continental crust materials when it travels through the crust. Because the continental crust is felsic or silica while the juvenile primary magma is typically mafic, the composition of magmas in continental arcs is the product of mixing between igneous differentiation of mafic magmas and felsic or silica crust meltings. The mixing of existing continental crust, lower part of lithosphere or lithospheric mantle under the continental crust, the subducting oceanic crust and sediments, the mantle wedge and the underplates materials together is the main source of continental arc rocks.
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The BGB is contained within part of a larger system called the Barberton Granite Greenstone Terrain (BGGT) which includes two main components; the supracrustal succession, which defines the BGB portion, and the deeper-level intrusive units that surround the BGB. Major rock types found within the BGB are mafic to ultramafic volcanics, sedimentary, and shallow intrusive rocks covered by a thin sedimentary veneer. The deeper-level intrusive pluton units dome up under the greenstone belt and are divided into two major groups: the TTG group, (tonalite-trondhjemite-granodiorite) which consists of plagioclase dominant feldspar minerals and the GMS group (granite-monzonite-syenite), in which alkali feldspars are the dominant mineral composition. Pre-3.2 Ga, eruptions of mafic to ultramafic volcanics formed thick sequences.
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Other common minerals include quartz, orthoclase, talc, carbonate minerals and amphibole (actinolite). Greenschist is a general field petrologic term for metamorphic or altered mafic volcanic rock. In Europe, the term prasinite is sometimes used. A greenstone is sometimes a greenschist but can also be rock types without any schistosity, especially metabasalt (spilite or picrite).
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Located in the western limb of the Western Ranges of the Colombian Andes. The fault puts Cretaceous mafic igneous rocks to the east in contact with Tertiary marine sedimentary rocks to the west. The fault cuts mud flows dated at about 10,000 to 15,000 years. It causes strong lineaments and offsets terraces and alluvial deposits.
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Caldwell, J., and P. Caldwell (2011) The Real Mount Sinai. Split Rock Research Foundation, Diamondhead, Mississippi. 60 pp. In contrast to the real Jabal al-Lawz, the summit of Jabal Maqlā consists mainly of dark-colored hornfels derived from metamorphosed volcanic rocks that originally were silicic and mafic lava flows, tuff breccias, and fragmental greenstones.
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El Rojo Norte is a cinder cone in the Andes, constructed on top of volcano debris in the Lauca basin. The cone is high and wide at its foot. Its profile has been reduced by erosion; the cone sits on an andesitic mound. A lava flow containing mafic andesite is associated with the cone.
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It is an andesitic stratovolcano. The peak consists of non-alkali mafic rocks, dating from the Early Pleistocene overtop of non-alkali felsic rocks from the Late Miocene-Pliocene. Several smaller islets surround Ko Island, including Daihiyakushima, Shohiyakushima, Tenjinshima, and Sazaeshima. To provide refuge for fishing vessels, a small harbor has been put in place.
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The Albemarle Group is a geologic group in North Carolina composed of metamorphosed mafic and felsic volcanic rock, sandstone, siltstone, shale, and mudstone. It is considered part of the Carolina Slate Belt and covers several counties in central North Carolina. It preserves fossils dating back to the Ediacaran period in the Floyd Church member.
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It was the most voluminous and included the Shamiram and Egvard subsidiary centres. The third phase (0.74–0.68 Ma) while similar to the second was more restricted in regional extent to the Mantash River basin. The fourth stage (0.56–0.45 Ma) involved mafic lava flows from parasitic vents in the southern parts of the volcano.
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Magnetite and biotite are also present. Generally, early rocks are mafic and the late ones intermediate or silicic. Magma mixing may have played a role in the formation of the rocks; specifically andesites formed from the mixing of basaltic-lamprophyric melts with dacitic-rhyolitic ones within andesitic rocks. Overall composition is potassium-rich calc- alkaline.
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VMS deposits associated with siliciclastic sedimentary rock dominated settings with abundant felsic rocks and less than 10% mafic material. These settings are often shale-rich siliciclastic-felsic or bimodal siliciclastic. The Bathurst camp, New Brunswick, Canada; Iberian Pyrite Belt, Spain and Portugal; and Finlayson Lake areas, Yukon, Canada are classic districts of this group.
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Ashikule and Tengchong have high ratios of to in their composition. isotope data indicate that in comparison with the volcanoes of the Tengchong area, Ashikule volcanoes formed by slower melting of rocks. The magmas of Ashikule probably did not form under the influence of water metasomatism. The ultimate source rocks may be mafic- ultramafic rocks.
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Figure 2a. Cross-polarized light photomicrograph showing garnet and biotite and plagioclase in the sample CV-126 from the mafic S-type Strathbogie Granite, Australia. Minor minerals in S-type granites reflect the aluminium saturation or ASI Index of the rock being greater than 1.1 mol%. These minerals include cordierite, muscovite, garnet, and sillimanite.
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Quartz is found only in the most strongly peralkaline rocks. Mafic minerals may include aegirine, fayalite, aenigmatite, ilmenite, and sodic amphibole (often arfvedsonite or ferrorichterite).White, J.C., Ren, M., and Parker, D.F., 2005, "Variation in mineralogy, temperature, and oxygen fugacity in a suite of strongly peralkaline lavas and tuffs, Pantelleria, Italy." The Canadian Mineralogist, vol.
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Accessory phase controls on the geochemistry of crustal melts and restites produced during water-undersaturated partial melting. Contributions to Mineralogy and Petrology, 114(4), 550–566. It is commonly formed from magmatism involving carbonatic melts but not mafic plutons or lavas. Those rocks usually host economic REE ore deposits, making monazite geochronology important in mining exploration.
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The geology of Mauritius and Rodrigues is comparatively recent. The oldest rocks on Mauritius are only 10 million years old and 1.54 million years old on Rodrigues Island. The mafic basalts of the two islands formed in relation to the hotspot that generated the Deccan Traps and coral reefs built on the volcanoes forming non-volcanic sediments.
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Angular unconformities of vastly differing magnitudes separate the Cardenas Basalt from the overlying Nankoweap Formation and Tonto Group. Mafic sills and dikes (basalt resp. diabase) intrude all rocks within Unkar Group members below the Cardenas Basalt. They consist of black, medium- to coarse- grained, olivine-rich basalt that contains plagioclase, olivine, clinopyroxene, magnetite-ilmenite, and biotite.
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Next is the lower volcanic unit, which is mostly pillow lava, breccia, and intrusive rocks. Metasediments of mostly mafic and intermediate tuffaceous composition are cut by dikes (intrusive rock). Below the lower volcanic unit is the dike complex. The dike complex has dacite and rhyolite dikes that cut into the rocks of the lower volcanic unit.
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Chalcopyrite occupies later fractures which intersect massive arsenopyrite. Sparse quartz veins normally exist in or adjacent to the arsenopyrite-rich zones. Several northeast-trending deformation zones intersect pyroxenite of a mafic sill in northwest Strathy Township. Within these high-strain zones quartz veins normally contain chalcopyrite, pyrite, pyrrhotite with exsolved pentlandite and traces of sphalerite and galena.
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63 no. 2 (1998), pp. 446–453. Around 1,269-1,267 million years ago, the Slave craton was partly uplifted and intruded by the giant Mackenzie dyke swarm, radiating from a mantle plume center west of Victoria Island. This was the last major event affecting the core of the Slave craton, although some younger mafic magmatic events affect its edges.
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Vale announced that they intersected mineralized sulfide zones ranging from to thick. In 1952 Rib Lake Copper Mines explored areas adjacent to Whitney Lake and between Whitney Lake and Rib Lake, by creating trenches and carrying out diamond drilling. Nickel was discovered with widespread pyrrhotite in sheared mafic rocks. Gold mineralization was discovered with pyrite in slightly siliceous tuff.
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Schematic representation of a metamorphic reaction. Abbreviations of minerals: act = actinolite; chl = chlorite; ep = epidote; gt = garnet; hbl = hornblende; plag = plagioclase. Two minerals represented in the figure do not participate in the reaction, they can be quartz and K-feldspar. This reaction takes place in nature when a mafic rock goes from amphibolite facies to greenschist facies.
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The Windimurra Igneous Complex is part of the c. 2813 Ma Meeline Suite of mafic- ultramafic layered intrusions of the central Murchison Domain, Yilgarn Craton of Western Australia. It is a conical body, approximately 7 km thick, primarily composed of layered gabbroic rocks, which intrude into c. 2820 Ma Norie Group rocks of the Murchison Supergroup.
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The confluence of Tryall Creek and Cooks Branch is in the Piedmont of Virginia in mafic and felsic metavolcanic rocks. Both tributaries arise in granite (Tryall Creek) or granite gneiss (Cooks Branch). Three Creek flows into the Coastal Plain in the Bacon Castle Formation and then for most of its length, especially the swampy areas it is in alluvium.
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Intrusions of both mafic and felsic character are also found. The whole massif is heavily faulted with some valleys such as Alva Glen and Glen Sherup having been eroded along these lines. Glacial till covers much of the lower ground around and within the range and peat accumulations occur on the plateau surface particularly in the west.
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Diamond Head, Hawaii, is an example of a tuff cone, as is the island of Ka'ula. The glassy basaltic ash produced in such eruptions rapidly alters to palagonite as part of the process of lithification.Macdonald 1983, pp.17-20 Although conventional mafic volcanism produce little ash, such ash as is formed may accumulate locally as significant deposits.
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Li, S.X., Sun, D.Y., Yu, H.F., Jin, W., Liu, X.S., Cao, L., 1995. Distribution of Ductile Shear Zones and Metallogenic Prediction of the Related Gold Deposits in the Early Precambrian Metamorphic Rocks, Middle-Western Inner Mongolia. Jilin Science and Technology Press, Changchun, pp. 1-111. Greenstones are sequences of Precambrian metamorphosed ultramafic to mafic rocks and sedimentary rocks.
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The Middle Allochthon is similar, but contains Neoproterozoic metasedimentary rocks, many of which show glacial origins. The Sarv Nappe—the highest thrust sheet—contains dolerite from 600 million years ago. The overlying Seve Nappe formed along a continent-ocean transition, with mafic and ultramafic meta- igneous rocks. These rocks were buried to a depth of 60 kilometers.
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The composition data indicate that Ollagüe was underpinned by a large magma chamber that was the source of the main edifice building andesite magmas. In this main magma chamber, differentiation processes generated the andesitic and dacitic magmas from basaltic andesite. The chamber itself was chemically zoned. Episodically, new mafic magmas were injected into the magma chamber from below.
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El Rojo Sur is a monogenetic volcano in the Andes, in the form of a cone. It is similar to El Rojo Norte farther north. A mafic andesite lava flow was erupted from the high cone that also features red scoria. Ages obtained by potassium-argon dating are 2.93±0.13, 3.4±0.4 and 3.23±0.12 mya.
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Relief Map of Mount Ōyama (Center) The mountain is made from non-alkali mafic rock. The rock is 7-15 million years old. The rock was extruded on the sea floor during the Neogene and then pushed up and onto the island of Honshu when the Izu-Bonin-Mariana Arc collided with the rest of Japan.
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Moraines are also found and reflect the past occurrence of glaciation on the mountain; they lie at around elevation. The volcano has erupted dacitic lavas containing andesitic mafic inclusions. These inclusions resemble those from the Soncor flow of neighbouring Lascar to the northeast. Some rocks may have been influenced by the interaction with calcium carbonate in the magma chambers.
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The island consists of mafic alkali and non-alkali volcanic rock, less than 18,000 years old. On the south side of the island at , there is a lighthouse and a heliport operated by Japan Coast Guard. Because of volcanic activity and nature conservation, landing on the island requires the approval of the Agency for Cultural Affairs.
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The Clisbako Caldera Complex (also called the Cheslatta Caldera Complex) is a large dissected caldera complex in the Chilcotin Group and Anahim Volcanic Belt in central British Columbia, Canada. It has a diameter of and is composed mainly of Eocene felsic and mafic volcanic rocks. Rocks within the caldera range in composition from basalt to rhyolite.
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If not all necessary elements are abundant, the mineral will not grow. When mapping the metamorphic grade of a terrane, a geologist has to take the lithology of the rock in account. Lithologies are mainly dependent on the protolith, the original rock before metamorphism. The main lithologies are ultramafic, mafic, felsic (or quartzo-feldspathic), pelitic and calcareous.
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Andy Burnham Transitional granulite- eclogite facies granitoid, felsic volcanics, mafic rocks and granulites occur in the Musgrave Block of the Petermann Orogeny, central Australia. Coesite- and glaucophane-bearing eclogites have been found in the northwestern Himalaya. The oldest coesite-bearing eclogites are about 650 and 620 million years old and they are located in Brazil and Mali, respectively.
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The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity. The crust of Earth is of two distinct types: # Oceanic: to thickStructure of the Earth. The Encyclopedia of Earth. March 3, 2010 and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro.
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The "Highland Flutes" lie between the moraine and the lake; the "Toimi Drumlin Field" is on the far side of the moraine, just west of the highlands. The North Shore Highlands therefore are composed of mafic outcroppings and volcanic ridges along the lakeshore overlain in places by a ground moraine, and an inland glacial moraine paralleling that shoreline.
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The massive Voisey's Bay nickel deposit is considered to have formed via a similar process. The process of forming nickel laterite deposits is essentially similar to the formation of gold laterite deposits, except that ultramafic or mafic rocks are required. Generally nickel laterites require very large olivine-bearing ultramafic intrusions. Minerals formed in laterite nickel deposits include gibbsite.
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The Von Damm vent field consists of talc mounds, which have exposed mafic or ultramafic rocks such as gabbros or peridotites containing the mineral olivine. Chimney structures at the Von Damm field are of varying shapes and sizes, but tend to also consist of talc precipitates. Green olivine mineral at an outcrop of the Von Damm vent field.
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Oceanic crust is denser because it has less silicon and more heavier elements ("mafic") than continental crust ("felsic"). As a result of this density stratification, oceanic crust generally lies below sea level (for example most of the Pacific Plate), while continental crust buoyantly projects above sea level (see the page isostasy for explanation of this principle).
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Mount McKay is a mafic sill located south of Thunder Bay, Ontario, Canada, on the Indian Reserve of the Fort William First Nation. It is the highest, most northern and best known of the Nor'Wester Mountains. It formed during a period of magmatic activity associated with the large Midcontinent Rift System about 1,100 million years ago.
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It also contains xenoliths both from Agua Dulce lavas and Paleozoic sediments. The Kumurana intrusion has a composition between granodiorite and quartz monzonite. Overall, the Kari-Kari rocks are peraluminous and originated from the amphibolite-granulite segment of the crust under the influence of magmatic underplating. Differentiation along mafic and peraluminous phases formed the eventual magma.
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Schematic representation of a metamorphic reaction. Abbreviations of minerals: act = actinolite; chl = chlorite; ep = epidote; gt = garnet; hbl = hornblende; plag = plagioclase. Two minerals represented in the figure do not participate in the reaction, they can be quartz and K-feldspar. This reaction takes place in nature when a mafic rock goes from amphibolite facies to greenschist facies.
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Because most Ni behaves as a compatible element in igneous differentiation processes, the formation of nickel-bearing sulfides is essentially restricted to sulfide saturated mafic and ultramafic melts. Minor amounts of Ni sulfides are found in mantle peridotites. The behaviour of sulfide melts is complex and is affected by Cu:Ni:Fe:S. Typically, above 1100 °C, only one sulfide melt exists.
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Pyrrhotite is a rather common trace constituent of mafic igneous rocks especially norites. It occurs as segregation deposits in layered intrusions associated with pentlandite, chalcopyrite and other sulfides. It is an important constituent of the Sudbury intrusion where it occurs in masses associated with copper and nickel mineralisation. It also occurs in pegmatites and in contact metamorphic zones.
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Extensional tectonics in the north led to mafic volcanic activity within the Shan-Thai Block in the Carboniferous, continuing into the Permian. Some red beds also formed during the same period. During the Permian, almost the entire region was submerged during a major marine transgression. Carbonates deposited in shallow, shelf seas and today form dramatic karst landscapes.
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Phonotephrite is a strongly alkaline volcanic rock with a composition between phonolite and tephrite. This unusual igneous rock contains 7 to 12% alkali content and 45 to 53% silica content (see TAS diagram). It can be described as a mafic phonolite or a potassic tephrite. Phonotephrite lava flows and volcanic cones have been identified in Antarctica (e.g.
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Tragia urticifolia, commonly called nettleleaf noseburn, is a species of flowering plant in the spurge family (Euphorbiaceae). It is native eastern to North America, where it is found in the southeastern United States. Its typical natural habitat is in rocky or sandy dry woodlands, over calcareous or mafic substrates. Tragia urticifolia is an erect perennial herb or subshrub.
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The South Patagonian Batholith () is group of plutons in southwestern Patagonia. The rocks of batholith include granite, leucogranite, tonalite, granodiorite, diorite, gabbro and mafic dykes. The earliest plutons of the batholith formed in the Late Jurassic with the magmas likely being derived from anatexis. This early magmatism produced a bimodal magmatism that formed both leucogranite and gabbro.
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The BGB consists of locally derived sediments and chemical sediments, but is composed mostly of TTGs and greenstones, as briefly discussed above. Three main lithostratigraphic units are used to divide the BGB. The base contains the Onverwacht, followed by the Fig Tree, and the topmost Moodies Groups. The Onverwacht Group is composed largely of mafic and ultramafic volcanics.
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The Tuzgle volcano proper is constructed from an older rhyodacite-mafic series and a more recent series constructed from andesites alone. These and neighbouring shoshonitic centres are formed from magmas with crustal contamination. Isotope analysis of magmatic rocks have shown La/Nb ratios of 1.31.6 and Ba/Ta ratios of 160260, lower than in the main volcanic front.
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The magmas from the spreading ridge and the hotspot have differences. For one, they contain dissimilar concentrations of elements like Na2O, CaO and Sr at a given mafic level. This difference highlights that the magmas were formed at different depths in the mantle. It is theorized that the hotspot magma was melted deeper than that of the ridge.
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Small protocontinents (cratons) formed as crustal rock was melted and remelted by hot spots and recycled in subduction zones. There were no large continents in the early Archean, and small protocontinents were probably the norm in the Mesoarchean because they were prevented from coalescing into larger units by the high rate of geologic activity. These felsic protocontinents (cratons) probably formed at hot spots from a variety of sources: mafic magma melting more felsic rocks, partial melting of mafic rock, and from the metamorphic alteration of felsic sedimentary rocks. Although the first continents formed during the Archean, rock of this age makes up only 7% of the world's current cratons; even allowing for erosion and destruction of past formations, evidence suggests that only 5 to 40 percent of the present continental crust formed during the Archean.
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The ophiolites of the Zermatt-Saas zone are mostly ultramafic rocks with greenschist facies mineralogy: serpentinites. Some mafic parts exist, they also have greenschist assemblages of actinolite, plagioclase and sometimes epidote or clinozoisite. However, relicts are found of blueschist and eclogite facies metamorphism during the Eocene, which shows that the current greenschist assemblage of the Zermatt-Saas zone is a retrograde overprint.
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The volcanic complex has been affected by faulting. Ignimbrites erupted at La Hoyada have been described as moderately welded andesites, of green-grey colour. The intermediate composition of dykes at La Hoyada contrasts with that of other volcanic rocks associated with extensional tectonics in the Puna, which tend to be of mafic composition. Some of the rocks underwent supergene mineralization later.
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One series of ignimbrites surrounding Taftan which reaches thicknesses of and reaches distances of from the edifice may be 2 million years old. The basement of Taftan is formed by various sedimentary rocks, along with some mafic volcanic rocks and metamorphic rocks. At Taftan, the Nehbandan-Khash flysch borders the Makran zone. The oldest rocks are limestones from the Cretaceous period.
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The basement consists mainly of Precambrian-Paleozoic metamorphic rocks with intruded granitic, mafic and ultramafic rocks of Paleozoic age; these metamorphic rocks are also known as the Puncoviscana Formation. There are Paleogene-Neogene continental sequences. It is mostly buried beneath Quaternary sediments; outcrops have characteristic dark colours. The Quaternary sediments in turn contain both aeolian, colluvium and alluvium-derived sediments.
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Temperatures of the magma chamber range from ; the mafic magmas that are injected in the chamber are about hotter than the extant andesite and dacite. The chamber may be surrounded by skarnic alteration. This alteration gives rise to wollastonite and pyroxene-containing skarn, depending on the distance from the magma chamber walls. Metasomatism does further affect rocks derived from magma chamber walls.
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Mafic dikes up to 20 feet in width occur throughout the area. Glacial advances occurred 7,000, 5,000 and 500 years ago, with the last extending to the entrance of the bay, where it left a huge semicircular terminal moraine. The consequent surface glacial deposits include gravels as outwash and moraines. Glacial gravels extend up to 2000 feet up the mountain slopes.
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Ophiolite series and ultramafic rocks have a widespread occurrence in Iran and can be grouped as follows: Ultramafic and mafic units of Late Precambrian–Early Cambrian. Although comparable to modern ophiolites, these rocks do not display all typical features of an oceanic crust. The term “old ophiolite” might be a misnomer. These rocks are widespread in Takab and Anarak Regions.
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Stony Creek flows from the Piedmont to the Coastal Plain of Virginia. The forming confluence is at the edge of mafic and felsic rocks metavolcanic rocks and the Petersburg Granite. Petersburg Granite underlies most of the course and once in the Coastal Plain, it flows a short distance through the Windsor Formation and then through alluvium to the Nottoway River.
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Tebenquicho is a volcano in Argentina. The volcano is constructed by lava domes, lava flows and pyroclastic flows. Among its eruption products are potassium-rich dacites which show evidence of having interacted with the crust when they formed. The volcano was active between 14 and 6 million years ago; as volcanism waned mafic activity started up elsewhere in the Puna.
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A lava dome cluster is recognizable in the central sector of the volcano, forming a flat area with a surface of . The volcano contains basaltic rocks with an extrusion formed from more silicic rock. Layers of mafic andesite, scoria and some pumice extend outwards away from the central sector. The volcano rises above its terrain and its average summit slope is 26°.
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Both are intruded by granites associated with the Iwokrama Formation. Some folding occurred before these were overlain by the locally unconformable almost flat lying Roraima GroupGibbs, A.K & Barron, C.N (1993). The Geology of the Guiana Shield. Oxford University Press.. Major mafic sills and dykes of the Avanavero Suite intrude all of the older rocks, and are part of a Large Igneous Province (LIP).
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This comprises up to seven thick columnar cooling units of alkali basalt separated by buff-weathered vesicular lava flows. Renewed volcanism sent a series of massive ankaramite lava flows over the second unit and have a total thickness of . These lava flows, comprising the third unit, are spheroidally weathered. The mafic shield-building stage culminated with emplacement of the fourth and highest unit.
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The Slide Mountain Terrane is a late Paleozoic terrane made of a complex of oceanic rocks in northern and southern British Columbia, Canada. The rocks of the terrane include Carboniferous limestones, fine grained quartz rich clastics, conglomerates and volcanic rocks. Permian Kalso Group mafic volcanics are included. The Kalso Group volcanics originated from an ocean ridge environment adjacent to the Permian continental margin.
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The dense oceanic plate has a high tendency to sink. As it sinks, it breaks along the oceanic plate and the welded crust above and a gap is created. The extra space created leads to the decompression melting of mantle wedge materials. The melts flow upward and fill the gap and intrude the oceanic plate and welded crust as mafic dykes intrusion.
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Lizard and the Meneage. (Memoir 359). British Geological Survey that summarised thinking up to the point of publication, proposed that the serpentinite body represented an intruded mass of ultra-mafic material. They believed that the foliations were the result of mass flux within the cooling magma body, and that the different types of serpentinite were the result of an igneous cooling alteration rim.
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In geology, a melanosome is a dark,Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks, Part 6. Migmatites and related rocks, p2. mafic mineral band formed in migmatite which is melting into a eutaxitic texture ; often, this leads to the formation of granite. The melanosomes form bands with leucosomes, and in that context may be described as schlieren or migmatitic.
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Water has limited solubility in silicate melts ranging from almost 0% at surface pressure to 10% at 1100 °C and 5 kbar of pressure for a granitic melt.Hall, Anthony, Igneous Petrology, Longman, 1987, pp. 253-260 Solubility is lower for more mafic magmas. As the temperature and pressure drop during emplacement and cooling of the magma a separate aqueous phase will exsolve.
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Hercynite is a spinel mineral with the formula FeAl2O4. It occurs in high- grade metamorphosed iron rich argillaceous sediments as well as in mafic and ultramafic igneous rocks. Due to its hardness it also is found in placers. It was first described in 1847 and its name originates from the Latin name for the Harz, Silva Hercynia, where the species was first found.
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TTGs are an aggregation of certain rocks (tonalite-trondhjemite- granodiorite), that form when hydrous, mafic crust is melted at high pressure. These rocks are critical to the formation of Archean greenstone complexes due to the low density, intrusive nature of the rocks. TTGs are found in other Archean greenstone belts such as Isua and Barberton. The processes that form TTGs are debated.
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In the northern group these are primarily composed from feldspar with minor components of amphibole, biotite and quartz. The southern group rocks have similar petrologies, but are of rhyolitic composition and contain mafic components. They contain a rhyolitic core surrounded with andesitic lavas that contains primarily plagioclase phenocrysts. Temperatures of for dacitic lava and for rhyolite lava have been estimated.
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Changes in subduction style of the Nazca plate have produced changes in the nature and amount of volcanic activity, with the latest change being a westward shift of volcanic activity to the main belt of the Central Volcanic Zone. In the region, mafic volcanism has been active since the Oligocene. Most volcanism in the area is of silicic nature however.
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Panicum flexile, commonly called wiry panicgrass, is a species of flowering plant in the grass family (Poaceae). It is primarily native to eastern to North America, where it has a scattered and localized distribution. It is typically found in mafic or calcareous open areas, both wet and dry, particularly associated with limestone. Panicum flexile is a rather delicate annual grass.
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This material is found in Chaac Patera and thought to mimic the Kilauea Caldera floor overall, which would form from low viscosity, dark lavas ranging from mafic to ultramafic composition. Hummocks or pits are thought to be from the effect of inflation or vent openings that are common in this type of lava flow. Dark colored materials are the source of more heat.
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The Cienago ignimbrite is a highly evolved magma. Magmas from the Panizos ignimbrite display only weak variations that may be linked to temperature differences in the magma chamber. The magmas of the Panizos ignimbrite underwent strong crystallization between eruptions and crystals are often heavily modified. The formation of all magmas was initiated by the interaction of mafic mantle melts with the crust.
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However, beryllium and chromium do not tend to occur in the same types of rock. Chromium is most common in mafic and ultramafic rocks in which beryllium is extremely rare. Beryllium becomes concentrated in felsic pegmatites in which chromium is almost absent. Therefore, the only situation where an alexandrite can grow is when Be-rich pegmatitic fluids react with Cr-rich country rock.
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There is an unconformity where the Karoo rocks of the basin overlie much older rocks. The southern flank of the basin is underlain by Waterberg Group rocks, which form between two-thirds and three-fourths of the basin floor. Mafic rocks of the Limpopo Belt underlie the basin floor in the northeast. The Bushveld Complex underlies the basin in the southeast.
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Some sources also identify the overlying Wellington Formation, predominantly a mudstone, as a Dwyka Group equivalent. The Ecca Group, the second of the four groups in the Karoo Supergroup, is represented by the Wellington (alternatively assigned to the Dwyka Group), Swartrant (Vryheid Formation equivalent), and Grooteguluk Formations. The Swartrant Formation is predominantly mudstone derived from a mafic source. It includes some coal.
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Map of the Matachewan and Mistassini dike swarms of Eastern Canada The Mistassini dike swarm is a 2.5 billion year old Paleoproterozoic dike swarm of western Quebec, Canada. It consists of mafic dikes that were intruded in the Superior craton of the Canadian Shield. With an area of , the Mistassini dike swarm stands as a large igneous province.Igneous rock associations in Canada 3.
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The rocks in the watershed date to the Precambrian Era and Lower Paleozoic Era. The surficial geology mainly consist of felsic gneiss and mafic gneiss formations, with small amounts of serpentinite near the mouth of the creek. Two soil associations exist in the Little Darby Creek watershed. The Neshaminy-Lehigh-Glenlg soil association is prevalent in much of the watershed.
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Harlan, Stephen S.; Geissman, John W.; Snee, Lawrence W.; and Reynolds, Richard L. "Late Cretaceous Remagnetization of Proterozoic Mafic Dikes, Southern Highland Mountains, Southwestern Montana: A Paleomagnetic and 40Ar/39Ar Study." Geological Society of America Bulletin. 108:6 (June 1996). igneous rocks about 40 miles long and 20 miles wide (800 square miles, or 2,071 square kilometers)Merrill-Maker, Andrea.
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They are very viscous (thick and sticky) and rich in dissolved gases. Mafic magmas, on the other hand, are low in volatiles and commonly erupt effusively as basaltic lava flows. However, these are only generalizations. For example, magma that comes into sudden contact with groundwater or surface water may erupt violently in steam explosions called hydromagmatic (phreatomagmatic or phreatic) eruptions.
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Planet Mars – volatile gases (Curiosity rover, October 2012) The most common form of volcanism on the Earth is basaltic. Basalts are extrusive igneous rocks derived from the partial melting of the upper mantle. They are rich in iron and magnesium (mafic) minerals and commonly dark gray in color. The principal type of volcanism on Mars is almost certainly basaltic too.
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Baddeleyite belongs to the oxide group, having a composition of ZrO2. Similar minerals belonging to the same group are the rutile group: rutile (TiO2), pyrolusite (MnO2), cassiterite (SnO2), uraninite (UO2) and thorianite (ThO2). Baddeleyite is chemically homogeneous, but it may contain impurities such as Ti, Hf, and Fe. Higher concentrations of Ti and Fe are restricted to mafic-ultramafic rocks.
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Aerinite from Spain Aerinite (Ca4(Al,Fe,Mg)10Si12O35(OH)12CO3·12H2O) is a bluish-purple inosilicate mineral. It crystallizes in the monoclinic system and occurs as fibrous masses and coatings. It has a dark, vitreous luster, a specific gravity of 2.48 and a Mohs hardness of 3. It is a low-temperature hydrothermal phase occurring in zeolite facies alteration of mafic rocks.
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The ophiolites are found in serpentinized ultra-mafic masses or sometimes as more complete ophiolite complexes. Apart from ultrabasic rocks, there is also diabase, gabbro, peridotite and basalt. In the Vardar Zone, a series of faults and diapirs are laminated and highly serpentinized. The Radusha Massif is the most significant ophiolite massif, covering an area of 60 square kilometers northwest of Skopje.
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Coyoteite is a hydrated sodium iron sulfide mineral. The mineral was named coyoteite after Coyote Peak near Orick, California where it was discovered (along with another rare mineral, orickite). This mineral is unstable under normal atmospheric conditions, making it rare at the surface. The mineral was first described in a petrographic study of a sample of a mafic diatreme at Coyote Peak.
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These characteristics are similar to N-MORB mantle sources with low pressure crustal contamination. The eastern subprovince is composed of mafic rocks that are mildly enriched in incompatible elements. The highest concentrations of incompatible elements are found in tholeiites of the Mahajanga basin, the Tampokesta Kamoreen area and the Tamatave area. 144Nd/143Nd ratios also have a narrower initial range.
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The Punta de Choros Metamorphic Complex is a large coherent group of metamorphic rocks –in other words a geologic complex– of the Chilean Coast Range in northern Chile. It consists mainly of micaschists, greenschists and other low-grade metasediment. The complex was formed by the metamorphism of sediments and associated mafic rocks at the interface between a subducting plate and the overriding plate.
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These belts are associated with sedimentary rocks that occur within Archean and Proterozoic cratons between granitic bodies. Their name is derived from the green hue that comes from the metamorphic minerals associated with the mafic rocks. These regions are theorized to have formed at ancient oceanic spreading centers and island arcs. In simple terms, greenstone belts are described as metamorphosed volcanic belts.
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Closure of the Manikewan Ocean is believed to have begun by 1915 million years ago, though the first evidence of this ocean closure along the western Superior margin is the initiation of magmatism in the 1890 million year old Snow Lake Arc, interpreted as a subduction zone that formed outboard (towards the ocean) from the Superior Boundary Zone. Mafic to ultramafic magmatism in the Winnipegosis Komatiite Belt is contemporaneous with ongoing magmatism in the Snow Lake Arc, which implies the Winnipegosis Komatiite Belt formed along a convergent plate boundary. The Winnipegosis Komatiite Belt forms part of the ~3000 km Circum-Superior Belt, considered a mantle plume-derived large igneous province. The Winnipegosis Komatiite Belt itself predominantly consists of tholeiitic basalt and komatiite, intercalated with lesser amounts of carbonate and shale sediments, and intruded by mafic and ultramafic cumulates.
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Kilimafedha greenstone, Orangi River, Serengeti NP Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies. The name comes from the green hue imparted by the colour of the metamorphic minerals within the mafic rocks: the typical green minerals are chlorite, actinolite, and other green amphiboles. A greenstone belt is typically several dozens to several thousand kilometres long and although composed of a great variety of individual rock units, is considered a 'stratigraphic grouping' in its own right, at least on continental scales. Typically, a greenstone belt within the greater volume of otherwise homogeneous granite-gneiss within a craton contains a significantly larger degree of heterogeneity and complications and forms a tectonic marker far more distinct than the much more voluminous and homogeneous granites.
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A series of eruptions built up a broad plateau of lava, and extended over the area where Calabozos now lies. Locally, this plateau was composed of mafic andesite with olivine, which over time gathered to form to thick layers. Nearby volcanoes sit on top of two mya lavas that formed during this period, while the Loma Seca Tuff lies atop andesitic deposits from Descabezado Grande.
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The source for the Mackenzie dike swarm is considered to have been a mantle plume center called the Mackenzie hotspot. About 1,268 million years ago, the Slave craton was partly uplifted and intruded by the giant Mackenzie dike swarm. This was the last major event to affect the core of the Slave craton, although later on some younger mafic magmatism registered along its edges.
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Cerro Morado is a monogenetic volcanic field, in Argentina. It is part of a group of mafic volcanic centres in the Altiplano-Puna region, which is dominated by silicic rocks such as dacitic - rhyolitic rocks. The field was formed during eruptions 6.4 million years ago which probably lasted from half a year to several years. These eruptions formed scoria cones and a plateau of lava flows.
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The amount of magma generated is small, most of it is primitive mafic magma, and its ascent was controlled by local tectonic structures. In the case of Pasto Ventura, the composition of the magmas is influenced by fluids emanating from the downgoing Nazca Plate slab as well as by a relic mantle that already influenced magma composition during the Famatinian Orogeny 485 million years ago.
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The iron formations are composed of alternate layers of magnetite, white quartzite, jasper, grey cherty quartz, and/or tremolite- chlorite tuff. They are intruded by sills composed of medium-grained, white- weathering, quartz diorite that range in thickness from to . These rocks are similar to the coarse thicker parts of lava flows, but are interpreted to be partly intrusive, likely conduits that produced mafic volcanism.
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Mesozoic rocks from 251 to 66 million years ago are largely absent in Guinea-Bissau. In the west, there is an unconformity between Paleozoic sediments and Cenozoic marine sediments, which are cut by mafic dykes. In the past 2.5 million years of the Quaternary, Guinea-Bissau's surficial geology and geomorphology have changed considerably, with the formation of new terraces and duricrust, as well as frequent marine transgressions.
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Mount McKay is a mafic sill located south of Thunder Bay, Ontario on the Indian Reserve of the Fort William First Nation. It formed during a period of magmatic activity associated with the large Midcontinent Rift system about 1,100 million years ago. McKay was originally known as the "Thunder Mountain" (Animkii Wajiw) in the Ojibwe language. The mountain is used by the Ojibwe for sacred ceremonies.
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Geologic column for the park region (click image to enlarge) The Cadillac Mountain Intrusive Complex is part of the Coastal Maine Magmatic Province, consisting of over a hundred mafic and felsic plutons associated with the Acadian Orogeny. Mount Desert Island bedrock consists mainly of Cadillac Mountain granite. Perthite gives the granite its pinkish color. The Silurian age granite ranges from 424 to 419 million years ago (Mya).
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In the Neoproterozoic, Ghana was affected by the Pan-African orogeny. Today, the Pan-African mobile belt terrane spans eastern and southeastern Ghana, with several different units. The Dahomeyan System comprises both mafic and felsic gneiss while the Togo Series includes quartzite, shale and small amounts of serpentinite. The Buem Group is a mix of sediments and igneous rocks, including shale, sandstone, basalt, trachyte and volcanoclastic rocks.
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Madeira began to form more than 100 million years ago in the Early Cretaceous, although most of the island has formed in the last 66 million years of the Cenozoic, particularly in the Miocene and Pliocene. The island is an example of hotspot volcanism, with mainly mafic volcanic and igneous rocks, together with smaller deposits of limestone, lignite and other sediments that record its long-running uplift.
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They might be representing a protorift. Ultramafic and mafic rocks of Upper Paleozoic occur as metamorphosed as well as non-metamorphosed bodies in some areas like Fariman, Shanderman, and Asalem. These rocks display many typical features of modern ophiolites. Ophiolite series of Early Cretaceous–Paleogene age show typical features of ophiolitic sequences and are thought to be associated with the closure of the Neotethys.
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In the late Miocene, more evolved andesite magmas were erupted and the crustal components increased. In the late Tertiary until the Quaternary, a sudden decrease of mafic volcanism coupled with a sudden appearance of rhyodacitic and dacitic ignimbrites occurred. During this flare-up it erupted primarily dacites with subordinate amounts of rhyolites and andesites. The area was uplifted during the flare-up and the crust thickened to .
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Other active centres include the El Tatio and Sol de Mañana geothermal fields and the fields within Cerro Guacha and Pastos Grandes calderas. The latter also contains <10 ka rhyolitic flows and domes. The implications of recent lava domes for future activity in the APVC are controversial, but the presence of mafic components in recently erupted volcanic rocks may indicate that the magma system is being recharged.
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The magmas are mixtures of crust derived and mafic mantle- derived melts with a consistent petrological and chemical signature. The melt generation process may involve several different layers in the crust. Another model requires the intrusion of basaltic melts into an amphibole crust, resulting in the formation of hybrid magmas. Partial melting of the crust and of hydrous basalt generates andesitic–dacitic melts that escape upwards.
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Diamond Head, a tuff cone Most of the moais in Easter Island are carved out of tholeiite basalt tuff. Mafic volcanism typically takes the form of Hawaiian eruptions that are nonexplosive and produce little ash. However, interaction between basaltic magma and groundwater or sea water results in hydromagmatic explosions that produce abundant ash. These deposit ash cones that subsequently can become cemented into tuff cones.
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Characteristically the granites and similar rocks of the Transscandinavian Igneous Belt are rich in alkali elements (e.g. sodium and potassium) and have porphyritic textures. Not all rocks of the Transcandinavian Igneous Belt have a pure alkaline character, some display chemistries tending to the calc- alkaline magma series. In addition to the above-mentioned rocks lesser amounts of mafic intrusives are also part of the belt.
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The watershed formed by the Banner Mountain has many geological formations. The rock types recorded are mafic rocks such as gabbro, serpentine rocks, an ultramafic rocks and granitic rocks consisting of quartz monzonite, and metavolcanic rocks. Consequently, the soil formations of the watershed exhibit soil types derived from gabbro and serpentine. These soils do not permit growth of most plants due to their chemical properties.
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Level Mountain has experienced volcanic eruptions sporadically for the last 15 million years, making it the most persistent volcano of the NCVP. More than 20 eruptive centres are present on the summit and flanks of the complex. These have produced mainly felsic and mafic lavas, a chemical composition range typical of bimodal volcanism. Such volcanism commonly occurs at hotspots, continental rifts and leaky transform faults.
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TIB granitoids dominate the Eastern segment north of Lake Vattern. In the Western segment, metavolcanic rocks and metagraywacke from 1.76 billion years ago is most common. The Amal-Horred belt contains younger intermediate metavolcanic rocks, intruded by calc-alkaline granitoids. Granite, syenite and mafic intrusions are distributed throughout the broader grouping of Sveconorwegian rocks, which intruded before the Gothian event, but before extensive deformation took place.
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Ollagüe has erupted rocks ranging from basaltic andesite to dacite. Blobs of basaltic andesite are found in all rocks from the volcano; they probably formed when mafic magma was quenched by colder felsic magma. The andesites and dacites are relatively rich in crystals. Phenocrysts in the main andesite-dacite series include amphibole, apatite, biotite, clinopyroxene, ilmenite, magnetite, orthopyroxene, plagioclase and rarely olivine, quartz and zircon.
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Partial melting of mantle generate mafic dykes intrusion. Because the mantle is the primary source, these dykes record isotopic characteristics of the depleted mantle in which the 87Sr/86Sr ratio is near 0.703 and εNd is positive. On the other hand, partial melting of the lower crust (accretionary complex) leads to S-type granitoids intrusion with enriched aluminum oxide throughout the evolution of divergent double subduction.
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These conditions were common in some layered mafic intrusions, most of which are Proterozoic in age, which formed from enormous sill-like intrusions of basalt into lower continental crust. The classic example of a Proterozoic layered intrusion with cumulate harzburgite is the Stillwater igneous complex of Montana, U.S.A. It is also found in the Bushveld Igneous Complex, a large layered intrusion in South Africa.
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To the south near Lake Superior, rock strata of the Duluth and Beaver Bay complexes are interspersed with and underlie the extrusive rock of the North Shore Volcanic Group.Ojakangas & Matsch (1982), pp. 52, 56. The Beaver Bay Complex occupies the center of the North Shore Volcanics, and is slightly younger in age than the other mafic rocks of the Duluth Complex, dating from c.
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The term "sanukitoid suite" includes more evolved rocks derived from sanukitoid through fractional crystallization. Sanukitoids are similar in major and trace element composition to "adakites" (named for occurrences on the Adak Island in the Aleutian island arc). Both suites are thought to form by melting of a mafic igneous rock protolith that has been metamorphosed to garnet-pyroxene (eclogite) or garnet-amphibole assemblages (Rapp et al.
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Diorite has a phaneritic, often speckled, texture of coarse grain size and is occasionally porphyritic. Orbicular diorite shows alternating concentric growth bands of plagioclase and amphibole surrounding a nucleus, within a diorite porphyry matrix. Diorites may be associated with either granite or gabbro intrusions, into which they may subtly merge. Diorite results from the partial melting of a mafic rock above a subduction zone.
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The Nipigon diabase sills give evidence of rift-related continental basaltic magmatism during the Midcontinent Rift System event, estimated at 1,109 Ma ago. Thick sills up to thick are also related with the rifting event, forming cliffs that are up to high. The mafic and ultramafic intrusions centered on Lake Nipigon is interpreted to represent a failed arm of the Nipigon embayment.Sutcliffe, R.H., 1991.
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A self-employed chemical analyst, Sahlbom was contracted by mineralogists and petrographers for her proficient work. In 1916 she published a second report on mineralogy and radioactivity, with 400 springs and wells analyzed. The paper confirmed that the radioactivity of mineral waters was related to geology. Overall, acid and primary rocks resulted in the most radioactive emanation; mafic and sedimentary rocks demonstrated less radioactivity.
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The footwall to the Widgiemooltha Komatiite is the Mt Edwards Basalt, which is a low to medium MgO mafic extrusive rock, metamorphosed to upper greenschist facies. Mineralogy is chlorite, actinolite, rare epidote, quartz and albite. The Mt Edwards Basalt has uncommon interflow sedimentary intervals and some well developed pillow basalt flow tops which give regional facing directions. The true thickness of the Mt Edwards Basalt is unknown.
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Mafic volcanic rocks overlie quartzite in the Powder Mill Group and Bessemer, which begin northeast of Hayward, Wisconsin and extend northeast, meeting the string of intrusive complexes. From as far south as Polk County northeast through Burnette, Washburn, Bayfield and much of Douglas counties are the widespread basalt flows of the Chengwatana Volcanic Group in the west and the Portage Lake Volcanics in the east.
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Ophiolites are sequences of mafic to ultramafic rock generally believed to represent ancient oceanic lithosphere. They are distributed all across the world being all of them located at present or past orogenic belts, sites of mountain building processes. Ophiolites are common in orogenic belts of Mesozoic age, like those formed by the closure of the Tethys Ocean. Ophiolites in Archean and Paleoproterozoic domains are rare.
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There is an alternate idea that early Earth plate tectonics began by vertical movement of the lithosphere, rather than the modern horizontal tectonics. This theory rejects the idea of subduction and arc accretion in the formation of greenstone belts. It suggests that convective overturn due to density differences between the overlying mafic sequence (greenstone) and partially molten granitic middle crust is responsible for the observed formations.
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The Intercaldera Sequence is divided into, in ascending order, the Scoullar Mountain formation, Little Mount Pleasant formation, Seelys formation, and McDougall Brook Granite formation. In addition, there are felsic dykes and one mafic dyke that intrude the Scoullar Mountain and Little Mount Pleasant formations, respectively. The first sequence in the order is the Scoullar Mountain formation. The layer is characterized by sedimentary breccia and interbedded andesitic lava.
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Mount Asahi is an active stratovolcano, in height that arose southwest of the Ohachi-Daira caldera. The Japan Meteorological Agency gave the region rank C in volcanic activity. The volcano consists mainly of andesite and dacite, Holocene volcanic non-alkali mafic rock less than 18,000 years old. In addition to the main peak, there is a smaller volcano emerging from the southeast shoulder of the mountain, .
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The material excavated to form Montes Rook came from a mafic layer below an anorthositic zone. Many of the peaks in this ring are composed of pure anorthosite. Sections of the gap between these sub-ranges contain long valleys filled in places with basaltic lava, forming small lunar maria. One such section along the northeastern part of the range has been named Lacus Veris.
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Chela is a volcano in Chile that was active between 3.75±0.5 and 4.11±0.25 million years ago. It is constructed on top of the 5.4±0.3 million years old rhyolitic Carcote ignimbrite. Its eruption products are mafic andesites. The volcano was degraded by glaciation but radial ridges and red-gray rocks as well as the uniform slopes indicate that it was a symmetric stratovolcano.
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It is estimated that Bajo de la Alumbrera contains of copper. The mineralization may have originated in mafic magmas. The formation process of these deposits is insofar different from that of other Andean porphyry deposits as it was formed by several hydrothermal systems that were separated only by a few million years, while e.g. the copper porphyry El Salvador formed during episodic magmatic activity.
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The geology of the Norwegian Sea began to form 60 million years ago in the early Cenozoic, as rifting led to the eruption of mafic oceanic crust, separating Scandinavia and Greenland. Together with the North Sea the Norwegian Sea has become highly researched since the 1960s with the discovery of oil and natural gas in thick offshore sediments on top of the Norwegian continental shelf.
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The main components of the rocks at La Breña-El Jagüey are clinopyroxene, ilmenite, olivine, plagioclase and titanomagnetite, with rocks sporting variable textures. The participation of water in the formation process of these magmas is debatable; the rocks may have been influenced by sediments from the uppermost part of the subducting Farallon slab. These rocks are of mafic intraplate geochemistry. The rocks contain mantle xenoliths.
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The bright areas are now known to be locations where fine dust covers the surface. The dark markings represent areas that the wind has swept clean of dust, leaving behind a lag of dark, rocky material. The dark color is consistent with the presence of mafic rocks, such as basalt. The albedo of a surface usually varies with the wavelength of light hitting it.
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It prefers mafic (siliceous) rock substrates. In Joshua Tree National Park is can be seen on vertical granite and gneiss faces in washes.Photo Gallery, Joshua Tree Lichens, Joshua Tree National Park website, National Park Service, It is common worldwide in the Northern Hemisphere. It is very common in the Sonoran Desert from southern California to Arizona, Baja California, and Sonora, Chihuahua, and Sinaloa, Mexico.
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The Caopacho in turn flows south to join the Moisie River. Parts of the east and south of the reserve drain into the watershed of the Nipissis River, another tributary of the Moisie River. The reserve is in the Grenville geologic province, with basement rocks consisting mainly of metamorphic gneiss and paragneiss. There is some mafic bedrock in north of the reserve, including diorite and gabbro.
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John Wiley & Sons, 1997 The mineral occurs within cavities in nepheline syenites, carbonatites, in hydrothermal veins and various mafic rocks. It occurs associated with thomsonite, analcime, natrolite, harmotome, brewsterite, prehnite and calcite. The mineral was first reported by and named for Scottish mineral collector James Edington (1787–1844).Handbook of Mineralogy Other sources (including the mineralogist Haidinger) credit Scottish geologist and mineralogist Thomas Edington (1814-1859).
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The Groulx Mountains are part of the Grenville Province, a geological division of the Canadian Shield. They are composed of Precambrian rocks that have been deformed during the Labrador and Grenville orogenies. The massif is composed mostly of gabbro-norite, a mafic rock rich in magnesium and iron. The northern part of the massif is mostly composed of anorthosite and the east of gneiss and paragneiss.
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Essexite can be considered as an alkali gabbro or monzodiorite primarily composed of nepheline, plagioclase, with lesser amounts of alkali feldspar, with mafic minerals composed of any of the following; titanium augite (pyroxene), hornblende and biotite. Trace mineralogy may include magnetite, ilmenite and accessory olivine (<5%). Essexite grades into a nepheline monzogabbro with a decrease in potassium feldspar and an increase in the feldspathoid minerals.
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There are a number of subfeatures including the Inaccessible Cones, Little Belknap, South Belknap, and Twin Craters, as well as the Belknap hot springs. Postglacial, mafic eruptions are more common in the Sisters Reach — which includes Belknap — than anywhere in the Cascade volcanic arc. However, the Volcano Hazards Program of the United States Geological Survey considers it unlikely that Belknap will erupt again soon.
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"Mineralogy at Meridiani Planum from the Mini-TES Experiment on the Opportunity Rover". Science: 306. 1733–1739 Using results from the chemical measurements, mineral models suggest that the soil could be a mixture of about 80% iron-rich clay, about 10% magnesium sulfate (kieserite?), about 5% carbonate (calcite), and about 5% iron oxides (hematite, magnetite, goethite?). These minerals are typical weathering products of mafic igneous rocks.
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About 1575–1562 Ma ago the Progine Zone was intruded by mafic magma during the same time spans as Rapakivi granites intruded more easterly domains in Fennoscandia. Later 1224–1215 and ca. 1204 Ma ago the progine zone was subject to extensional tectonics perhaps being a back-arc basin. The Protogine Zone obtained its final configuration during the Sveconorwegian orogeny 1130–950 Ma ago.
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Channelization and rebuilding a culvert carrying the stream under Main Street have been proposed as flood control measures. The Hardyston Formation and felsic to mafic gneiss is present in the watershed of Polk Valley Run. The stream's valley is also home to some quartzite that is slightly atypical for the region: brittle and gray with pebbles up to three eighths of an inch in diameter.
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On a large scale, it is composed of Kinney Lakes granodiorite and the younger Topaz Lake granodiorite. On a finer scale, the Intrusive Suite of Sonora Pass is made of light-gray, coarse-grained biotite granodiorite, plus granite with roughly equant, well-formed potassium feldspar phenocrysts composing about 2–10% of the rock. Quartz usually occurs in clots of . The mafic mineral content is about 10%.
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Azurite-Chrysocolla-Malachite specimen from Whim Creek. 5.0 x 4.0 x 2.9 cm. The Whim Creek Copper Mine extracts two volcanogenic massive sulfide ore deposits, namely Mons Cupri (lit. copper mountain) and Whim Creek, which are located within the Cistern Formation and Rushalls Slate sedimentary members, which are part of a series of rift-related felsic, intermediate and mafic volcanic rocks known as the Whim Creek Group.
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Sedimentary and volcanic rocks crop out on the eastern shores of the Lake Ladoga in Russia. Among these are the "Salmi series" or "Salma suite" and the "Priosersk suite", which are Jotnian units. These rocks overlie the Salma rapakivi granite and igneous and metamorphic rocks of Paleoproterozoic age. Gritstone, sandstone and conglomerate are the sedimentary components of the Salmi suite which further includes mafic volcanic rocks.
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Tachylite from Kīlauea volcano in Hawaii (view is about 9 cm across) Tachylite (also spelled tachylyte) is a form of basaltic volcanic glass. This glass is formed naturally by the rapid cooling of molten basalt. It is a type of mafic igneous rock that is decomposable by acids and readily fusible. The color is a black or dark-brown, and it has a greasy-looking, resinous luster.
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It occurs as a secondary mineral in mafic igneous rocks often filling vesicles along with zeolites in basalt. Unlike most localities throughout the world, the occurrence of datolite in the Lake Superior region is usually fine grained in texture and possesses colored banding. Much of the coloration is due to the inclusion of copper or associated minerals in progressive stages of hydrothermal precipitation. Botryolite is a botryoidal form of datolite.
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Calabozos lies between two different types of volcanism—to its north, andesite and rhyolite are the primary constituents of lava while its southern neighbors are composed of more mafic andesite and basalt. It is mainly basaltic andesite and rhyodacite that make up Calabozos, forming a calcalkilic suite rich with potassium. Its lavas are dotted with phenocrysts, which vary from 2 to 25 percent of their mass.Grunder and Mahood (1988), p. 831.
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The granitic magma mixed both I- and S-type of granitoids; these two different magmatic compositions imply that there are different sources of magma, including new magma from mantle plume and partial melting of pre- existing crust. In TTG, there are tonalities and tondhjemite. However, tonalities and trondhjemites are different; they are mainly composed of mafic and felsic minerals respectively. They were formed by partial melting of pre- existing crust.
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The formation also has local occurrences of pyroxenite and hornblendite. Further east, the recumbent folds of the Marampa Group overly granites and may contact the Rokel River Group at a fault. The Marampa Group formed 2.1 billion years ago, in the early Proterozoic and deformed 560 million years ago at the beginning of the Pan-African orogeny. The group includes ironstone, volcanic sediments and both mafic and felsic volcanic rocks.
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The Southern Cross Province lies in the central area of the Yilgarn craton. The Marda–Diemals greenstone belt in the Southern Cross Terrane can be divided into three layers: the lower greenstone belt (ca. 3.0 Ga) characterized by mafic volcanic rock and banded iron formation, a felsic-intermediate volcanism layer, and an upper sedimentary layer (ca. 2.73 Ga) of calc-alkaline volcanic (Marda Complex) and clastic sedimentary rocks (Diemals Formation).
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Soapstone Ridge is a mafic-ultramafic geological complex located in the Piedmont region, south-east of Atlanta, Georgia on a area in DeKalb County and neighboring Fulton and Clayton Counties. The ridge was named from its deposits of metapyroxenite, which early settlers wrongly believed was soapstone. Many archaeological sites, including Late Archaic quarry sites dated between 600 BCE and 1500 BCE, occur on Soapstone Ridge.Freeman, David B.(1997).
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Roughly three-quarters of all Martian meteorites can be classified as shergottites. They are named after the Shergotty meteorite, which fell at Sherghati, India in 1865.Shergotty Meteorite - JPL, NASA Shergottites are igneous rocks of mafic to ultramafic lithology. They fall into three main groups, the basaltic, olivine-phyric (such as the Tissint group found in Morocco in 2011) and lherzolitic shergottites, based on their crystal size and mineral content.
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The main host minerals for nickel and cobalt can be either iron oxides, clay minerals or manganese oxides. Iron oxides are derived from mafic igneous rocks and other iron-rich rocks; bauxites are derived from granitic igneous rock and other iron-poor rocks. Nickel laterites occur in zones of the earth which experienced prolonged tropical weathering of ultramafic rocks containing the ferro-magnesian minerals olivine, pyroxene, and amphibole.
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In geology, felsic is an adjective describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, Essentials of Geology, W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium.
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Journal of the Geological Society of London, 141, 501-510. and mafic sub-volcanicGraham, J.R., Russell, K.J. & Stillman, C.J. (1995) Late Devonian magmatism in west Kerry and its relationship to the development of the Munster Basin. Irish Journal of Earth Sciences, 14, 7-23. centres. The depocentre of the basin is located between the MacGillycuddy's Reeks and the Kenmare River on the Iveragh peninsula where the succession is at least ca.
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Kylander-Clark, A., Hacker, B., and Mattinson, C., 2012, Size and exhumation rate of ultrahigh-pressure terrains linked to orogenic stage: Earth and Planetary Science Letters, v. 321-322, p. 115-120. All are dominated by quartzofeldspathic gneiss with a few percent mafic rock (eclogite) or ultramafic rock (garnet-bearing peridotite). Some include sedimentary or rift-volcanic sequences that have been interpreted as passive margins prior to metamorphism.
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The sandstone is well-cemented and contains no glacial deposits and no fossils. The grains of Jacobsville Sandstone range from in size. Based on an average from samples taken in Marquette and Alger counties, Jacobsville Sandstone is composed of: 27.4% nonundulatory quartz, 27.0% undulatory quartz, 23.0% potassium feldspar, and 12.3% silicic volcanic clasts. Smaller constituents are 3.8% polycrystalline quartz, 2.4% metamorphic, 1.4% sedimentary, 1.3% opaque, 0.8% mafic volcanic, and 0.1% plagioclase.
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Felsic metavolcanic rocks and mafic intrusive rocks are cut by silicified zones and veins. A zone of diorite with a maximum width of has been assayed to have up to of gold per ton. A sulfide-rich vein has been assayed to have of gold per ton and of silver per ton. Trenches, open pits and stripped areas are present in the Temagami Occurrence from past mining operations.
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Latest estimates (April 2009) report that Donlin contains 29.3 million ounces of proven and probable gold reserves (calculated at a gold price of $750) and an additional 10 million ounces of gold resource. The gold occurs within the crystal lattice of arsenopyrite associated with other metal sulfides in veins, veinlets, and disseminations mainly in the felsic dikes, but also in less common altered mafic dikes and in the sediments.
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The 2,125- to 2,090-million-year-old mafic magmatic events affecting the Superior and Wyoming cratons show the hotspot having moved west from Sudbury, and the two provinces have rifted so that they are separated by . That narrowest distance between the two cratons is from Sudbury, in east- central South Dakota. The Blue Draw Metagabbro is now west of Sudbury and south of the Superior province's southern border.
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Fumarole activity near Jigokunuma. The Hakkōda Mountains are two clusters of stratovolcanoes in the Northeastern Japan Arc that consists of lava flows, debris flows, and pyroclastic ejecta and flows arranged into southern and northern groups. The volcanic peaks are made of non-alkali mafic rock; mostly andesite, dacite, and basalt. Although both groups of mountains formed in the Pleistocene, the southern group is older than the northern group.
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The Purcell Supergroup is composed primarily of argillites, carbonate rocks, quartzites, and mafic igneous rocks of late Precambrian (Mesoproterozoic) age. It is present in an area of about 15,000 km2 (5,800 sq. mi.) in southwestern Alberta and southeastern British Columbia, Canada, and it extends into the northwestern United States where it is called the Belt Supergroup. It was named for the Purcell Mountains of British Columbia by R.A. Daly in 1912.
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The mountain comprises two principal components: a voluminous basal shield volcano and an eroded stratovolcano cap. The lower but more extensive basal shield volcano rises from an elevation of above the surrounding forested lowlands much like an inverted dishware plate. It consists of four distinctive stratigraphic units comprising thin mafic lava flows. Individual flows have an average thickness of but can range from less than to more than thick.
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1450–1430 Ma. This was evidenced by the protolith of the Group, being interlayers of clastic-sedimentary rocks, pyroclastic and volcanic rocks which were mafic to intermediate in nature. The regional metamorphism experienced by the Baoban Group was caused by the South China Jinningian event in which the Cathaysia Block fused with the Yangtze Block in Late Mesoproterozoic. The event also led to deposition of Shilu Group and Shihuiding Formation.
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The filled and solidified magma chamber of Torres del Paine (Patagonia) is one of the best exposed laccoliths, built up incrementally by horizontal granitic and mafic magma intrusions over 162 ± 11 thousand years. Horizontal sheeted intrusions were fed by vertical intrusions. The small Barber Hill syenite- stock laccolith in Charlotte, Vermont, has several volcanic trachyte dikes associated with it. Molybdenite is also visible in outcrops on this exposed laccolith.
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The Nuvvuagittuq Greenstone Belt (NGB) is a sequence of metamorphosed mafic to ultramafic volcanic and associated sedimentary rocks (a greenstone belt) located on the eastern shore of Hudson Bay, 40 km southeast of Inukjuak, Quebec. These rocks have undergone extensive metamorphism, and represent some of the oldest rocks on Earth. Two papers dating the age of the Nuvvuagittuq Greenstone Belt have been published. One paper gave an age of ca.
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The Circum- Superior Belt is the host for widespread mineral deposits, including copper, nickel and platinum group elements. However, the origins of this widespread mineralization is unknown. The Thompson Belt in Manitoba is one of the most comprehensive nickel producing zones on Earth. It has the potential to contain platinum group elements, but the age of the mafic-ultramafic volcanic rocks comprising the nickel deposits are not well known.
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The date of the docking is unknown, but could have occurred during the Taconic, Acadian, or Alleghanian Orogenies. The terrane comprises Neoproterozoic to Early Cambrian meta-sedimentary and meta-igneous rocks, intruded by later Paleozoic plutons. The protoliths of the meta-igneous rocks include mafic, intermediate, and felsic volcanics and plutons. These rocks underwent at least four metamorphic/deformation events, and so their original textures and mineralogies have been significantly altered.
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Outside of the rift basin and east and west of Lake Nipigon, the Sibley Group is absent and erosion resistant Archean rocks are either exposed at the surface or blanketed by Pleistocene glacial sediments.Hart, T.R. and MacDonald, C.A., 2007. Proterozoic and Archean geology of the Nipigon Embayment: implications for emplacement of the Mesoproterozoic Nipigon diabase sills and mafic to ultramafic intrusions. Canadian Journal of Earth Sciences, 44(8), pp.1021-1040.
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The Archean and Proterozoic strata are intruded by a number of mafic and ultramafic intrusions, which define the current outline of the Nipigon Embayment. They consist of relatively flat-lying and undeformed diabase sills known as the Nipigon diabase sills. These sills range in thickness from a few meters to thick in cliff sections to more than thick in drill core. They are estimated to cover an area in excess of .
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The former are particularly represented east of Cerro Blanco and go back in part to the Precambrian, the latter occur mainly west and consist of Ordovician volcano- sedimentary units. Both are intruded by granitoids and mafic and ultramafic rocks. Permian sediments and Paleogene rocks complete the nonvolcanic geology. Local tectonic structures such as borders between crustal domains and northeast-southwest trending faults might control the position of volcanic vents.
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Low viscosity permits rapid nucleation and ion migration, necessary for crystal formation. The high silica content of rhyolitic lavas gives them much higher viscosities. Such lavas tend to form glass (obsidian) when they cool rapidly from a fully melted liquid state; though many obsidians also contain microlites. Low viscosity mafic magmas must be quenched very rapidly from a high temperature to form glass that is free of any crystalline content.
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Medicine Lake Volcano began to grow about one million years ago in Pleistocene time, following the eruption of a large volume of tholeiitic high-alumina basalt. Similar high-alumina basalt has continued to erupt around the volcano throughout its history. Although mafic lavas predominate on the volcano's flanks, all lava compositions from basalt to rhyolite have erupted during Pleistocene time. The lower flanks consist of mostly basaltic and some andesitic lavas.
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The andesite line is the most significant regional geologic distinction in the Pacific Ocean basin. It separates the mafic basaltic volcanic rocks of the Central Pacific Basin from the partially submerged continental areas of more felsic andesitic volcanic rock on its margins. The andesite line parallels the subduction zones and deep oceanic trenches around the Pacific basin. It is the surface expression of melting within and above the plunging subducting slab.
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Delamination is seen in convergence zones, especially where continental-continental collisions occur. For example, delamination is seen in the Tibetan Plateau, which has formed from the collision of India with Asia. Observations which support delamination include sudden mafic volcanism and acceleration of uplift, occurring 14 to 11 Ma. Areas of extension are also associated with delamination. Negative buoyancy of the lower lithosphere drives delamination in both environments of collision and extension.
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South of the Zimbabwe Craton is the Kaapvaal Craton separated from it by the Limpopo Mobile Belt, a zone of deformation and metamorphism reflecting geological events from Archean to Mesoproterozoic times. The Zimbabwe Craton is intruded by an elongate ultramafic/mafic igneous complex known as the Great Dyke which runs for more than 500 km along a SSW/NNE oriented graben. It consists of peridotites, pyroxenites, norites and bands of chromitite.
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Gold production came from underground lode mines exploiting: gold-bearing quartz veins in metamorphic rocks (such as the Gold Standard, Sea Level, Dawson, Golden Fleece and Goldstream mines); skarns (at the Jumbo and Kassan Peninsula copper-gold mines); zoned mafic-ultramafic plutons, as at the Salt Chuck silver-gold- copper-PGE mine; and VMS deposits such as Niblack. Uranium was mined at Bokan Mountain in the 1950s and 1970s.
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The geological type area for labradorite is Paul Island near the town of Nain in Labrador, Canada. It has also been reported in Norway, Finland and various other locations worldwide, with notable distribution in Madagascar, China, Australia, Slovakia and the USA. Labradorite occurs in mafic igneous rocks and is the feldspar variety most common in basalt and gabbro. The uncommon anorthosite bodies are composed almost entirely of labradorite.
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Fenite is a metasomatic alteration associated particularly with carbonatite intrusions and created, very rarely, by advanced carbon dioxide alteration (carbonation) of felsic and mafic rocks. Fenite alteration is known, but restricted in distribution, around high-temperature metamorphic talc carbonates, generally in the form of an aureole around ultramafic rocks. Such examples include biotite-rich zones, amphibolite-calcite-scapolite alteration and other unusual skarn assemblages. The process is called fenitization.
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Llullaillaco has mostly erupted dacites with medium potassium content, with rocks becoming more felsic the younger they are. Rock samples taken from Llullaillaco are mostly porphyritic or vitrophyric, with a glassy or microcrystalline matrix. Phenocrysts are mostly plagioclase, with mafic phenocrysts being dominated by orthopyroxene and smaller amounts of biotite, clinopyroxene, and hornblende. Ilmenite, magnetite, and sulfide minerals are also present, magnetite especially in the more oxidized older lavas.
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About 2 million years ago, the "Diaguita deformation" was characterized by a change in the deformation regimen from crustal shortening to strike-slip faulting and of volcanism from voluminous felsic eruptions to isolated stratovolcanoes and back-arc mafic volcanism. A slowdown in the subduction may have caused this change. Nowadays most volcanism occurs at the western edge of the Puna, where volcanoes such as Lascar and Llullaillaco formed.
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Hafnium is a substituting impurity and may be present in quantities ranging from 0.1 to several percent. It can be found in igneous rocks containing potassium feldspar and plagioclase. Baddeleyite is commonly not found with zircon (ZrSiO4), because it forms in silica-undersaturated rocks, such as mafic rocks. This is because, when silica is free in the system (silica-saturated/oversaturated), zircon is the dominating phase, not baddeleyite.
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Horseshoe Falls, part of the Niagara EscarpmentCaprock is a harder or more resistant rock type overlying a weaker or less resistant rock type. Common types of caprock are sandstone and mafic rock types. An analogy of caprock could be the outer crust on a cake that is a bit harder than the underlying layer. In processes such as scarp retreat, the caprock controls the rate of erosion of the scarp.
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The mafic-ultramafic igneous rocks formed due to underplating with crustal stretching during Carboniferous to Permian. The magma underplating during Carboniferous to Permian (330-250 Ma) period heated up the lower crust and thus the crust got hotter. The following cooling crustal episode led to part of the mountain belt sink by thermal subsidence, which ended up forming the Junggar Basin. Another magma underplating event occurred in the Mesozoic era.
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Luxi Complex, also known as the Luxi granite-greenstone terrane in western Shandong, contains gneiss and sheets and lenses of metamorphosed ultramafic- mafic volcanic rocks (greenstone). Metamorphosed komatiite was discovered as serpentinized peridotite and schist with spinifex texture. Such texture is interpreted to be associated with a basaltic volcanic activity 2.74 billion years ago. Similarly, in Qixia, 2.75–2.7 billion-year-old gneiss of Qixia Complex was seen.
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Beiiing: Geological Publishing Housh (in Chinese). The ultramafic to mafic rocks in the North Liaohe group in eastern Liaoning were formed behind the arc where the crust spread (back-arc basin). Later, the Langrim block moved over the lower Longgang block and brought the South Liaohe group to the Belt. Unfortunately, calc-alkaline rocks, which are commonly generated in magmatic arc system, were not found in the area.
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Carmichael, Turner and Verhoogen, 1974, Igneous Petrology, McGraw-Hill, pp. 603–620Hyndman, Donald W., 1972, Igneous and Metamorphic Petrology, McGraw-Hill, pp. 122–139, esp. references. Norite occurs with gabbro and other mafic to ultramafic rocks in layered intrusions which are often associated with platinum orebodies such as in the Bushveld Igneous Complex in South Africa, the Skaergaard igneous complex of Greenland, and the Stillwater igneous complex in Montana.
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Granite is a felsic rock, meaning it is rich in potassium feldspar and quartz. This composition is continental in origin (meaning it is the primary composition of the continental crust). Since it cooled relatively slowly, it has large visible crystals. Basalt, on the other hand, is mafic in composition—meaning it is rich in pyroxene and, in some cases, olivine, both of which are Mg-Fe rich minerals.
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Probably a similar type of eruption: Memorial of jökulhlaup over Skeiðarársandur following the Grímsvötn-Gjálp eruption in 1996 Sveifluháls from Seltún geothermal area Sveifluháls seen from Grænavatn maar Sveifluháls is a mafic hyaloclastite ridge of 397 m height in the southwest of Iceland in Gullbringusýsla (Reykjanes Peninsula).Íslandshandbókin. Náttúra, saga og sérkenni. Reykjavík 1989, p. 62 It is part of Krýsuvík volcanic system and of the protected area Reykjanes Fólkvangur.
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Since the late Oligocene, subduction of the Nazca Plate beneath the South America Plate has caused volcanism on the western edge of South America, including the formation of the Central Volcanic Zone. The crust in the Central Andes contains both an upper felsic layer and a lower mafic layer and was partly assembled from numerous terranes during the Mesoproterozoic. The most important two form the Arequipa-Antofalla crustal domain.
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Sturgeon Lake Caldera is a large extinct caldera complex in Kenora District of Northwestern Ontario, Canada. It is one of the world's best preserved mineralized Neoarchean caldera complexes, containing well-preserved mafic- intermediate pillow lavas, pillow breccias, hyaloclastite and peperites, submarine lava domes and dome-associated breccia deposits. The complex is some 2.7 billion years oldCaldera Volcanoes Retrieved on 2007-07-20 with a minimum strike length of .
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This plug is made of micronorite with a diameter of . There are dikes exposed throughout the summit cone, mostly oriented from north to south, with another dike swarm trending north from the central plug. The summit formed over a platform of basaltic andesite lavas from early eruptions at Mount Washington, made of thinner flows combined with pyroclastic rock. The volcano has a mafic composition, with subalkaline basalt and basaltic andesite.
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Emi Koussi has erupted phonolite, trachyandesite and trachyte, as well as mafic rocks like basanite and tephrite. The erupted rocks define two alkaline suites. Phenocryst chemistry and content varies between the various rocks; among the minerals are alkali feldspar, amphibole, biotite, clinopyroxene, olivine, oxides and plagioclase. Alkali feldspar, apatite, clinopyroxene, olivine, magnetite, mica, nepheline, oxides, plagioclase, quartz, sodalite, titanite and zircon also form the groundmass of microliths in erupted rocks.
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Clay minerals are hydrous aluminum phyllosillicates and form only in the presence of water, further supporting the claim that an ancient crater lake once existed in this region. Other silicates were detected as well, such as the Magnesium-rich end-member of olivine called forsterite, pigeonite, plagioclase, augite, clinopyroxene, and orthopyroxene. These detected minerals are all indicative of a potential mafic source for the origin of the deposition.
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The rock is an uncommon mafic igneous rock known as a troctolite. It is black with phenocrysts of plagioclase in a medium grained matrix of magnetite, ilmenite, olivine and hercynite spinel. The abundance of magnetite and ilmenite, which may be up to 70 percent of the rock, is responsible for the high density and magnetic property. Locally the parallel orientation of the lathlike plagioclase crystals gives the rock a flow lamination.
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Most of the zone has been through granulite facies metamorphism and was intruded by mafic plutons. This is the type of rock common in the lower regions of the crust. When the terrane was uplifted during the formation of the Alps, the upper crust was eroded off so that these rocks are now at the surface. Geophysical research shows the mantle is relatively close under the surface at the Ivrea zone.
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The magmatic evolution of the basalts is dominated by low pressure crystal fractionation from olivine, chromium-spinel, plagioclase, and clinopyroxene. The basalts can be split to form two subprovinces based on concentration of incompatible elements and geographical position. The western subprovince is composed of mafic and intermediate rocks. They have a low abundance of high field strength elements, negative Nb anomalies, and a wide range of initial 144Nd/143Nd.
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Biotite compositions from S-type granites are more aluminous than those of I-type granites consistent with the higher ASI index of S-type Granites. Figure 2b. Plane polarized light photomicrograph showing garnet and biotite in sample CV-126 from the mafic S-type Strathbogie Granite, Australia. Figures 3a and 3b are photomicrographs of thin sections of sample CC-1 from the Cooma Granodiorite, Lachlan Fold Belt, Australia.
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It grows along the banks in cracks in the mafic bedrock. It can also anchor in concrete at the bases of local dams. It is sometimes subjected to scouring by floodwaters. It may grow alongside other plants, including Virginia pine (Pinus virginiana), winged elm (Ulmus alata), sweet-gum (Liquidambar styraciflua), sparkleberry (Vaccinium arboreum), false indigo (Amorpha fruticosa), little bluestem (Schizachyrium scoparium), orangegrass (Hypericum gentianoides), and white false indigo (Baptisia alba).
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The district is located within a Middle Jurassic volcano-plutonic complex composed of basaltic lavas and volcaniclastics underlain and intruded by gabbroic rocks. Mafic dikes are abundant and form sheeted dike swarms. Deposition of iron was not associated with silicification or sulfidation. Host rocks contain veins and large accumulations of pure magnetite in structural or breccia zones, or are impregnated with clots of magnetite in all size ranges.
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These are overlain by thick mafic alkaline lava flows and at least 30 small cinder cones. Hawaiite is the dominant rock type, but alkali olivine basalt and spinel lherzolite-bearing basanite is also present. They merge laterally with lavas of the much older Chilcotin Group, which surrounds the Anahim Volcanic Belt. However, the exact nature of the relationship between the Anahim Volcanic Belt and the Chilcotin Group is unknown.
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This period is characterized by the intrusion of mafic-ultramafic sills, meimechite and carbonatite deposition, and MORB-like mafic volcanism corresponding to the formation of a transitional continental-oceanic crust. # A deformation and high-grade metamorphism phase occurs in the hinterland near Kuujjuaq from 1.84 to 1.83 Ga. A regional-scale granitic and charnockitic intrusion, the De Pas Supersuite (formerly De Pas Batholith), was also emplaced during the same period and up to 1.81 Ga. This supersuite is interpreted by several authors as being associated with a Proterozoic magmatic arc environment connected to a subduction zone developed during the orogenesis. This supersuite may also be associated with a syncollisional component in the hinterland. # There would have been an oblique collision between the Superior craton and the Core Zone of the Churchill Province during the orogenesis from 1.82 to 1.77 Ga. This event resulted in transpressure-type deformation and the formation of a western-verging thrust and fold belt, now known as the Labrador Trough.
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Dates on two samples from Sheffield Heights indicate that the diorite and granite are part of the Dedham North suite. The Dedham south and west of Boston has been dated at 630+/15 Ma. Dedham North Granite has a compositionally highly variable suite ranging from leucogranites to granodiorites, tonalites, and quartz diorite. The granites originated by partial melting of a sedimentary protolith, while the intermediate members show a mixing of granitic magma and mafic magma.
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It features well developed levees and a flow front. Its rocks have a pale gray-blue colour, and their composition resembles the Soncor flow, despite more mafic lavas and pyroclastics being erupted in the time period between the emplacement of the Soncor flow and the Capricorn Lava. An early pyroclastic flow, the Saltar Flow, is exposed on the eastern flank. It was emplaced after the collapse of the oldest edifice, covering Aguas Calientes' western slopes.
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The Piedras Grandes unit is over 26,500 years old, possibly between 63,000 and 100,000 years old. Temperatures have been estimated to be for the andesite and for the basaltic andesite. The magmas were formed from a remelted proto-pluton that had been heated and resupplied with volatiles by mafic magmas. The lava domes interacted with glaciers, resulting in the formation of a glacier run whose deposits are found as far as from the volcano.
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Cumulate rocks are the typical product of precipitation of solid crystals from a fractionating magma chamber. These accumulations typically occur on the floor of the magma chamber, although they are possible on the roofs if anorthite plagioclase is able to float free of a denser mafic melt. Cumulates are typically found in ultramafic intrusions, in the base of large ultramafic lava tubes in komatiite and magnesium rich basalt flows and also in some granitic intrusions.
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The Fowler Domain is a major tectonic zone on the north-western flank of the Gawler Craton comprising dense, magnetic, highly deformed, intermediate to ultramafic intrusives overlain by thin Tertiary sands and recent sand dunes. Aeromagnetic surveys show the presence of a high concentration of crustal scale fractures and faults in this area. These structures could have provided pathways for the intrusion of mafic-ultramafic bodies with potential for nickel sulfides, chromite and platinoids.
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Some amphibolite layers record the metamorphosed remains of a tholeiitic magma series. The early folding and metamorphism in the Ibadan area was followed by the emplacement of aplite schist and microgranodiorite dikes during the Liberian orogeny 2.75 billion years ago. More intense deformation followed 2.2 billion years ago during the Eburnean orogeny. Metazquartzites in the Ibadan area, likely from the Proterozoic, are overlain by pelite schist, intruded by mafic sills rich in magnesium.
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The Central Felsic Complex (CFC), centers on Green Mountain and Middleton Ridge and is older than the Eastern Felsic Complex. Here, ash is typically welded together and breccia is laden with rhyolite and obsidian fragments. Middleton Ridge formed more than one million years ago and is accompanied trachyte and rhyolite flows. By comparison, Green Mountain formed as recently as 395,000 years ago with trachyte flows and pyroclastics grouped around a mafic scoria cone.
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Faults such as the Troncoso Fault lie within the southwestern sector of the volcanic field. Troncoso is alternatively described as a strike-slip or as a normal fault; it separates distinct regimes of tectonic and volcanic activity within the Laguna del Maule volcanic field. Other north–south cutting faults are found within the Campanario Formation. Northeast of Laguna del Maule is the Cerro Campanario, a mafic stratovolcano that is high and was active ago.
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The concession covers of the Kilo-Moto goldfields. It includes the Karagba-Chaffeur-Durba (KCD) deposit complex and the satellite Sessenge, Pakaka, Pamao, Gorumbwa, Kibali, Mengu Hill, Mengu Village, Megi, Marakeke, Kombokolo, Sessenge and Ndala deposits. It is in the Moto greenstone belt, which contains Archean volcano-sedimentary, pyroclastic and basaltic rocks, with mafic and felsic intrusions. There are two zones: Kibali-Durba-Karagba trends north-east, and Pakaka-Mengu trends north-west.
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Geologists believe that igneous oceanic plateaus may well represent a stage in the development of continental crust as they are generally less dense than oceanic crust while still being denser than normal continental crust. Density differences in crustal material largely arise from different ratios of various elements, especially silicon. Continental crust has the highest amount of silicon (such rock is called felsic). Oceanic crust has a smaller amount of silicon (mafic rock).
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Shonkinite is an intrusive igneous rock. More specifically, it is a mafic foidal (feldspathoid bearing) syenite, a holocrystalline (completely crystalline) intrusive rock which, , is composed of potassic feldspar in the form of sanidine, nepheline, augite, biotite, and olivine.Weed, Walter H. and Pirsson, Louis V. Geology of the Little Belt mountains, Montana, With Note on the Mineral Deposits of the Neihart, Barker, Yogo, and Other Districts. Washington, D.C.: Government Printing Office, 1900, p. 319.
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Shonkinite is also used for mafic nepheline syenite with aegerine- augite as the pyroxene, and with the addition of plagioclase (andesine to labradorite). Nepheline in shonkinite from the is largely altered to natrolite and stilbite. The close view of the rocks in the Adel mountains show large glossy crystals of augite in a dark grey matrix made up of small crystals of augite and feldspar. This is unusual as augite is usually dull.
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Photometric observations of this asteroid at the Organ Mesa Observatory in Las Cruces, New Mexico during 2010 gave an irregular light curve with a period of 34.407 ± 0.002 hours and a brightness variation of 0.05 ± 0.01 in magnitude. A 2004 study of the spectrum matched a typical C-type asteroid with typical carbonaceous chondrite makeup. There are no absorption features of mafic minerals found. The classification was later revised to a P-type asteroid.
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Image is about 1.5 km wide. In this enhanced-color image, the blue and green colors are generally due to mafic (magnesium and iron rich) minerals that are not altered by water, while the warmer colors are due to altered minerals like clays. The structure in this scene is complex, from impact and perhaps fluvial and volcanic processes, tectonic faulting, and erosion. This is an old terrain with a complex geologic history.
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Geologic map of the Belt Supergroup in Idaho The Belt Supergroup is an assemblage of primarily fine-grained sedimentary rocks and mafic intrusive rocks of late Precambrian (Mesoproterozoic) age. It is more than thick, covers an area of some 200,000 km2 (77,220 sq. mi), and is considered to be one of the world's best-exposed and most accessible sequences of Mesoproterozoic rocks. It was named after the Big Belt Mountains in west-central Montana.
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In rocks with extremely low aluminium contents, this reaction can progress to create magnesite. Advanced carbonation of felsic and mafic rocks, very rarely, creates fenite, a metasomatic alteration caused particularly by carbonatite intrusions. Fenite alteration is known, but very restricted in distribution, around high-temperature metamorphic talc-carbonates, generally in the form of a sort of aureole around ultramafics. Such examples include biotite-rich zones, amphibolite-calcite- scapolite alteration and other unusual skarn assemblages.
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Mount Asama sits at the conjunction of the Izu-Bonin-Mariana Arc and the Northeastern Japan Arc. The mountain is built up from non-alkali mafic and pyroclastic volcanic rocks dating from the Late Pleistocene to the Holocene. The main rock type is andesite and dacite. Viewed from the north Scientists from the University of Tokyo and Nagoya University completed their first successful imaging experiment of the interior of the volcano in April 2007.
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Silica-undersaturated igneous rocks typically are formed by low degrees of partial melting in the Earth's mantle. Carbon dioxide may dominate over water in source regions. Magmas of such rocks are formed in a variety of environments, including continental rifts, ocean islands, and supra-subduction positions in subduction zones. Nepheline syenite and phonolite may be derived by crystal fractionation from more mafic silica-undersaturated mantle-derived melts, or as partial melts of such rocks.
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An episode of hotspot gabbro magmatism occurred at the eastern edge of the Wyoming craton, south of current-day Sudbury. Continental rifting is exhibited by emplacement of mafic igneous rocks on each side of the rift margins. By the Superior and Wyoming provinces had completely separated. From about 2,100 to 1,865 million years ago the Wyoming craton drifted in a westward direction until it docked with the Superior province, northwest of its original position.
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This stage of activity is characterized by small volumes of more mafic lavas expressed as small cinder cones and capping flows. Dissection of the shield by stream erosion is also apparent, resulting in the creation of deeply incised radial valleys. Prolonged erosion eventually removes most if not all traces of the volcanoes to expose their underlying solidified magma systems. Such systems can be below the surface with rocks ranging from hypabyssal to plutonic.
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The Hearne Craton and Rae Craton are underlain by Archean metasedimentary and metavolcanic rocks. Quartz arenite in the Rae Craton has been interpreted as possible passive margin or rift deposits. Around the world, greenstone belts are a hallmark of ancient Precambrian rocks. The Ennadai-Rankin greenstone belt is the second largest in Canada and displays felsic volcanic and volcaniclastic rocks, as well as mafic rocks reaching greenschist grade on the sequence of metamorphic facies.
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The Nuvvuagituq Belt is bounded by eoarchean tonalites, trondhjemites and granodiorite aged around 3660 Ma, and further surrounded by younger approximately 2750 Ma tonalities. Surrounding tonalites, trondhjemites and granodiorites (TTGs) are the product of partial melting of Hadean Mafic lithologies, which was similar to the Ujaraaluk unit. The remelt products of "Hadean Ujaraaluk" and the exposed, eoarhcean Ujarraluk unit share similar geochemical composition i.e. isotopic ratio between 142-Neodymiun to 144-Neodymium.
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Insulated by the overlying roof rock, upwelling magma cooled slowly, and the mafic rock into which it cooled therefore is coarse-grained. These intrusions formed a sill some 16 km thick,Ojakangas & Matsch (1982), pp. 55–57. primarily of gabbro, but with significant amounts of anorthosite and other related granitic rocks.Jirsa & Southwick, Mineral Potential (2000); Topinka, America's Volcanic Past (2003); Miller, Green, Severson, Chandler, & Peterson, Geologic Map of the Duluth Complex (2001).
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Restite is the residual material left at the site of melting during the in place production of granite through intense metamorphism. Generally, restite is composed of a predominance of mafic minerals because these are harder to melt (see Bowen's reaction series). Typical minerals are amphibole, biotite, pyroxene, ilmenite or other iron oxides and some plagioclase feldspar. When chunks of restite are caught up within the granite it is known as a restite inclusion or enclave.
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Restite reactions in I-type granites are essentially similar, but due to the mafic and granitic source rocks, the restite assemblage is predisposed to produce an orthopyroxene + clinopyroxene + plagioclase +/- garnet assemblage. Similar to the reactions occurring in S-type granites, the restite minerals will revert to hornblende and plagioclase upon ascent, resorbing water and precluding generation of hydrothermal solutions. Porphyry copper deposits are generally associated with I-type granites which are not restite mediated.
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In Northern Portugal, along the Vigo-Régua Shear Zone, the monzogranites belong to the syn-F3 biotite granitoid group. They present a porphyritic texture (potassium feldspar megacrysts) and mafic microgranular enclaves that decrease in frequency from South to North. The granites are composed of quartz + potassium feldspar + plagioclase (andesine/oligoclase) + biotite + zircon + monazite + apatite + ilmenite ± muscovite. The studied granodiorites-monzogranites are moderately peraluminous, [(A/KNC)m:1.19–1.39], with SiO2 contents between 62 and 70%.
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Greens Creek Mine Metal sulfides were deposited by hydrothermal fluids on or in the sea floor of a tectonically-active basin. The deposit exhibits features of both VMS and SEDEX models. Most of the ore body is zinc-lead-silver-gold-barium rich; some zones have elevated copper values. The deposit is hosted in metamorphosed, multiply deformed, and hydrothermally-altered mainly marine Triassic sediments and mafic volcanic rocks within the exotic Alexander terrane.
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Volcanic surface manifestation of the Great Dyke event has not been recorded and have probably been eroded. The Great Dyke is a strategic economic resource with significant quantities of chrome and platinum. Chromite occurs to the base of the Ultramafic Sequence and is mined throughout the dyke. Below the Ultramafic-Mafic sequences' contact, and in the uppermost pyroxenite (bronzitite and websterite) units are economic concentrations of nickel, copper, cobalt, gold, and platinum group metals (PGM).
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The rocks were deformed and metamorphosed before emplacement of syntectonic diatexites (ca 2.66-2.68 Ga). The diatexites could be the product of fusion of the paragneisses of the Opinaca Subprovince and some of the tonalities and mafic gneisses of the La Grande Subprovince. Later intrusions of felsic granitoids (ca 2.63-2.64 Ga) cut the diatexites and their surrounding gneisses. The region has promise as a source of minerals, and several gold mineralizations have been found.
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In the US state of Virginia, it can be found growing in rocky woodlands, barrens, and crevices or thin-soiled ledges on outcrops of limestone, dolomite, siltstone, metasiltstone, amphibolite, metabasalt, diabase, and other mafic and felsic igneous and metamorphic rocks. It is also located in areas of the eastern United States where it is usually limited to sand bars. In Europe it has been found in southern Germany and restricted areas of Sweden.
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Nickel deposits are generally found in two forms, either as sulfide or laterite. Sulfide type nickel deposits are formed in essentially the same manner as platinum deposits. Nickel is a chalcophile element which prefers sulfides, so an ultramafic or mafic rock which has a sulfide phase in the magma may form nickel sulfides. The best nickel deposits are formed where sulfide accumulates in the base of lava tubes or volcanic flows -- especially komatiite lavas.
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The Isua Greenstone Belt is an Archean greenstone belt in southwestern Greenland. The belt is aged between 3.7 and 3.8 billion years. The belt contains variably metamorphosed mafic volcanic and sedimentary rocks. The occurrence of boninitic geochemical signatures, characterized by extreme depletion in trace elements that are not fluid mobile, offers evidence that plate tectonic processes in which lithic crust is melted may have been responsible for the creation of the belt.
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The Dufek Intrusion is a mafic layered intrusion that was emplaced into present-day Antarctica approximately 183 million years ago.S.D.Burgess, S.A.Bowring, T.H.Fleming & D.H.Elliot, 2015. High-precision geochronology links the Ferrar large igneous province with early-Jurassic ocean anoxia and biotic crisis. Earth and Planetary Science Letters, , Vol: 415, Page: 90-99 It comprises two outcropping sections called the Dufek Massif and the Forrestal Range that are thought to be connected beneath the Sallee Snowfield.
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Changes in the concentration of nitrogen in the will affect the growth performance of K. serotina; however, limited information is known about the species' soil nutrient requirements. The plant can tolerate dry soil conditions, twhichhat enables it to perform better than native forest. According to Olsen, it is found in areas where the soil is free-drained, with different soil types, from sand and loam to alluvium, sedimentary and ultra- mafic rock.
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The basement rock of Lithuania is made up of the West Lithuanian Granitic Massif aluminous schist, metabasic rocks (reaching granulite grade on the sequence of metamorphic facies) and gneiss and the Southeast Lithuanian Zone granitoids, plagiomicrocline granite and migmatite. The massif has some notable Mesoproterozoic dike swarms. In the southeast, granitoids alternate with metagraywacke, amphibolite and rare dolomite marble, mica-schist. Metamorphic rocks typically reach amphibolite facies and ultramafic or mafic intrusions are common.
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The nearly vertical lode strikes east-northeast (N 065) and is enclosed in the southern rim facies of the Piégut-Pluviers Granodiorite. Only a mere 1000 meters farther to the southeast country rocks (plagioclase-bearing paragneisses) are already encountered. The host granodiorite appears in its darker, finer-grained hornblende facies with amphibole and biotite. The rim facies has a much more mafic chemistry than the ordinary, coarser-grained facies to the North.
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As well, a much older group of totally unrelated volcanic rocks comprise the Stikine Assemblage, which also mainly occurs within the geographic area informally referred to as Stikine Country. The Northern Cordilleran Volcanic Province is a broader name, to encompass a broader geographic area, in which the most recent volcanism has a similar character (mainly alkaline, mafic volcanic rocks), a similar age range (Miocene to Holocene), and a similar tectonic setting (transtension).
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The terrain along the bottom is hilly in the southern half while the north is relatively smooth. The central peaks consist of three isolated mountainous rises climbing as high as 1.2 km above the floor. These peaks are separated from each other by valleys, and they form a rough line along an east–west axis. Infrared observations of these peaks during the 1980s determined that they were primarily composed of the mafic form of olivine.
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733 and as an accessory mineral in alkaline and mafic igneous rocks, nepheline syenite, melilitite, kimberlites and rare carbonatites. Perovskite is a common mineral in the Ca-Al-rich inclusions found in some chondritic meteorites. A rare- earth-bearing variety knopite ((Ca,Ce,Na)(Ti,Fe)O3) is found in alkali intrusive rocks in the Kola Peninsula and near Alnö, Sweden. A niobium-bearing variety dysanalyte occurs in carbonatite near Schelingen, Kaiserstuhl, Germany.
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S-type granites, like other granite types, can vary in crystal size from aphanitic to phaneritic; crystal size distributions include porphyritic, seriate, and rarely equigranular textures. Mafic xenoliths/enclaves can be found in S-type granites. Granophyric textures can be found in S-type granites, particularly leucocratic ones. In porphyritic S-type granites, phenocrysts are commonly feldspars, but can also be quartz, and in rare cases, such as the Strathbogie Granite, cordierite.
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Geology of the mountain has been studied since 1902. The mountain formation has been reported to be an igneous sedimentary rock formation with granite (in a limited area of ), felsic and mafic dykes. Granites in the southwest face of the mountain contain Zeunerite, a form of uranium. Its age is conjectured to be Mesozoic with intrusions of black slate formations which are in turn dated to the formations of the Cambrian and Pre- Cambrian age.
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Black Butte is well-preserved due to a lack of glaciation east of the major Cascade arc. Black Butte has undergone mild erosion, with shallow ravines on its slopes, deep gullies on its sides, and rocks with weathering rinds. Black Butte forms a steep-sided volcanic cone, with an unexposed pyroclastic core and no summit crater. It is one of the larger mafic volcanic cones in the Oregon Cascades, with a volume of .
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Crustal contamination can be inferred from samples taken from two cones, and small isotopic variations for the other cones indicate at least three mantle components. The primitive magmas differ from other reported intraplate-type mafic alkalic suites by having relatively high Al2O3 and Yb, as well as low ratios of La/Yb and CaO/Al2O3. Rising Al2O3 and falling CaO, along with decreasing incompatible element abundances, are consistent with progressive partial melting.
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Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene, feldspathoids and other unusual minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions. Crystal size is the most striking feature of pegmatites, with crystals usually over 5 cm in size. Individual crystals over long have been found, and many of the world's largest crystals were found within pegmatites. These include spodumene, microcline, beryl, and tourmaline.
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Beach pebble of variolitic pillow lava (varolite) from the Olympic Peninsula, Washington state Variolites are mafic, igneous, and typically volcanic rocks, e.g. tholeiite, basalt or komatiite, that contain centimeter-scale spherical or globular structures, called varioles, in a fine-grained matrix. These structures are lighter colored than the host rock and typically range in diameter from 0.05mm to over 5 cm.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) Glossary of Geology (5th ed.).
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Under its northeast edge, Calabozos is cut by a north-south trending segment of sedimentary rock that includes gypsiferous and carbonates. Calabozos is similar in age to Cerro Azul and Descabezado Grande, and its eruptions may correspond to past activity at both volcanoes. Eruption products of very similar composition (including mafic andesite, agglutinates, and dacite) make up the volcanoes. There is also a similarity in size (all are between 40 and 70 cubic kilometers in volume).
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However, they are formed by the same processes and accumulate due to their high specific gravity, and can form laterally extensive sulfide 'reefs'. The sulfide minerals generally form an interstitial matrix to a silicate cumulate. Sulfide mineral segregations can only be formed when a magma attains sulfur saturation. In mafic and ultramafic rocks they form economic nickel, copper and platinum group (PGE) deposits because these elements are chalcophile and are strongly partitioned into the sulfide melt.
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Isluga's lavas are andesitic to trachyandesitic in composition with SiO2 contents between 56-61%. The andesites are porphyritic with more than half phenocrysts and high potassium content (2.7-3.6%), moderate aluminium and high magnesium, although some hornblendes have high Na/K ratios. The petrology of the Isluga lineament lavas indicates an origin either in 3-5% partial melting of the mantle, or by a 15% partial melting of a granite-containing mantle with subsequent fractionation of mafic components.
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Precambrian Research, Vol. 120, Issues 3-4, 10 February, pp. 219–239. Much of the gold was deposited between 2650–2630 Ma, with much of this associated with strike-slip reactivation of earlier faults (normal and reverse). An earlier gold event 2660-2655 Ma was associated with major extension (normal faulting and granite doming) resulting in the formation of late basins and the intrusion of mantle-derived magmas (syenites and Mafic-type granites/porphyries) and tight anticlockwise PTt paths.
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The Yilgarn Craton is host to around 30% of the world's economically demonstrably recoverable reserves (EDR) of gold. Major gold deposits occur at Kalgoorlie, Kambalda, Mount Magnet, Boddington, Laverton and Wiluna, and are hosted in greenstone belts. These form linear belts of mafic, ultramafic and felsic volcanics, intercalated with sedimentary sequences, and have been deformed and metamorphosed. The mode of occurrence of the gold mineralisation tends to be small- to medium-sized structurally controlled lodes, shears, and quartz veins.
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This suggests that a more prominent structure, perhaps evidence of a prehistoric volcano, existed west of Link Lake. Also, coarsest felsic volcanic fragments occur in feldspar-phyric pyroclastic deposits exposed on the Sherman Mine property, suggesting the approximate location of a volcanic vent. Just north of the Milne Townsite lies a minor felsic volcanic vent exposed along the Milne- Sherman Road. A quartz porphyry has intruded mafic and rhyolitic lava flows and a dike of diorite.
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Saint Helena is comprised, almost universally of mafic basalts. The breccia and basalt lava flows of the Northeastern Volcanic Center formed due to undersea eruptions 14 to 11 million years ago, in the Miocene. These units were subsequently uplifted above the water surface. The Southwestern Volcanic Center covers more than half of the island and emplaced Lower Shield lava flows between 11 and 10 million years ago, followed by Main Shield flows between 11 and 9 million years ago.
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The Jacobsville Sandstone is the uppermost and youngest layer comprising about of sandstone and conglomerate that underlies Lake Superior and fills the upper part of the Lake Superior segment of the Midcontinent Rift. These sedimentary strata overlie an additional of basaltic volcanic strata and mafic intrusions that fill the remainder of the Midcontinental Rift.Cannon, W.F., Green, A.G., Hutchinson, D.R., Lee, M., Milkereit, B., Behrendt, J.C., Halls, H.C., Green, J.C., Dickas, A.B., Morey, G.B. and Sutcliffe, R., 1989.
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431x431px A number of dykes in the Okavango dyke swarm are dated as Proterozoic age (mainly ~884 Ma),Le Gall, B., G. Tshoso, F. Jourdan, G. Féraud, Hélène Bertrand, J. J. Tiercelin, A. B. Kampunzu, M. P. Modisi, J. Dyment, and M. Maia. "40 Ar/39 Ar geochronology and structural data from the giant Okavango and related mafic dyke swarms, Karoo igneous province, northern Botswana." Earth and Planetary Science Letters 202, no. 3 (2002): 595–606.
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Richterite occurs in thermally metamorphosed limestones in contact metamorphic zones. It also occurs as a hydrothermal product in mafic igneous rocks, and in manganese-rich ore deposits. Localities include Mont-Saint- Hilaire, Quebec, and Wilberforce and Tory Hill, Ontario, Canada; Långban and Pajsberg, Sweden; West Kimberley, Western Australia; Sanka, Myanmar; and, in the US, at Iron Hill, Colorado; Leucite Hills, Wyoming; and Libby, Montana. The mineral was named in 1865 for the German mineralogist Hieronymous Theodor Richter (1824–1898).
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While the mineralogy of the rock is altered throughout, texture is preserved and primary porphyry structure (including position of original veins) may still be visible. If a rock undergoes phyllic alteration, then orthoclase feldspar, biotite and various silicates are altered in addition to plagioclase. Plagioclase will be altered to sericite (a fine-grained white mica) by sericitic alteration, and mafic minerals are replaced by quartz. Tourmaline may appear as radiating aggregate or prismatic crystals between the quartz- sericite assemblage.
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The Morrissey Metamorphics are a group of metamorphic rocks dominated by pelitic and psammitic schists derived from the metamorphism of shales and sandstones. This unit also includes some metamorphosed mafic igneous rocks and carbonate rocks. The sedimentary precursors to the Morrissey Metamorphics were deposited after about 1840 Ma, and were deformed and metamorphosed at amphibolite facies during the 1830–1780 Ma Capricorn Orogeny, before being intruded by granites of the Moorarie Supersuite at 1810–1780 Ma.
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Gabbro Photomicrograph of a thin section of gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is chemically equivalent to rapid-cooling, fine-grained basalt. Much of the Earth's oceanic crust is made of gabbro, formed at mid-ocean ridges. Gabbro is also found as plutons associated with continental volcanism.
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Long belts of gabbroic intrusions are typically formed at proto-rift zones and around ancient rift zone margins, intruding into the rift flanks. Mantle plume hypotheses may rely on identifying mafic and ultramafic intrusions and coeval basalt volcanism. Nearly all gabbros are found in plutonic bodies, and the term (as the International Union of Geological Sciences recommends) is normally restricted just to plutonic rocks, although gabbro may be found as a coarse-grained interior facies of certain thick lavas.
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Consisting primarily of basaltic andesite, it has a more mafic composition than the other two volcanoes. Its deposits are rich in palagonite and red and black cinders, and they are progressively more iron-rich the younger they are. North Sister's lava flows demonstrate similar compositions throughout the mountain's long eruptive history. The oldest lava flows on North Sister have been dated to roughly 311,000 years ago, though the oldest reliably dated deposits are approximately 119,000 years old.
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The occurrence of mafic dike swarms in Archean and Paleoproterozoic terrains is often cited as evidence for mantle plume activity associated with abnormally high mantle potential temperatures. Dike swarms may extend over in width and length. The largest dike swarm known on Earth is the Mackenzie dike swarm in the western half of the Canadian Shield in Canada, which is more than wide and long. The number of known giant dike swarms on Earth is small, only about 25.
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Numerous mafic dykes intruded the basement in the late Permian and Early Jurassic, associated with the start of the separation of Africa from South America. These are part of the Central Atlantic Magmatic Province (CAMP). The northern Guiana Shield, including Guyana is separated from Southern Guiana Shield by ENE to NE trending Tumbes /Guayaquil - Tacutu Tectonic Lineament. This is a major regional pre-Cambrian shear zone / mega-shear which is believed to have been re-activated several times.
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Trachyandesite is characterized by a silica content near 58% and a total alkali oxide content near 9%. This places trachyandesite in the S3 field of the TAS diagram.. When it is possible to identify the minerals present, trachyandesite is characterized by a high content of sodic plagioclase, typically andesine, and contains at least 10% alkali feldspar. Common mafic accessory minerals are amphibole, biotite or pyroxene. Small amounts of nepheline may be present and apatite is a common accessory mineral.
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Laminations in ironstone and pelite formations suggest that the mafic volcanic rocks deposited on the low energy slope of a volcanic plateau, away from wave action. Because of the enormous time distance from the Archean, exact interpretations are less reliable. In the late Proterozoic, the region was affected by the Wopmay orogeny. Along the edge of the Archean Slave Craton, a 1.1 kilometre thick wedge of carbonates formed the Rocknest Formation, which thins to the east.
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Nuvvuagittuq Greenstone Belt (NGB) is located in the Northern Quebec, covering approximately 10 km2 of area in Hudson Bay. It resembles a north-closing synform that plunges towards the south direction. The true age of NGB is still controversial and between 4.4 Gyr year to 3.8 Gyr old. The 4.4-Gyr-old zircon in NGB does not, by its low isotopic ratio of 142-Neodymium to 144-Neodymium, represent that the mafic host rock is also of Hadean age.
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It is derived from derived from sandstones and mudstones and is composed of mica schist. Metamorphic felsic gneiss and mafic gneiss formations are common in the northern parts of the watershed. The Bryn Mawr Formation and the Bridgeton Formation are also present and are unconsolidated deposits of rock that rest on top of the dense crystalline bedrock. Mica slate is present in Marple Township and was manufactured to form "Darby Creek scythe stones" in the 1860s.
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Goat Rocks volcano as seen from Mount Adams vicinity Goat Rocks is a stratovolcano with a somewhat complicated eruptive history. It first became active approximately 3.2 million years ago during the Pliocene epoch, undergoing explosive eruptions that ejected silicic lava with highly felsic rocks like rhyolite. One of these events produced of tuff that remains, exposed, on the east flank of the existing mountain. Three million years ago Goat Rocks shifted to mafic volcanism, erupting olivine and basalt.
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Rhine Graben (blue shades) between Basel and Frankfurt with adjoining mountain ranges (green to brown); colour-coding according to digital elevation model The extension induced by the formation of the Alps was sufficient to thin the crust and provide suitable dilational conduits for magmatic and volcanic activity to occur. This resulted in the emplacement of mafic dykes, which follow the general structural trend of the extensional faults. In addition, isolated volcanoes such as the Kaiserstuhl were formed.
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The lava domes were erupted between 89,000-94,000 years ago. In Runtu Jarita, Argon-argon dating on sanidine has yielded ages of 88,000±4,000 to 97,000±2,000 BP. The eruption may have been caused by the injection of mafic magmas in the magmatic system. Presumably, the magmas were in the process of forming a pluton when the injection of new magmas led to eruption. The eruptions of Chascon initially were phreatomagmatic and influenced by local lakewaters.
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Together with mafic rocks and andesite, they are evidence of back arc environment. The late Neoproterozoic Belle-Riviere Group includes bimodal volcanic rocks such as basalt and rhyolite overlain by terrestrial sedimentary rock. Belle-Riviere Group rocks partially overlie the Tommotian Fortune Group and the early and middle Cambrian Langlade Group, which have fossiliferous limestone beds and siltstone. Discordant contact between older Precambrian rocks and Paleozoic sedimentary rocks as well as thrust faults indicate Acadian orogeny related deformation.
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Early Mississippian tuff, breccia, volcaniclastic sandstone and mafic volcanic rocks in the Skolai Group are the oldest rocks. The Skolai Group is separated from overlying Middle Triassic siltstone by a regional unconformity. Above the siltstone is the vast Nikolai Formation—basal conglomerate and basalt three kilometers thick, which extends far to the west into Alaska and as far south as Vancouver Island. It is interlayered with the Chitistone reef limestone and the deep marine McCarthy Formation.
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Recycling of existing primordial crust contributes to the production of secondary crust. Partial melting of the existing crust increases the mafic content of the melt producing basaltic secondary crust. A further method of formation due to the decay of radioactive elements within the Earth releasing heat energy and eventually causing the partial melting of upper mantle, also producing basaltic lavas. As a result, most secondary crust on Earth is formed at mid ocean ridges forming the oceanic crust.
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The Great Dyke acts as a strain-marker for the craton: The fact that it has been undeformed since intrusion (excluding the Musengezi area) shows that the craton had stabilised by the time the Dyke intruded.Dirks, P.H.G.M. and Jesma, H.A. 2002. Crust–mantle decoupling and the growth of the Archaean Zimbabwe craton. Journal of African Earth Sciences, 34, 157–166 Two mafic dykes, the East and Umvimeela, flank the Great Dyke to the east and west respectively.
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The late mafic eruption products and the Cerro Blanco volcanics are geologically classified as making up the "Purulla Supersynthem". From the Miocene to the Pliocene the La Hoyada volcanic complex was active southwest of Cerro Blanco; afterwards came a 2 million years long hiatus. Cerro Blanco overlies this volcanic complex and outcrops of La Hoyada are found inside and around the calderas. The basement is formed by metamorphic and sedimentary rocks of Paleozoic to Mesozoic age.
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Archean rocks dominate much of the territory's surface and places with overlying rock. Greenstone belts are common together with migmatite gneiss, granodiorite, and quartz monzonite, on the Melville Peninsula and northern Baffin Island, as well as the southwest mainland. Lenses and bands of amphibolite, granitoid and metasedimentary rocks are common in these areas, along with less common ultramafic rocks. Gold and other base metals are widespread as mineralization in siliclastic, felsic, mafic and ironstone rocks of the greenstone belts.
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Blue Lake Crater has a mafic composition (rich in magnesium and iron). Blue Lake Crater's major rock composition components are basalt and picrite basalt (picrobasalt). Analysis of components from Blue Lake Crater eruptive deposits for calc-alkaline melt inclusion showed compositional similarities with the Yapoah and Collier cones, indicating that Blue Lake Crater is also made up of basaltic andesite. By weight percentage, Blue Lake Crater deposits consist of about 54% Silicon dioxide (silica) and about 5% magnesium oxide.
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The tholeiitic magma series, named after the German municipality of Tholey, is one of two main magma series in igneous rocks, the other being the calc- alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma into a more evolved, silica rich end member. The International Union of Geological Sciences recommends that tholeiitic basalt be used in preference to the term "tholeiite" (Le Maitre and others, 2002).
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These dark beds lack any spectral signatures of common mafic minerals such as pyroxenes, olivine, or iron oxides (like hematite). Against fluted terrains the beds have been observed to dip between 15° and 25°. These thick and friable units, at their greatest extents, reach up to in thickness. They are capped by a highly resistant unit interpreted by some researchers to be volcanic in origin, but which has been undermined by the erosion of the underlying weak rock.
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Bornite is an important copper ore mineral and occurs widely in porphyry copper deposits along with the more common chalcopyrite. Chalcopyrite and bornite are both typically replaced by chalcocite and covellite in the supergene enrichment zone of copper deposits. Bornite is also found as disseminations in mafic igneous rocks, in contact metamorphic skarn deposits, in pegmatites and in sedimentary cupriferous shales. It is important as an ore for its copper content of about 63 percent by mass.
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Amphibolite need not be derived from metamorphosed mafic rocks. Because metamorphism creates minerals entirely based upon the chemistry of the protolith, certain 'dirty marls' and volcanic sediments may actually metamorphose to an amphibolite assemblage. Deposits containing dolomite and siderite also readily yield amphibolite (tremolite-schist, grunerite-schist, and others) especially where there has been a certain amount of contact metamorphism by adjacent granitic masses. Metamorphosed basalt creates ortho-amphibolite and other chemically appropriate lithologies create para-amphibolite.
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Tuttle and Bowen accomplished their work by using experimental petrologic laboratories that produce synthetic igneous materials from mixes of reagents. Observations from these experiments indicate that as a melt cools, it will produce derivative magmas and igneous rock. Following Bowen's research, the magma will crystallize a mafic igneous rock prior to a felsic igneous rock. As this crystallization process occurs in nature, pressure and temperature decrease, which changes the composition of the melt along various stages of the process.
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A decrease in temperature and confining pressure will allow an increase in crystallization and vapor pressure of the dissolved gas. Depending on the composition of the melt, this ascent can be either slow or fast. Felsic magmas are very viscous and travel to the surface of the Earth slower than mafic melts whose silica levels are lower. The amount of gas available to be exsolved and the concentrations of gases in the melt also control ascension of the magma.
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The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows are uncommon, but have travelled as far as . Stratovolcanoes are sometimes called "composite volcanoes" because of their composite stratified structure built up from sequential outpourings of erupted materials. They are among the most common types of volcanoes, in contrast to the less common shield volcanoes.
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Optical microscope photograph; the length of the crystal is about 250 µm Zircon is common in the crust of Earth. It occurs as a common accessory mineral in igneous rocks (as primary crystallization products), in metamorphic rocks and as detrital grains in sedimentary rocks. Large zircon crystals are rare. Their average size in granite rocks is about 0.1–0.3 mm, but they can also grow to sizes of several centimeters, especially in mafic pegmatites and carbonatites.
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The gorge was carved approximately 13,000 years ago as the Laurentide Ice Sheet retreated across the region. The carving is thought to be a result of rapid downcutting of the Ottauquechee River after the drainage of glacial Lake Hitchcock. The gorge cuts through bedrock of the Devonian Gile Mountain Formation and Mesozoic mafic dikes can be seen on the west wall.McHone, Gregory, 1981, The origin of the Quechee Gorge: Green Mountain Geologist, Vt Geological Society, Fall 1981, Vol.
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The refractive index ranges from 1.559 to 1.573 and twinning is common. As with all plagioclase members, the crystal system is triclinic, and three directions of cleavage are present, two of which are nearly at right angles and are more obvious, being of good to perfect quality. (The third direction is poor.) It occurs as clear, white to gray, blocky to lath shaped grains in common mafic igneous rocks such as basalt and gabbro, as well as in anorthosites.
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Io consists of a continuous stack of mafic and ultramafic deposits. After new erupted volcanic materials cool down and are buried, the stack of rocks become indurated and form bedrocks. The bedrocks are fractured due to tidal flexing, compression at depth, volcanic intrusion and other mechanisms, and then are broken into large blocks a hundred kilometers across. Products of magmatism like sills, dikes and batholiths may intrude into layers of stacking volcanics to form a composite crust.
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The Jack Hills are located in the Narryer Gneiss Terrane of the Yilgarn Craton, Western Australia, and comprise an long northeast-trending belt of folded and metamorphosed supracrustal rocks. Sedimentary siliciclastic rocks, interpreted as alluvial fan-delta deposits, are the major lithology. Minor mafic/ultramafic rocks and banded iron formation (BIF) are also found in the sequence. The overall sequence is generally considered to be a granulite gneiss, which has undergone multiple deformations and multiple metamorphic episodes.
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On the other hand, those in Qixia Complex only record the younger metamorphisms. This suggests the record of the metamorphism 2.65 billion years ago was removed and overprinted by later metamorphic events. On top of that, the formation of greenstone and gneiss in Luxi and Qixia are considered to be linked to a wider geological event, the Large Igneous Province event 2.7 billion years ago. Magma was extracted and led to the formation of a mafic crust.
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These are typically greenish in colour and composed of clinopyroxene, altered to hornblende and plagioclase, and are regarded as the earliest phase of the Complex. The Complex includes layered mafic intrusions (the Rustenburg Layered Suite) and a felsic phase. The complex has its geographic centre located north of Pretoria in South Africa at about 25° S and 29° E. It covers over , an area the size of Ireland. The complex varies in thickness, in places reaching thick.
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Each of these are in a syncline and are surrounded by Silurian metamorphic rocks with an inward-dipping thrust zone forming the boundary. The kinds of rock in the mafic massifs are schists, gneiss, amphibolite, metagabbro, granulite, eclogite, and serpentine. The Ordes Massif dates from 380 to 390 Ma, and represents part of the Rheno-Hercynian Ocean as part of an accretionary wedge. It became joined to the European Hunic Terrane between the Channel Block and the allochthenous nappe.
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In igneous petrology the term more specifically refers to the volatile components of magma (mostly water vapor and carbon dioxide) that affect the appearance and explosivity of volcanoes. Volatiles in a magma with a high viscosity, generally felsic with a higher silica (SiO2) content, tend to produce eruptions that are explosive. Volatiles in a magma with a low viscosity, generally mafic with a lower silica content, tend to vent and can give rise to a lava fountain.
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West doorway at St Germans Church; built of Tartan Down stone (Landrake)Beacham, Peter & Pevsner, Nikolaus (2014) Cornwall. (The Buildings of England.) New Haven: Yale University Press; p. 543 A simplified map showing the granite batholiths and mafic igneous rocks of Cornwall Elvan is a name used in Cornwall and Devon for the native varieties of quartz-porphyry. They are dispersed irregularly in the Upper Devonian series of rocks and some of them make very fine building stones (e.g.
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A substitution of the element aluminium can also occur, leading to hercynite (FeAl2O4). Chromite today is mined particularly to make stainless steel through the production of ferrochrome (FeCr), which is an iron-chromium alloy. Chromite grains are commonly found in large mafic igneous intrusions such as the Bushveld in South Africa and India. Chromite is iron-black in color with a metallic luster, a dark brown streak and a hardness on the Mohs scale of 5.5.
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Minette (a type of lamprophyre), from Jáchymov in the Czech Republic Lamprophyres (Greek λαμπρός (lamprós) = "bright" and φύρω (phýro) = to mix) are uncommon, small volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks and small intrusions. They are alkaline silica-undersaturated mafic or ultramafic rocks with high magnesium oxide, >3% potassium oxide, high sodium oxide and high nickel and chromium. Lamprophyres occur throughout all geologic eras. Archaean examples are commonly associated with lode gold deposits.
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Volcanogenic massive sulfide deposits form when mafic magma at depth, (perhaps a few kilometers beneath the surface), acts as a heat source, causing convective circulation of seawater through the oceanic crust. The hydrothermal fluid leaches metals as it descends and precipitates minerals as it rises. Sedimentary exhalative deposits, also called sedex deposits, are lead-zinc sulfide deposits formed in intracratonic sedimentary basins by the submarine venting of hydrothermal fluids. These deposits are typically hosted in shale.
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Confirmed by geochemical modelling, TTG type magma can be generated through partial melting of hydrated meta-mafic rocks. To produce the very low HREE pattern, the melting should be conducted under a garnet-stable pressure-temperature field. Given that garnet temperature stability rises dramatically with increasing pressure, strongly HREE-depleted TTG melts are expected to form under relatively high pressure. Besides the source composition and the pressure, the degree of melting and temperature also influence the melt composition.
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102-104 Radiometric dates of 1883-1870 Ma are reported for mafic, ultramafic, carbonatite and lamprophyre intrusions within the Trough. It is a large iron ore belt developed on banded iron formations and has had mining operations since 1954.Iron Deposits of the Labrador Trough At least two large magmatic events occurred in the Labrador Trough. The first event 2,170 million years ago engulfed an area of and the second 1,880 million years ago covered a similar area of .
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Oroscocha is formed by phenocryst-rich, felsic porphyritic rocks with a composition of peraluminous rhyolite in the flows and trachydacite in the dome, of which the dome is darker than the lava flows. Mafic inclusions with sizes larger in the lava flows than in the dome are also found. The magma that gave rise to the rocks was probably modified by the injection of lamprophyres while still in the magma chamber. Quimsachata is formed by -rich andesite.
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The metasedimentary rocks are quartz-rich and the amphibolites represent mafic igneous intrusions. Age analyses of detrital minerals, petrology, and geochemistry all indicate that the island belongs geologically with the other islands of the Outer Banda Arc. This series of islands formed when the northern edge of the Australian continent was upthrust in collision with southeast Asia. These islands are paralleled by the Inner Banda Arc, a series of active and extinct volcanic islands, including neighboring Wetar.
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Finally, the mixing of magma chamber contents with new and more mafic magma shortly before each eruption played an important role in rock genesis. In the case of Lastarria, this mixing occurs in a stratified magma chamber, with active convection occurring between lighter and colder upper contents and hotter and denser lower contents. A number of alteration products are also present, some of which have been visualized by aerial imagery. Fumarole deposits contain encrustations and sublimates.
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The summit of Jabal Maqlā consists mainly of dark-colored hornfels derived from metamorphosed volcanic rocks that originally were silicic and mafic lava flows, tuff breccias, and fragmental greenstones. The middle and lower slopes of Jabal Maqlā consist of light- colored granite, which has intruded into the overlying hornfels. This is the same granite that comprises Jabal al-Lawz.Trent, V.A., and R.F. Johnson (1967) Geologic map of the Jabal al Lawz Quadrangle, Kingdom of Saudi Arabia; 1:100,000.
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The pre- caldera lava domes were generated either directly from a common magma chamber or indirectly through secondary chambers. The lead isotope ratios are consistent with the volcano having formed at the edge of an area of granite and rhyolite of Paleozoic age. Incapillo magmas probably formed as adakitic high-pressure mafic magmas derived from the crust, either directly by anatexis or indirectly by dragged-down crustal fragments. The magmas are then modified by crustal contamination and fractional crystallization.
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Contrary to rumors, Pinnacle Mountain is not a volcano. Despite its resemblance to a cinder cone, Pinnacle Mountain is composed of deep-water sedimentary rock, the Pennsylvanian Jackfork Sandstone. Named for Jackfork Mountain in Pittsburg and Pushmataha counties, Oklahoma, the Jackfork Sandstone at Pinnacle Mountain is massive, fine- to coarse-grained, mostly tan quartzitic sandstone of great hardness. Cinder cones, on the other hand, form from the eruption of mafic lavas and are composed of extrusive igneous rocks such as basalt.
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The geology of Guam formed as a result of mafic, felsic and intermediate composition volcanic rocks erupting below the ocean, building up the base of the island in the Eocene, between 33.9 and 56 million years ago. The island emerged above the water in the Eocene, although the volcanic crater collapsed. A second volcanic crater formed on the south of the island in the Oligocene and Miocene. In the shallow water, numerous limestone formations took shape, with thick alternating layers of volcanic material.
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The Nazca Plate subducts beneath the South America Plate, giving rise to the volcanism in the Andean Central Volcanic Zone, including mafic back-arc volcanism which is often associated with tectonic lineaments. Los Gemelos () and El Saladillo () lie in the Calchaqui Valley, close to the towns of La Poma and El Saladillo. The valley is bordered by two thrust faults, at least one (the Calchaqui fault) of which has had historical earthquakes; the Los Gemelos volcanic cones were constructed along the fault.
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The northern segment consists of one large volcanic complex, the Mount Meager massif, and a group of basaltic and andesitic volcanoes known as the Bridge River Cones. Mount Meager is composed of at least four overlapping stratovolcanoes that become progressively younger from south to north. These were formed in the last 2.2 million years, with the latest eruption having been about 2,350 years ago. The mafic, intermediate and felsic volcanic rocks comprising Meager were erupted from at least eight volcanic vents.
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Most of the dykes are basaltic in composition but a minority are trachytic. The dominant trend of the dykes is northwest-southeast although they are locally in part radial near the old volcanic centre. On the Trotternish peninsula, mafic magma was intruded along the bedding planes of the Jurassic sedimentary rocks beneath the lavas to form sills that are up to 90m thick. They commonly display columnar jointing, such as in the upper part of the Kilt Rock at Staffin.
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Oxygen and silicon are by far the two most important – oxygen composes 47% of the crust by weight, and silicon accounts for 28%., pp. 4–7 The minerals that form are directly controlled by the bulk chemistry of the parent body. For example, a magma rich in iron and magnesium will form mafic minerals, such as olivine and the pyroxenes; in contrast, a more silica-rich magma will crystallize to form minerals that incorporate more SiO2, such as the feldspars and quartz.
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Drosera ultramafica is a species of sundew native to the highlands of Malesia. It is thought to be most closely related to Drosera spatulata, Drosera neocaledonica and Drosera oblanceolata. The taxon is readily distinguished from the former by its general habit and preference for mafic, upland habitats, and from the latter species by specific morphological differences, in addition to the fact that their geographical ranges do not overlap.Fleischmann, A., A.S. Robinson, S. McPherson, V. Heinrich, E. Gironella & D.A. Madulid 2011.
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This southwards migration results in a steepening of the subducting plate behind the ridge, causing decompression melting. Between 1:4 to 1:6 of the generated melts are erupted to the surface as ignimbrites. Mafic rocks are associated with strike-slip faults and normal faults and are found in the southern Puna and Altiplano. The southern Puna has calc-alkaline andesites erupted after 7 mya, with the least evolved magmas being the 6.7 mya Cerro Morado and 8–7 m Rachaite complex flows.
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Like enstatite, bronzite is a constituent of many mafic to ultramafic igneous rocks, such as, norite, gabbro, and especially peridotite, and of the serpentinites which have been derived from them. It also occurs in some crystalline schist. Bronzitite, a pyroxenite of bronzite composition, is noted in the cumulate rocks of the Stillwater igneous complex of Montana.Jackson, Everett D., The Chromite Deposits of the Stillwater Complex, Montana in Ore Deposites of the Unitrd States, 1933-1967 (The Graton-Sales Volume) Vol.
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In many mafic igneous rocks, such as gabbro and diabase, scapolite replaces feldspar by a secondary or metasomatic process. Some Norwegian scapolite-gabbros (or diorite) examined microscopically furnish examples of every stage of the process. The chemical changes involved are really small, one of the most important being the assumption of a small amount of chlorine in the new molecule. Often the scapolite is seen spreading through the feldspar, portions being completely replaced, while others are still fresh and unaltered.
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The middle rock assemblage consists of a series of metamorphosed volcanic rocks with compositions varying from acidic to mafic. The top layer is made by meta- sedimentary rocks, for example quartzite and marble. According to the data of zircon dating, the bottom layer of the greenstone sequence formed in about 2.54 billion years ago, while the middle and upper layers have the age later than 2.51 billion years. Granitoids are intrusive igneous rocks that primarily made by quartz, feldspars and micas.
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The outcropping geology comprises an area of mafic to intermediate volcanics that form a large easterly trending range of hills in the northern portion of the property. This range is dominated by a prominent and strongly magnetic BIF extending for at least 8 km across the property. Smaller BIF units occur elsewhere within the volcanic succession and these are typically 5 to 10m wide representing thin interflow sediments to the volcanics. The greenstones are most likely part of the Upper Nyanzian System.
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This includes slab windows, mantle plumes, crustal extension and deglaciation. The most common and best mechanism used to explain NCVP volcanic activity is incipient rifting of the North American Plate caused by crustal extension. As the continental crust stretches, the near surface rocks fracture along steeply dipping cracks parallel to the rift known as faults. Mafic magma rises along these fractures to create fluid lava flows, although more viscous felsic magma also makes its way to the surface and can produce explosive eruptions.
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The oldest part of the Lewisian complex is a group of gneisses of Archaean age that formed in the interval 3.0-2.7 Ga. These gneisses are found throughout the outcrop of the Lewisian complex in the mainland. The dominant lithology of the Scourie complex is banded grey gneisses, typically granodioritic, tonalitic or trondhjemitic in composition. Metasedimentary gneisses are relatively rare. The protolith for the Scourian gneisses are thought to be granitic, with subsidiary mafic and ultramafic plutonic rocks giving an overall bimodal character.
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The rift began as a hot spot of basaltic magma underneath the Lake Superior region; it extruded layers of lava up to thick and extending up to on either side of the rift. The deposited lava along the North Shore of Lake Superior is thick. This was a fast-spreading rift; the resulting basalts show little interaction with the then-existing rock. These immense volumes of mafic lava were generated in two major pulses, mostly via a hot mantle plume.
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The lava flows missed, sometimes by mere yards, the Mother Temple of Besakih. The saving of the temple is regarded by Balinese as miraculous and a signal from the gods that they wished to demonstrate their power but not destroy the monument that the Balinese had erected. Andesite was the dominant lava type with some samples mafic enough to be classified as basaltic andesite.Self, S., and M.R. Rampino, 2012: The 1963–1964 eruption of Agung volcano (Bali, Indonesia). Bull. Vulcanol.
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Qal'eh Hasan Ali is part of a large orogenic province that was formed by the closures of the Paleotethys, Neotethys and the Sistan oceans as well as by ongoing subduction off the Makran area. The resulting collision of terranes and continents has formed the Iranian high plateau. Volcanic activity in the region of the Lut commenced during the Jurassic and reached a peak at the end of the Eocene. After the Eocene, calc-alkaline volcanism diminished and mafic volcanism became dominant.
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Cerro Chascon-Runtu Jarita is a complex of lava domes located inside, but probably unrelated to, the Pastos Grandes caldera. It is part of the more recent phase of activity of the Altiplano-Puna volcanic complex. Accompanied with little explosive activity on the main dome Cerro Chascon, it contains ten lava domes arranged in a chain. Located in the floor of the Pastos Grandes caldera, these domes were erupted after injection of mafic magmas in the deep less than 100,000 years ago.
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Volcanism of the Chukotat Group might have originated from rifting of a microcontinent that now forms the southwestern portion of Baffin Island. Map showing the age of geologic features related to the Circum-Superior Belt. Geologic features include: 1 = Carbonatite feeder, 2 = Montagnais gabbro sills, 3 = rhyodacite, 4 = Chukotat volcanics, 5 = Belcher and Sleeper Island sills, 6 = Fox River sill, 7 = Molsen dikes, 8 = Thompson belt mafic-untramafic magmatism, 9 = Winnipegosis komatiite, 10 = Hemlock formation, 11 = Gunflint formation, 12 = Pickle Crow dike.
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Bedrock around the southern two-thirds of the lake is meta-igneous rock of Lower Paleozoic age which is rich in mafic minerals except along southeastern shores where felsic minerals dominate. Bands of marble up to several meters thick are scattered within this metamorphic complex. Around northern shores are volcanic rocks of variable composition from the Jurassic period. Soils around the lake are mostly well drained or rapidly drained gravelly sandy loams or gravelly loamy sands with brown podzolic profile development.
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To this it adds the large nepheline syenite bodies of the Lovozero Massif and the Khibiny Mountains. An estimate puts the total volume of the rocks of the Kola Alkaline Province at 15,000 ±2,700 km3. The more mafic silicate rocks of the province originated from small degrees of partial melting in a source region in Earth's mantle made up of garnet-bearing peridotite. The lithosphere had thicknesses similar to present-day (200 km) conditions when magmas originated in the Devonian.
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The sedimentary rocks of the basin are extensively intruded by igneous plugs, dikes and sills of Eocene to Oligocene age. Two large granitic intrusives near the axis of the basin form East Spanish Peak and West Spanish Peak. Dikes of felsic to intermediate composition radiate outward from East and West Spanish Peaks, and on the north side of the peaks have the appearance of large stone walls. Dikes of mafic and ultramafic composition trend east-northeast to west-southwest across the basin.
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Pilot Knob is one of around 75 late-Cretaceous Period volcanic complexes scattered around Central Texas from Waco to Austin, San Antonio, and Del Rio. All of these volcanoes have been extinct for millions of years. The Pilot Knob volcanic complex consists of four small, rounded hills (including Pilot Knob proper) forming the volcano's core area in an area two miles in diameter. The hills are composed of trap rock which is an erosion-resistant, fine-grained mafic volcanic rock.
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The Pampean orogen contains a magmatic belt including granodiorites, monzogranites, and volcanic rocks, all of them of calc-alkaline chemistry. The igneous rocks of this belt formed at various times in over the period from 555 to 525 million years ago. From 525 million years ago onward another magmatic belt of peralumineous and mafic rocks developed further amidst gneiss, schist, amphibolites and carbonate rocks. The igneous rocks of this belt formed in the period from 525 to 515 million years ago.
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Vegetation change from the Dun Mountain Ophiolite Belt ultramafic rock (left) to mafic and sedimentary rock on the right. The Dun Mountain Ophiolite Belt is a locally intact approximately section through oceanic crust. It is exposed between D'Urville Island in Marlborough District and St Arnaud in Tasman District, and Jackson Bay in the West Coast Region and Balclutha in Otago. The Dun Mountain Ophiolite Belt is exposed in the South Island and is inferred to exist at depth under the North Island.
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Andesitic magma is composed of many gases and melted mantle rocks. Cinder or scoria cones violently expel lava with high gas content, and due to the vapor bubbles in this mafic lava, the extrusive basalt scoria is formed. Lava domes are formed by high viscosity lava that piles up, forming a dome shape. Domes typically solidify to form the rich in silica extrusive rock obsidian and sometimes dacite domes form the extrusive rock dacite, like in the case of Mount St. Helens.
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Haggertyite is a rare barium, iron, magnesium, titanate mineral: Ba(Fe2+6Ti5Mg)O19 first described in 1996 from the Crater of Diamonds State Park near Murfreesboro in Pike County, Arkansas. The microscopic metallic mineral crystallizes in the hexagonal system and forms tiny hexagonal plates associated with richterite and serpentinitized olivine of mafic xenoliths in the lamproite host rock. It is an iron(II) rich member of the magnetoplumbite group. It is a light grey opaque mineral with calculated Mohs hardness of 5.
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Dark gray to light gray in color, Boring Lava produces columnar and platy joints, which can be seen in Oregon east of Portland and in Clark County in Washington state. It is usually phyric, though one sample from Rocky Butte consists of labradorite with olivine phenocrysts that have been transformed to iddingsite. The Boring Lava reaches thicknesses of more than . Boring Lava has a more mafic (rich in magnesium in iron) composition than the nearby volcano Mount Hood, but they have similar ages.
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The Chonide orogeny was a mountain building event in the Triassic, preserved in coastal accretionary complexes in southwestern Chile. The Chonos Metamorphic Complex, Madre de Dios Accretionary Complex and Diego de Almagro Complex all crop out west of the South Patagonian Batholith. Rocks in the Chonos Metamorphic Complex include turbidites as well as meta-chert and mafic schist. Some researchers propose that during the Permian, the supercontinent Gondwana moved rapidly northward leading to the formation of back-arc marginal basins.
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New South Wales Department of Mineral Resources, Sydney. Its heat changed the nature of the surrounding rock to produce a variety of minerals, predominantly coarse grained picrite with olivine-dolerite. The picrite is a coarse-grained rock henpecked by olivine and is made up of two-thirds of the lower component of the intrusion, with the upper third of dolerite also containing other mafic minerals. It didn't quite reach the surface but pushed the surface rocks upwards to form a dome.
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Diopside crystal from De Kalb, New York (size: 4.3 x 3.3 x 1.9 cm) Diopside is found in ultramafic (kimberlite and peridotite) igneous rocks, and diopside-rich augite is common in mafic rocks, such as olivine basalt and andesite. Diopside is also found in a variety of metamorphic rocks, such as in contact metamorphosed skarns developed from high silica dolomites. It is an important mineral in the Earth's mantle and is common in peridotite xenoliths erupted in kimberlite and alkali basalt.
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Two types of lava are named according to the surface texture: Aa (pronounced ) and pāhoehoe (), both Hawaiian words. Aa is characterized by a rough, clinkery surface and is the typical texture of viscous lava flows. However, even basaltic or mafic flows can be erupted as aa flows, particularly if the eruption rate is high and the slope is steep. Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows.
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Cinder Cone is in Lassen Volcanic National Park. Cinder Cone is a -high volcanic cone of loose scoria. The youngest mafic volcano in the Lassen volcanic center, it is surrounded by unvegetated block lava and has concentric craters at its summit, which have diameters of and . Cinder Cone comprises five basaltic andesite and andesite lava flows, and it also has two cinder cone volcanoes, with two scoria cones, the first of which was mostly destroyed by lava flows from its base.
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The Long Range dikes are a Neoproterozoic mafic dike swarm of Newfoundland and Labrador, Canada. It consists of a large igneous province with an area of that was constructed about 620 million years ago when Laurentia broke-up from Baltica. Its formation might have occurred when the ancient Iapetus Ocean began to open. Long Range is the oldest of a series of magmatic events that occurred along the eastern margin of Laurentia 620–560 Ma, before the opening of the Iapetus Ocean.
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The vast Bushveld Igneous Complex of South Africa is a large layered mafic to ultramafic igneous body with some layers consisting of 90% chromite making the rare rock type, chromitite.Guilbert, John M., and Park, Charles F., Jr. (1986) The Geology of Ore Deposits, Freeman, The Stillwater Igneous Complex in Montana also contains significant chromite. Chromite is found in large quantities that is available for commercial mining. The chromite minerals are found in 2 main deposits, which are stratiform deposits and podiform deposits.
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North of Pinhead Buttes, the volcanoes in this region are older and less tall, usually between in elevation. South of Pinhead Buttes, the Cascades becomes younger Pleistocene volcanoes, which often have glaciers. Mount Jefferson may form part of a long- lasting intracrustal melting and magma storage area that encompasses an area of , where relatively little mafic eruptive activity has occurred. The melting of the metamorphic rocks amphibolite and at deeper strata, granulite, have both produced intermediate and silicic lavas at Jefferson.
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Litchfieldite (nepheline syenite gneiss) from Canaã Massif, Brazil Litchfieldite is a rare igneous rock. It is a coarse-grained, foliated variety of nepheline syenite,Le Maitre, R.W. (2002) Igneous Rocks - A Classification and Glossary of Terms, 2nd edition, Cambridge, Cambridge University Press, page 105. sometimes called nepheline syenite gneiss or gneissic nepeheline syenite.Robins, B. and Tysseland, M. (1979) Fenitization of some mafic igneous rocks in the Seiland province, northern Norway , Norsk Geologisk Tidsskrift, Volume 59 Number 1 pages 1-23, page 3.
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When magma cools it begins to form solid mineral phases. Some of these settle at the bottom of the magma chamber forming cumulates that might form mafic layered intrusions. Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as gabbro, diorite and granite, depending upon the composition of the magma. Alternatively, if the magma is erupted it forms volcanic rocks such as basalt, andesite and rhyolite (the extrusive equivalents of gabbro, diorite and granite, respectively).
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Cerro Bitiche is part of a number of mafic volcanic centres associated with the Altiplano-Puna volcanic complex. The two major calderas La Pacana and Cerro Guacha are close to Cerro Bitiche, the eastern margin of Guacha's oldest caldera is located just east of Bitiche. Ordovician marine sequences form the tectonic basement of the area, but most of it is covered by ignimbrites and lavas between 8.5-4 million years old. The volcanic field covers a surface area of , including lava flows and scoria cones.
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Chromitite layers occur commonly in large mafic layered intrusions. A current theory suggests chromitites form as a result of introduction and mixing of chemically primitive magma with a more evolved magma, which results in supersaturation of chromite in the mixture and the formation of a nearly monomineralic layer on the magma chamber floor. The leading theory regarding the formation of the Merensky reef is that of crystals originating from a main magma source accumulated and cooled as the magma rose resulting in crystallization.Mathez, E,A. (1995).
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The TGB, at 2.7 billion years old, dates back to the formation of the supercontinent Kenorland between 2.8 and 2.6 billion years ago. This large landmass consisted of the Baltic and Siberian shields of Eurasia and Archean provinces of North America, including the Superior craton of which the Temagami belt occupies a part. Rifting of Kenorland began 2.45 billion years ago in Ontario with the formation of several large igneous provinces. Initial rifting is represented by basal mafic volcanic rocks in the nearby Huronian Supergroup.
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Natural ore deposits are located in synclines and up against mafic dikes. Beneficiation commenced in 1954 and this concentration of iron into pellets accounted for 73 percent of production by 1965. Early mining used open-pit mining methods, but was replaced with underground mining by 1880. The Marquette Iron Range was discovered in 1844 by a party of surveyors led by William A. Burt, who found that their sensitive magnetic compasses produced skewed results because of the concentration of iron in the land they were surveying.
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Olivine, of which peridot is a type, is a common mineral in mafic and ultramafic rocks, often found in lava and in peridotite xenoliths of the mantle, which lava carries to the surface; however, gem-quality peridot occurs in only a fraction of these settings. Peridots can also be found in meteorites. Peridots can be differentiated by size and composition. A peridot formed as a result of volcanic activity tends to contain higher concentrations of lithium, nickel and zinc than those found in meteorites.
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Extending north of the Mount Meager massif almost to the Interior Plateau are the Bridge River Cones. This group of small volcanoes on the upper Bridge River includes stratovolcanoes, volcanic plugs and lava flows. These volcanoes are unlike others throughout the Garibaldi Belt in that they are mainly composed of volcanic rocks with mafic compositions, including alkaline basalt and hawaiite. The different magma compositions might be related to a smaller degree of partial melting in the Earth's mantle or a descending plate edge effect.
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The Ganguan Greenstone Belt is 3.2 billion years old and contains sericite quartzites, quartz phyllite, talc schist poor in quartz and chlorite schist. The Kibalian Greenstone Belt appears at surface level to be separate belts, divided up by the Upper Congo Granitoid Massif, but geologists believe it is actually a continuous greenstone belt with mafic and intermediate volcanic rocks in the west and banded iron formations in the east. Granitoid rocks are the most common in northeastern DRC, probably formed from monzonite granites and tonalities.
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Viola subsinuata, commonly called the early blue violet,Viola subsinuata at New England Wildflower Society is a species of flowering plant in the violet family (Violaceae). It is native to eastern North America, where it is primarily found in the Appalachian Mountains and Great Lakes area. Its natural habitat is in loamy forests, often over mafic or calcareous substrates. A Systematic Revision of the Viola pedatifida Group and Evidence for the Recognition of Viola virginiana, a New Narrow Endemic of the Virginia Shale Barrens, by Bethany Zumwalde.
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Carbonate rocks are rare, indicating that the oceans were more acidic due to dissolved carbon dioxide than during the Proterozoic. Greenstone belts are typical Archean formations, consisting of alternating units of metamorphosed mafic igneous and sedimentary rocks, including Archean felsic volcanic rocks. The metamorphosed igneous rocks were derived from volcanic island arcs, while the metamorphosed sediments represent deep-sea sediments eroded from the neighboring island arcs and deposited in a forearc basin. Greenstone belts, being both types of metamorphosed rock, represent sutures between the protocontinents.
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Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle (peridotite) and is denser than continental lithosphere, for which the mantle is associated with crust made of felsic rocks. Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes the oceanic lithosphere to become increasingly thick and dense with age. In fact, oceanic lithosphere is a thermal boundary layer for the convectionDonald L. Turcotte, Gerald Schubert, Geodynamics.
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Rocks produced by the Karoo triple junction are predominantly continental flood basalts, which are usually associated with huge magmatic events during the Phanerozoic eon. In the Karoo triple junction, rocks are dated to the 180 Ma Karoo magmatic event, which occurred due to the breakup of Gondwana and the opening of Indian Ocean. It consisted of mafic lava flow, dykes, and sills covering a paleo-surface of 3 × 106 km2. Jurassic dykes found in the dyke swarms are mostly composed of dolerite, containing clinopyroxene, plagioclase, and olivine.
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Granite is a natural source of radiation, like most natural stones. Potassium-40 is a radioactive isotope of weak emission, and a constituent of alkali feldspar, which in turn is a common component of granitic rocks, more abundant in alkali feldspar granite and syenites. Some granites contain around 10 to 20 parts per million (ppm) of uranium. By contrast, more mafic rocks, such as tonalite, gabbro and diorite, have 1 to 5 ppm uranium, and limestones and sedimentary rocks usually have equally low amounts.
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Mars Odyssey Launched in 2001, although it carried multiple instruments only Thermal Emission Imaging System was designed to look at minerals. This allowed it to detect the presence of quartz, olivine, and hematite. Mars Express Launched in 2003 the Visible and Infrared Mineralogical Mapping Spectrometer (OMEGA) observed montmorillonite and localized phyllosilicate minerals. Mars Reconnaissance Orbiter Launched in 2005 this orbiter carried multiple instruments which found the mineralogy to be dominated by mafic minerals such as olivine, mica, pyroxene and smectite clays such as kaolinite.
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Mixing processes involving hotter or more mafic magmas played a role in the genesis of Uturuncu rocks, as did fractional crystallization processes and contamination with crustal rocks. The origin of these magmas appears to relate to the Altiplano-Puna magmatic body, which generates melts through differentiation of basaltic magmas first to andesites and then to dacites before being transferred to the shallow crust below Uturuncu from where it was then erupted through buoyancy-dependent processes. Magma composition has been stable over the history of the volcano.
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While many oceanic plateaus are composed of continental crust, and often form a step interrupting the continental slope, some plateaus are undersea remnants of large igneous provinces. Continental crust has the highest amount of silicon (such rock is called felsic). Oceanic crust has a smaller amount of silicon (mafic rock). The anomalous volcanism associated with the formation of oceanic plateaux at the time of the Cenomanian-Turonian boundary (90.4 million years) ago may have been responsible for the environmental disturbances that occurred at that time.
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These zones are identified by typical seismic velocities between 7.2-7.7 km/s and are usually interpreted as layers of mafic to ultramafic rocks that have underplated the transitional crust. Asthenospheric upwelling leads to the formation of a mid-ocean ridge and new oceanic crust progressively separates the once-conjoined rift halves. Continued volcanic eruptions spread lava flows across transitional crust and onto oceanic crust. Due to the high rate of magmatic activity the new oceanic crust forms much thicker than typical oceanic crust.
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Goat Rocks is an extinct stratovolcano in the Cascade Range, located between Mount Rainier and Mount Adams in southern Washington, in the United States. Part of the Cascade Volcanoes, it was formed by the subduction of the Juan de Fuca Plate under the western edge of the North American Plate. The volcano was active from 3.2 million years ago until eruptions ceased between 1 and 0.5 million years ago. Throughout its complex eruptive history, volcanism shifted from silicic explosive eruptions to voluminous, mafic activity.
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Lake Turkana is an East African Rift feature.A good introduction is stated in the Regions of Kenya site. A rift is a weak place in the Earth's crust due to the separation of two tectonic plates, often accompanied by a graben, or trough, in which lake water can collect. The rift began when East Africa, impelled by currents in the mantle,For the mantle currents, or "plumes", see the abstract of Tertiary Mafic Lavas of Turkana ..., Journal of Petrology Volume 47, Number 6 Pp. 1221–1244.
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Lava flows contain andesite and dacite of relatively uniform composition, the former containing amphibole. The morphology of the two long lava flows from Volcan Paruma implies that they were formed by lavas more mafic than is typical for the region, perhaps by andesite-andesite. Fumarolic alteration is widespread on the volcanic complex, being conspicuous on the ridge between Olca and Volcan Paruma and on the northern and southeastern flanks. Sulfur is present on the volcano, mainly around Olca, and was mined into the 1980s.
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When the Sun is at a high angle, the rim and central mountains appear brighter than the surroundings, and white patches can be viewed on the crater floor. Infrared studies of the crater region have revealed at least three layers of strata. The impact may also have intersected a mafic pluton, which means a crystallized body of igneous rock that has high concentrations of heavier elements (such as magnesium, in this case). Two smaller but notable craters lie just to the south of the main crater.
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The long Labrador Trough, extending from Ungava Bay through Quebec and Labrador, includes two volcano- sedimentary series, the first ranging from 2,170 to 2,140 million years old and second ranging from 1,883 to 1,870 million years old. This magmatism is considered to have formed as a result of back-arc volcanism. The youngest magmatic series (1883-1870 Ma) contains 1,880 million-year-old carbonatites and lamprophyres. 1,883 to 1,874 million-year-old mafic and a few ultramafic magmas comprise the Willbob and Hellancourt formations and Montagnais sills.
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Nickel, copper and platinum group elements formed in ultramafic intrusions within the Nikolai Formation, deposited as gabbro, pyroxenite and dunite as the Kluane mafic-ultramafic complex. During the Triassic, rifting may have briefly separated the two terrains before they rejoined, a possibility inferred from the Duke River Fault "suture" between the two terranes. The two terranes have overlap assemblages with rocks formed across the two landmasses. The thick Dezadesh Formation turbidite and tuff deposited in a basin from the late Jurassic into the early Cretaceous.
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The oldest rocks in North Carolina are part of the Grenville Province, which stretches from Texas to Labrador and which was impacted by the Grenville orogeny in the Mesoproterozoic to form the Appalachian Mountains. Grenville age rocks are exposed in the Blue Ridge province and the Sauratown Mountains. The Bakersville mafic dike swarm from 734 million years ago along with the peralkaline granites of the Crossnore Complex and bimodal volcanic rocks atop the crystalline basement point to the rifting of the proto-North American continent Laurentia.
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Mount McKay, a mafic sill related to volcanism of the Midcontinent Rift System in Thunder Bay, Ontario. During the Mesoproterozoic era of the Precambrian period 1,109 million years ago, northwestern Ontario began to split apart to form the Midcontinent Rift System, also called the Keweenawan Rift. Lava flows created by the rift in the Lake Superior area were formed from basaltic magma. The upwelling of this magma was the result of a hotspot which produced a triple junction in the vicinity of Lake Superior.
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It consisted of roughly 90 percent uniform rhyodacitic pumice, which contained about 10 percent phenocrysts, the rest made up of crystalline andesite scoria and mafic crystals. The eruption released aerosol that lowered temperatures globally in the Northern Hemisphere, with estimates of for one to three years after the eruption. The temperature changes were possibly greater than the effects of the 1815 eruption of Mount Tambora. Mazama's climactic eruption produced stratospheric mass loadings of of sulfuric acid, with an estimated minimum sulfate degassing of during its eruption.
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At the south of Sisters Reach, there is a postglacial, basalt lava flow that lies on the eastern flank of Sitkum Butte (a cone that is older than this lava flow). The recent eruptive activity at Belknap Crater means that it is one of the youngest mafic volcanoes in the Oregon Cascades. There are about 6,500 people living within of Belknap Crater, with a population of about 362,000 within . However, most eruption hazards from basaltic volcanoes are generally restricted to within of the vent, with some exceptions.
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Manganiferous ilmenite is found in granitic rocks and also in carbonatite intrusions where it may also contain anomalous niobium. Many mafic igneous rocks contain grains of intergrown magnetite and ilmenite, formed by the oxidation of ulvospinel. Ilmenite also occurs as discrete grains, typically with some hematite in solid solution, and complete solid solution exists between the two minerals at temperatures above about 950 °C. Titanium was identified for the first time by William Gregor in 1791 in ilmenite from the Manaccan valley in Cornwall, southwest England.
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The Yellowknife greenstone belt, also called the Yellowknife Volcanic Belt, is an Archean greenstone belt in the southern Slave craton, Northwest Territories, Canada. It is mostly made of mafic volcanic rocks (basalt and andesite) and is bordered to the east by batholithic intrusions of the Western Granodiorite Complex and beyond to the north by the Duckfish Lake Granite. Intrusive equivalents (gabbro and diorite) are collectively known as the Kam Group. Most of the Yellowknife townsite and the Con and Giant gold mines are within the Kam Group.
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Active lava flows in volcanic region Tvashtar Paterae (blank region represents saturated areas in the original data). Images taken by Galileo in November 1999 and February 2000. The tidal heating produced by Io's forced orbital eccentricity has made it the most volcanically active world in the Solar System, with hundreds of volcanic centres and extensive lava flows. During a major eruption, lava flows tens or even hundreds of kilometres long can be produced, consisting mostly of basalt silicate lavas with either mafic or ultramafic (magnesium-rich) compositions.
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According to Hildreth (2007), Belknap Crater is a broad, low-angled shield volcano compared to other mafic (rich in magnesium and iron) volcanic cones. Belknap's summit cone rises about above the base shield volcano, and the volcano itself rises about above its surroundings. Oregon Route 242, which follows the course of the McKenzie River, passes through the lava fields produced by Belknap Crater, the Yapoah cinder cone volcano, and a number of other volcanic vents. These fields consist of black, basaltic lava and encompass an area of .
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The Mohs hardness is 4.5, and the specific gravity is 2.2. The species was established by Armand Lévy in 1825 and named after William Phillips. French authors use the name Christianite (after Christian VIII of Denmark), given by A. Des Cloizeaux in 1847. Phillipsite is a mineral of secondary origin, and occurs with other zeolites in the amygdaloidal cavities of mafic volcanic rocks: for example in the basalt of the Giants Causeway in County Antrim, and near Melbourne in Victoria; and in Lencitite near Rome.
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As gradually an unstable pulsating column formed, fed only by the most evolved magma due to upward migration of the fragmentation surface, reduced magma eruption rate, and/or activation of fractures, the Plinian phase ended. Emissions consisted of pumice and dark colored volcanic rock (scoria). The mafic minerals cover smaller areas than the more acidic members, also indicating a decrease of explosivity over the course of the eruption. The eruption column caused a large pumice-fall deposit to the east of the source area.
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The groundmass contains plagioclase, pyroxene, silicon dioxide and oxides of iron and titanium. The composition of Ciomadul's rocks has been fairly constant throughout its evolution albeit with two shifts 1 million and 650,000 years before present, and this diversity of its components indicate that the genesis of Ciomadul magmas involved mixing between felsic and mafic magma. A large proportion of crystals in the rocks consists of antecrysts and xenocrysts, making radiometric dating of the rocks difficult. These include the amphibole, biotite, feldspar and zircon.
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As the Archean Earth was hotter than the present, formation of felsic volcanic rocks may differ from the modern plate tectonics. Archean felsic volcanic rocks are distributed only in the preserved Archean greenstone belts, where deformed sequences of volcanic-sedimentary rocks are common. Felsic volcanic rocks are rare in the early Earth and only contribute to less 20% of rocks in the Archean greenstone belts worldwide. Nonetheless, mafic volcanic rocks (such as basalt and komatiite, silicate content <52%) occupy about 50% in the greenstone belts.
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The oldest rocks that are part of the Vishnu Basement Rocks is the Elves Chasm pluton. It consists of metamorphosed mafic (hornblende-biotite tonalite) and intermediate-composition plutonic rocks (quartz diorite). Within it, there are tabular amphibolite bodies that might be dikes, that have been dated at about 1.84 billion years ago. It is regarded to be an older granodioritic pluton that was exposed by erosion prior to being buried by the original volcanic and submarine sedimentary rocks of the Granite Gorge Metamorphic Suite.
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Seamounts are volcanic mountains which rise from the seafloor. The unlimited supply of water surrounding these volcanoes can cause them to behave differently from volcanoes on land. The lava emitted in eruptions at Bowie Seamount is made of basalt, a common gray to black or dark brown volcanic rock low in silica content (the lava is mafic). When basaltic lava makes contact with the cold sea water, it may cool very rapidly to form pillow lava, through which the hot lava breaks to form another pillow.
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The Tidekelt region has up to 25 million tons of salt brines, with a yield of 70 percent sodium chloride. There are some indications of platinum in the Makalondi District, south of Liptako, associated with chromite lenses in gabbros, anorthosite and chloritoschists. Ophiolites in the Abuzegueur overthurst, in the Air region also show potential for platinum mineralization and may also have chromite, nickel and cobalt. The Fantio deposit in the Liptako area has heavily weathered ultra-mafic rocks, with 0.8 percent nickel, totaling up to as much as 200,000 tons.
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The oldest volcanic activity at Lascar occurred between 220,000 and less than 50,000 years ago. Activity has alternated between the eastern and western part of the volcano during its history. The eastern edifice formed first (stage I), erupting andesite containing pyroxene, and eventually forming the Chaile and Saltar pyroclastic flows. The oldest mafic andesites are less than 43,000 years old, while the Chaile and Saltar pyroclastic flows erupted over 26,500 years ago. An alternative dating scheme considers Chaile to be 47,000 ± 16,000 years old and Saltar 167,000 ± 9,000 years old.
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At the time preceding the eruption, the magma chamber had a thermal stratification; injections of mafic magmas had heated the magma chamber and induced convection. A volatile phase containing chlorine formed inside the magma chamber and quickly removed most sulfur from the magma. This sulfur extraction was facilitated by the high oxygen content of the magma, which allowed the formation of sulfur dioxide. Water is a principal volatile involved in the processes of Plinian eruptions; the water content of the Soncor and Piedras Grandes magmas was about 4–5%.
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The 15 major plates Plate tectonics map from NASA This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust and uppermost mantle, together referred to as the lithosphere. The plates are around thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium) and continental crust (sial from silicon and aluminium). The composition of the two types of crust differs markedly, with mafic basaltic rocks dominating oceanic crust, while continental crust consists principally of lower-density felsic granitic rocks.
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Three suites of intrusive and volcanic rocks are found in the Kutai Basin, and have been used to constrain the Tertiary stratigraphy . The felsic Nyaan volcanics, dated to 48-50 Ma may be related to the extensional tectonics that initiated basin formation. In some locations, the Nyaan volcanics and equivalents are at the base of the Tertiary sedimentary succession, while at other locations bedded tuffs, agglomerates and reworked pyroclastics are part of the late Eocene succession. The Sintang Intrusive suite are mafic to felsic and have a fine crystalline nature which indicates high level emplacement.
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Final breakup formed a large group of mafic dike and sill swarms in the North American provinces 2.2–2.1 billion years ago. By the Paleoproterozoic era Kenorland had already rifted apart, and the TGB formed a small part of the supercontinent Columbia starting 1.9–1.8 billion years ago. Eastern India, Australia, Laurentia, Baltica, North China, the Amazon shield and portions of Antarctica formed the landmass until it ruptured 1.5–1.4 billion years ago. In the late Mesoproterozoic era 1.1 billion years ago, the Temagami belt was part of another supercontinent.
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Many rounded to subangular felsic and mafic volcanic fragments are known to occur in the unit, as well as rare quartz vein fragments and one fragment of white chert. The conglomerate unit passes laterally and vertically into thin bedded deposits. These thin bedded deposits are interpreted to be turbidites that originated from a felsic volcanic vent at the western end of Link Lake. Many dark green, highly vesicular, iron-rich tholeiitic basalts occur in the Turtle Lake Formation, and are interbedded with thin-bedded wackes on the southern limb of the Tetapaga Syncline.
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Some of siliceous rock types are suspected of being primary chemical precipitates from Paleoproterozoic ocean water. The south end of the Mint Wash Pluton, has intruded into Paleoproterozoic mafic, metavolcanic rocks that include basalt lava flows and Paleoproterozoic intrusive rocks, hornblende-rich gabbro-norite, gabbro, and gabbro-diorite. These sedimentary, metasedimentary, and metavolcanic rocks were deposited, deformed, and intruded contemporaneously with the Paleoproterozoic schists of the Vishnu Basement Rocks found in the Grand Canyon. The rocks intruded by the Mint Wash Granodiorite are also part of the same tectonostratigraphic terrane, Yavapai tectonic province.
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Pyroxenes have a general structure formula of XY(Si2O6), where X is an octahedral site, while Y can vary in coordination number from six to eight. Most varieties of pyroxene consist of permutations of Ca2+, Fe2+ and Mg2+ to balance the negative charge on the backbone. Pyroxenes are common in the Earth's crust (about 10%) and are a key constituent of mafic igneous rocks. pp. 612–13 Amphiboles have great variability in chemistry, described variously as a "mineralogical garbage can" or a "mineralogical shark swimming a sea of elements".
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The Hogland Series are a series of Subjotnian sedimentary rocks exposed in the island of Gogland (), the Sommer Islands and the nearby sea bottom in the Gulf of Finland. The series encompass quartz-rich conglomerates and breccias plus some volcanic rocks of mafic composition in the form of lava flows and some more silica-rich igneous rocks including quartz-porphyry. The porphyries, which lie at the top the pile, share their origin with the rapakivi granites found nearby. An exhumed Subjotnian erosion surface is exposed on the island.
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The letter-based Chappell & White classification system was proposed initially to divide granites into I-type (igneous source) granite and S-type (sedimentary sources). Both types are produced by partial melting of crustal rocks, either metaigneous rocks or metasedimentary rocks. M-type granite was later proposed to cover those granites that were clearly sourced from crystallized mafic magmas, generally sourced from the mantle. However, this proposal has been rejected by studies of experimental petrology, which demonstrate that partial melting of mantle peridotite cannot produce granitic melts in any case.
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Rare feldspathoid-rich mafic rocks, akin to alkali basalts, may have Na2O + K2O contents of 12% or more. The abundances of the lanthanide or rare-earth elements (REE) can be a useful diagnostic tool to help explain the history of mineral crystallisation as the melt cooled. In particular, the relative abundance of europium compared to the other REE is often markedly higher or lower, and called the europium anomaly. It arises because Eu2+ can substitute for Ca2+ in plagioclase feldspar, unlike any of the other lanthanides, which tend to only form 3+ cations.
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Syenite QAPF diagram that shows the quartz (Q), alkali feldspar (A), and plagioclase (P) composition of syenite leucocratic variety of nepheline syenite from Sweden (särnaite) Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). Some syenites contain larger proportions of mafic components and smaller amounts of felsic material than most granites; those are classed as being of intermediate composition. The volcanic equivalent of syenite is trachyte.
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The tenement straddles the contact between granites and greenstone belt of the Mara-Musoma goldfield. Approximately two-thirds of the tenement is underlain by granitic rock types while the north western third comprises sub- cropping volcanics of mainly mafic to intermediate composition of the Nyanzian System. Twof granite occur in the southern third of the property but most of the granite is covered by extensive mbugu plains. The volcanic rocks outcrop as a NE-SW trending range of hills and about half of the 4 km of strike length is exposed within the property boundary.
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However, it is now known that Cushetunk Mountain, as well as other intrusive bodies in the Newark Basin, are at least 10 million years older than the Watchungs, which implies that erosion and/or uplift must have occurred after Cushetunk Mountain was intruded in order to allow the Watchungs to form at the surface.Armstrong, R. L., Besancon, J. A Triassic time scale di-lemma: K-Ar Dating of Upper Triassic Mafic Igneous Rocks, Eastern U.S.A. and Canada, and Post-Upper Triassic Plutons, Western Idaho, U.S.A. Eclogae Geol. Helv., Vol. 63, p.
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This included new geochemical and geochronometric data for the Baldface Mountain and Satah Mountain volcanic fields, as well as for Nazko Cone. The data obtained indicated that volcanism in the two volcanic fields were contemporaneous with the Itcha Range shield volcano and that both fields agree with the vector of the North American Plate motion over a hotspot in the British Columbia Interior. It was also noted that the trace and rare-earth element patterns of mafic lavas in the Anahim Volcanic Belt are similar to ocean island basalts, providing more evidence for a hotspot.
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Stage 3 began with a crust made of mafic (high in iron and magnesium) and ultramafic rocks such as basalt. These rocks were repeatedly recycled by fractional melting, fractional crystallization and separation of magmas that refuse to mix. An example of such a process is Bowen's reaction series. One of the few sources of direct information on mineralogy in this stage is mineral inclusions in zircon crystals, which date back as far as 4.4 Ga. Among the minerals in the inclusions are quartz, muscovite, biotite, potassium feldspar, albite, chlorite and hornblende.
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The composition of a magma is the primary control on which mineral is crystallized as the melt cools down past the liquidus. For instance in mafic and ultramafic melts, the MgO and SiO2 contents determine whether forsterite olivine is precipitated or whether enstatite pyroxene is precipitated. Two magmas of similar composition and temperature at different pressure may crystallize different minerals. An example is high-pressure and high-temperature fractional crystallization of granites to produce single-feldspar granite, and low-pressure low-temperature conditions which produce two-feldspar granites.
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The higher viscosity means that, when melted, a granitic magma will tend to move in a larger concerted mass and be emplaced as a larger mass because it is less fluid and able to move. This is why granites tend to occur as large plutons, and mafic rocks as dikes and sills. Granites are cooler and are therefore less able to melt and assimilate country rocks. Wholesale contamination is therefore minor and unusual, although mixing of granitic and basaltic melts is not unknown where basalt is injected into granitic magma chambers.
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Both examples show large rounded spots in the hand specimens; they are pseudoleucites, and under the microscope prove to consist of orthoclase, nepheline, sodalite and decomposition products. These have a radiate arrangement externally, but are of irregular structure at their centres; in both rocks melanite is an important accessory. The missourites are more mafic and consist of leucite, olivine, augite and biotite; the leucite is partly fresh partly altered to analcite, and the rock has a spotted character recalling that of the leucite-syenites. It has been found only in the Highwood Mountains of Montana.
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Up to the middle 20th Century the upper crust in continental regions was seen to consist of felsic rocks such as granite (sial, for silica- aluminium), and the lower one to consist of more magnesium-rich mafic rocks like basalt (sima, for silica-magnesium). Therefore, the seismologists of that time considered that the Conrad discontinuity should correspond to a sharply defined contact between the chemically distinct two layers, sial and sima. However, from the 1960s onward this theory was strongly contested among geologists. The exact geological significance of the Conrad discontinuity is still not clarified.
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These weathering profiles are capped by an igneous deposit of an estimated 3.7-3.6 Ga which may be a pyroclastic deposit or a mafic sandstone, similar to paleosols buried beneath igneous deposits on Earth. These stratigraphic profiles appear to be up to 200 m in thickness, with individual layers of 10 m in thickness or less. This stratigraphy reflects the possible cooling and drying of Noachean Mars, and may preserve organic matter or other biosignatures because of the exceptionally high clay content (~50 wt %) and clay mineralogy (2:1 smectites) of these buried rocks.
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Much of the terrain of central Massachusetts is formed by domes that were created in the Cambrian and Ordovician. In fact, the Ammonousuc and Partrdige formation mafic and felsic volcanic rocks ring uplifted domes, dating to the Ordovician. The Clough quartzite is younger, from the Silurian. The Acadian orogeny, from 425 to 270 million years ago was the most extensive and long lasting Appalachian orogeny, as the microcontinent Avalonia (also referred to as the Avalon terrane) collided followed by a full collision between Europe, Gondwana (western Africa) and North America to form the supercontinent Pangea.
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This collision caused subduction and volcanism in the Proto-Antillean area and likely resulted in continental uplift of the Bahama Platform and changes in sea level. The Greater Antilles have continuously been exposed since the start of the Paleocene or at least since the Middle Eocene (66-40 million years ago), but which areas were above sea level throughout the history of the islands remains unresolved. The oldest rocks in the Greater Antilles are located in Cuba. They consist of metamorphosed graywacke, argillite, tuff, mafic igneous extrusive flows, and carbonate rock.
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The Barberton Mountain is a well preserved pre-3.0 Ga granite-greenstone terrane. The greenstone belt consists of a sequence of mafic to ultramafic lavas and metasedimentary rocks emplaced and deposited between 3.5 and 3.2 Ga. The granitoid rocks were emplaced over a 500 million year time span and can be divided into two suites. The TTG suite (emplaced approximately 3.5–3.2 Ga) contains tonalites, trondhjemites and granodiorites; and the GMS suite (emplaced approximately 3.2–3.1 Ga) includes granites, monzogranites and a small syenite–granite complex. According to a study by Yearron et al.
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These boulder fields in southeastern Pennsylvania and central New Jersey formed from a group of diabase sills in Newark Basin. The sills were formed when stretching of the Earth's crust allowed mafic magma to travel up from the upper mantle inject into the sedimentary basin 200 million years ago (early Jurassic Period). Phenocrysts of two minerals that had crystallized in the upper mantle, olivine and pyroxene, quickly settled out of the magma and collected along the base of the sills. When fully solidified, this crystal-rich layer formed a separate rock unit thick.
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This smelting and refining process contributes to about one-third of the total nickel output in Canada. In the Cape Smith Belt of northern Quebec, the Raglan Mine lies in copper-nickel deposits of the ultramafic Katiniq Suite sills. The Katiniq Suite sills are also within an area that is presently explored for nickel, copper and platinum group element deposits. Copper, nickel and platinum group elements are associated with mafic-ultramafic rocks in the Labrador Trough that were formed during a period of magmatism 1,883 to 1,870 million years ago.
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Continental and oceanic terranes began to be added to western South America in the Mesozoic. In north-central Ecuador, the Peltetec- Portovelo fault marks the suture between the pre-existing South American craton and the Amotape-Chaucha terrane, which partially subducted beneath a preexisting Mesozoic continental arc system. The Triassic mafic and granitoid rocks of the El Oro metamorphic complex and the component eclogite, blueschist and amphibolite are known as the Raspas metamorphic complex. This section of the terrane was previously subducted but brought to the surface with tectonic activity.
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The Ogeechee River basin contains parts of the Piedmont and Coastal Plain physiographic provinces, which extend throughout the southeastern United States. This boundary follows the contact between older crystalline metamorphic rocks of the Piedmont Province and the younger unconsolidated Cretaceous and Tertiary sediments of the Coastal Plain Province. Other rock types found in the basin include metasedimentary rock, schists and phyllites, felsic and mafic metavolcanic rocks, and amphibolite. Coastal Plain sediments overlap the igneous and metamorphic rocks of the southern edge of the Piedmont Province at the Fall Line.
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The oldest rocks in Peru date to the Precambrian and are more than two billion years old. Along the southern coast, granulite and charnockite shows reworking by an ancient orogeny mountain-building event. Situated close to the Peru- Chile Trench, these rocks have anomalously high strontium isotope ratios, which suggest recent calc-alkaline volcanism. In the Eastern Cordillera of Peru, Precambrian magmatism in the Huanaco region produced ultramafic, mafic and felsic rocks, including serpentinite, meta-diorite, meta-gabbro, meta- tonalite and diorite and granite that intruded after the first phase of orogenic tectonic activity.
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Erosional remnants of sills form the prominent mesas of North Mesa, Peaked Hill and Round Hill, the latter two of which consist of tholeiitic basalt and alkali basalt respectively. A major episode of Tertiary magmatism related to the opening of Baffin Bay emplaced mafic intrusions and volcanic rocks on Baffin Island and in West Greenland. Basaltic breccias and lavas on Baffin Island are exposed mainly along a narrow coastal strip between Cape Dyer and Cape Searle. They have a total thickness of over and are bounded in the north by minor intrusions.
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This area contains many small shield volcanoes and cinder cones of mainly alkalic intraplate basalt with fractionated intermediate alkalic products, subordinate subalkaline mafic lavas, and several rhyolites as secondary products. There are about 205 vents that were active between 4.2 million and 600 thousand years ago. Seismic activity around Adams is very low and it is one of the quietest volcanoes in Oregon and Washington. It is monitored by the Pacific Northwest Seismic Network and the Cascades Volcano Observatory via a seismic station on the southwest flank of the mountain.
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These volcanoes are unlike others throughout the Garibaldi Volcanic Belt in that they are mainly composed of volcanic rocks with mafic compositions, including alkaline basalt and hawaiite. The different magma compositions might be related to a smaller degree of partial melting in the Earth's mantle or a descending plate edge effect. The oldest volcano in the group, known as Sham Hill, is a high volcanic plug with a potassium-argon date of one million years. It is about wide and its uncovered glaciated surface is strewn with glacial erratics.
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The oldest rocks in Peru date to the Precambrian and are more than two billion years old. Along the southern coast, granulite and charnockite shows reworking by an ancient orogeny mountain building event. Situated close to the Peru-Chile Trench, these rocks have anomalously high strontium isotope ratios, which suggest recent calc-alkaline volcanism. In the Eastern Cordillera of Peru, Precambrian magmatism in the Huanaco region produced ultramafic, mafic and felsic rocks, including serpentinite, meta-diorite, meta-gabbro, meta-tonalite and diorite and granite that intruded after the first phase of orogenic tectonic activity.
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The Alexander terrane is made up of Cambrian-Ordovician quartz sandstone, limestone and mafic volcanic rocks, Ordovician-Silurian carbonates, siltstone and calcareous mudstone, as well as Devonian-Triassic siltstone, sandstone and carbonate. Geologists have subdivided the Alexander terrane into the Saint Elias subterrane in the Yukon and British Columbia (the Craig subterrane is located in Alaska). Some have suggested that the two subterranes were rifted off of Baltica and then brought together during the Silurian-Devonian Klakas orogeny. The Wrangellia terrane linked with the Alexander is somewhat younger.
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Carbonates are highly soluble, especially in acidic environments; the elements hosted by them - calcium, magnesium, manganese and strontium - are strongly leached. Serpentinite - oxidized and hydrolized low-silicon, iron- and magnesium-rich oxide igneous rocks - are progressively weathered through this zone. Ferromagnesian minerals are the principal hosts for nickel, cobalt, copper and zinc in sulfide-poor mafic and ultramafic rocks, and are retained higher in the profile than sulfide-hosted metals. They are leached from the upper horizons and reprecipitate with secondary iron-manganese oxides in the mid- to lower saprolite.
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The Great Dyke of Zimbabwe-I: tectonic setting, stratigraphy, petrology, structure, emplacement and crystallisation. In: Prendergast, M.D., Jones, M.J. (Eds.), Magmatic sulphides-the Zimbabwe volume. Institution Mining Metallurgy, London, 1–20. Stratigraphically each sub-chamber is divided into a lower Ultramafic Sequence of dunites, harzburgites, olivine bronzitites and pyroxenites together with narrow layers of chromitite that constitute the bases of cyclic units and that are extensively mined along the Great Dyke, and an upper Mafic Sequence mainly consisting of a variety of plagioclase-rich rocks, such as norites, gabbronorites and olivine gabbros.
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The thickness of the crust beneath the rift is disputed, as the structures of the rift deep beneath the surface are unknown. The difference in thickness of the crust, between the crust under the rift and that under the surrounding areas, has been bounded to be less than . Although some seismic data is evidence for a rise in the Lithosphere-Asthenosphere boundary, other researchers have claimed that there are deep structures which influence seismic activity, and that the lower crusts is intruded by mafic sills. They interpret the extension as a pure shear process.
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Rare Earth proponents argue that plate tectonics and a strong magnetic field are essential for biodiversity, global temperature regulation, and the carbon cycle. The lack of mountain chains elsewhere in the Solar System is direct evidence that Earth is the only body with plate tectonics, and thus the only nearby body capable of supporting life. Plate tectonics depend on the right chemical composition and a long- lasting source of heat from radioactive decay. Continents must be made of less dense felsic rocks that "float" on underlying denser mafic rock.
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Rhyolitic magmas generally produce finer grained material compared to basaltic magmas, due to the higher viscosity and therefore explosivity. The proportions of fine ash are higher for silicic explosive eruptions, probably because vesicle size in the pre-eruptive magma is smaller than those in mafic magmas. There is good evidence that pyroclastic flows produce high proportions of fine ash by communition and it is likely that this process also occurs inside volcanic conduits and would be most efficient when the magma fragmentation surface is well below the summit crater.
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The oldest Precambrian rocks in Wisconsin are late Archean quartzofeldspathic gneiss, migmatite and amphibolite up to three billion years old and igneous rock such as the granite of the Puritan Quartz Monzonite. Mafic and intermediate metavolcanic rocks together with metasedimentary rocks are found in the Ramsey Formation in Iron County and iron formations in Jackson County. The metasediments and metavolcanics formed first, followed by granites more than 2.7 billion years ago. The rock record contains an uncertain age gap with younger 2.3 billion year old Proterozoic quartzofeldspathic and migmatite gneiss, with amphibolite and biotite schist.
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Near Merrill are metamorphosed ultramafic and mafic intrusive rocks with a distinctive magnetic signature. From 1.7 to 1.6 billion years ago granite and rhyolite emplaced in south-central Wisconsin. The Baraboo and Waterloo Quartzite in the south and the Barron Quartzite in the northwest are slightly younger, along with the slate, dolomite, conglomerate and chert included in Wolf River rocks at Rib Mountain, Mosinee Hill and the McCaslin Quartzites. The Wolf River Batholith spans from Glade County in the north to the northern part of Portage County in the south.
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When the giant Mackenzie dike swarm intruded into the Canadian Shield, it partly uplifted and intruded the Slave craton in the Northwest Territories and Nunavut. This was the last major event to affect the core of the Slave craton, although later on some younger mafic magmatism registered along its boundaries. This includes the magmatic events that formed the 723 million year old Franklin Large Igneous Province and the 780 million year old Hottah gabbro sheets. Since the Mackenzie dike swarm intruded the Slave craton, the craton has been repeatedly submerged under seas.
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The radius of the crater floor, which is the current inner vent, is around , while the radius of its rim is . The crater floor lies at , and the rim lies above that, giving the walls an average slope of 34–35 degrees (close to the angle of repose). The western wall is cut by two long, dacitic lava flows: probably the remnants of a dome or an eruption. The crater is surrounded by debris from its 1932 eruption, and topped by layers— thick—of mafic scoria and ash.
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The Stac Fada Member is a distinctive layer towards the top of the Mesoproterozoic Bay of Stoer Formation, part of the Stoer Group (lowermost Torridonian Supergroup) in northwest Scotland. This rock unit is generally thick and is made of sandstone that contains accretionary lapilli and many dark green glassy fragments of mafic composition. Evidence for a meteorite impact in the area of the Minch or near Lairg has been published and refined in a series of studies from 2008 to 2019. The unit dates to approximately 1.2 billion years ago.
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Outcrops of the resulting Shoo Fly Complex (made of schists and gneisses) and younger Calaveras Complex (a mélange of shale, siltstone, and chert with mafic inclusions) are now found in the western side of the park. Later volcanism in the Jurassic intruded and covered these rocks in what may have been magmatic activity associated with the early stages of the creation of the Sierra Nevada Batholith. 95% of these rocks were eventually removed by uplifted-accelerated erosion. Most of the remaining rocks are exposed as 'roof pendants' in the eastern metamorphic zone.
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In the Troodos ophiolite it was observed from the variation in magma types, which can be seen to go from evolved to less evolved mafic rocks in localised cross cutting field relationships implying the presence of more than one magma chamber that cuts other exhausted ones. This has now been shown to be supported from other ophiolite bodies such as Oman. In terms of ophiolite emplacement, there was a problem of how to uplift dense oceanic lithosphere through 5–6 km of water and onto continents. This process, however it happened, was coined obduction.
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The Sand Mountain Volcanic Field was formed after magma entered rock that was fractured by faulting related to subsidence of the High Cascades graben. Beginning as dikes, these bodies of magma moved through conduits to separate volcanic vents at the surface. The initial magma was basaltic, though this was replaced several hundred years later by more evolved, basaltic andesite magma. Eruptions at Sand Mountain Field were fed by two or three magma chambers, including a number of mafic magma sources over a brief span of distance and time.
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These flows vary in age from are 3,850 ± 215 years BP to 2,750 years BP. The field also includes an extensive tephra deposit, which encompasses an area of and has a volume of . This tephra field is notable because it has a much greater volume and extent than tephra produced by other mafic volcanoes in the central Oregon Cascades. Additionally, the tephra exhibits uniformity with a fine mode grain size of to and a lack of lapilli. These tephra deposits vary in age from 3,440 ± 250 to 1,600 years BP, according to radiocarbon dating.
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The Rhenohercynian basin disappeared when the continent Gondwana collided with Laurussia in the course of the Carboniferous period (the Hercynian orogeny). The sedimentary rocks in the basin were thrust in a series of piggyback basins over the northern foreland (the London-Brabant Massif). These rocks now form the folded sequences of Cornwall, the Ardennes, the Eifel and the Harz. From the Frasnian age (380 million years ago) the mafic volcanism ended, and the basin came locally under compressional stress, which led to folding and thrusting in the sedimentary rocks.
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Vents range from deeply eroded complexes to recently active volcanoes, with most of the region mantled by normally polarized rock produced within the past 730,000 years. The mountain also forms part of a group of more than 30 large shield volcanoes and stratovolcanoes that form a segment of Pleistocene-to-Holocene-epoch volcanic vents that produced mafic lava (rich in magnesium and iron). Three Fingered Jack includes several, overlapping cinder cones and composite cones over underlying lava flows from shield volcano activity. These volcanic edifices and their lava flow deposits cover an area of .
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The high elevation of Matuyama-aged rocks east of Santiam Pass, coupled with exposure of Brunhes- aged rocks to the west, imply the presence of a northward-trending normal fault. Part of a mostly mafic chain of volcanoes between the Three Sisters and Mount Jefferson, Hogg Rock has magma with an intermediate composition. A tuya, Hogg Rock is also considered a small lava dome with the flat top typically observed for tuya volcanoes. Unlike most lava domes in the Cascades, which are made of dacite or rhyodacite, Hogg Rock is comprised by andesitic lava.
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If the melt contains enough dissolved gas, the rate of exsolution will determine the magmas rate of ascension. Mafic melts contain low levels of dissolved gases whereas felsic melts contain high levels of dissolved gases. The rate of eruption for volcanoes of different compositions is not the controlling factor of gas emission into the atmosphere. The amount of gas delivered by an eruption is controlled by the origin of the magma, the crustal path the magma travels through, and several factors dealing with P-T-x at the Earth's surface.
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In some stocks magma mixing appears to have occurred during formation; in Alto de la Alumbrera first felsic and at the end mafic rocks were formed. Several dykes and stocks were injected into andesite during the formation of Bajo de la Alumbrera. Many of these stocks have suffered hydrothermal alteration extending into surrounding rocks shortly after their formation including propylitic alteration, but the later stocks show no evidence of alteration. This pattern probably occurred because strong volcanic activity during the earliest intrusions did leak away fluids before they could trigger alteration.
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Taapaca is mostly formed by potassium-rich dacite, although andesite was erupted early during its activity, and one occurrence of rhyolite is reported. The composition of the rocks has been relatively uniform over the history of the volcano, and is characterized by a calc-alkaline suite of magmas. Visible minerals found in rocks erupted at Taapaca include amphibole, apatite, biotite, clinopyroxene, orthopyroxene, magnetite and hematite, plagioclase, quartz, sanidine and titanite. Dacitic rocks contain mafic inclusions, and such inclusions become increasingly common the younger the rocks they are embedded in are.
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The presence of mafic inclusions indicates that magma mixing occurs at Taapaca, with renewed eruptive episodes having been triggered by the injection of new andesitic magma into preexisting dacitic magma chambers. These dacitic magma chambers appear to have relatively small volumes, with little movement of the magma within the chamber except for the episodes where the chambers were heated by new magma injection. Based on geothermometry, a temperature of has been inferred for the dacites. The formation of the magma has been hypothesized to occur in several steps.
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Magmatic foliations and mafic enclaves usually indicate radially increasing strains normal to the pluton contact and extensional strains parallel to it. Magmatic fabrics will not record information of the stoping process as they are only formed near the end of the pluton emplacement. Furthermore, any magmatic fabrics that are recorded are likely to be affected by strain. Therefore, the causes of the magmatic fabrics may not be discernable, and at best can only give inferences to the mechanisms for emplacement of the pluton, or magma chamber internal mechanisms.
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To date, the discontinuous operation of Kanichee Mine has produced 4.2 million pounds of metal. The Kanichee area is associated with an igneous intrusion that has been termed the Kanichee layered intrusive complex. This roughly oval-shaped intrusive complex is part of a volcanic belt characterized by felsic and mafic metavolcanic rocks called the Temagami Greenstone Belt. Kanichee is one of the three most notable mines in the volcanic belt, others include the Sherman Mine in Chambers and Strathy townships and the Copperfields Mine on Temagami Island in Lake Temagami.
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The first successful identification of a strong infrared spectral signature from surficial carbonate minerals of local scale (< 10 km²) was made by the MRO-CRISM team. Spectral modeling in 2007 identified a key deposit in Nili Fossae dominated by a single mineral phase that was spatially associated with olivine outcrops. The dominant mineral appeared to be magnesite, while morphology inferred with HiRISE and thermal properties suggested that the deposit was lithic. Stratigraphically, this layer appeared between phyllosilicates below and mafic cap rocks above, temporally between the Noachian and Hesperian eras.
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She is best known for her work that links the kinetics of bubble and crystal formation to the behaviour of volcanic materials, but has worked on problems that span from the chemical to physical to social aspects of volcanism. She has worked with all the US volcano observatories and served on the scientific advisory committee for the island of Montserrat. Her research uses a combination of volcanology, igneous petrology, kinetics, microscopy and fluid dynamics with a focus on mafic volcanoes. This includes channel development in Hawaiian lava flows and volcanic ash formation in eruptions.
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The Noranda Caldera is a well-known large subaqueous Archean caldera complex within the Blake River Megacaldera Complex, Quebec, Canada. The caldera contains a 7-to-9-km-thick succession of bimodal mafic-felsic tholeiitic to calc-alkaline volcanic rocks which were erupted during five major series of volcanic activity.ASH FALL: Newsletter of the Volcanology and Igneous Petrology Division Geological Association of Canada Retrieved on 2007-09-22 The metallogenic impact of the Noranda Caldera is well-known, but the importance of the New Senator Caldera and Misema Caldera remains to be evaluated.
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123–132 & 194–197, Freeman, While most layered intrusions are Archean to Proterozoic in age (for example, the Paleoproterozoic Bushveld complex), they may be any age such as the Cenozoic Skaergaard intrusion of east Greenland or the Rum layered intrusion in Scotland. Although most are ultramafic to mafic in composition, the Ilimaussaq intrusive complex of Greenland is an alkalic intrusion. Layered intrusions are typically found in ancient cratons and are rare but worldwide in distribution. The intrusive complexes exhibit evidence of fractional crystallization and crystal segregation by settling or floating of minerals from a melt.
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Late Neoarchean rocks spread over the whole Eastern Block. High to medium-grade gneiss and ultramafic extrusive rocks, especially komatiites occur in eastern Hebei, eastern Shandong, northern Liaoning and southern Jilin areas, whereas low to medium-grade granite-greenstone terranes are seen in western Shandong, southern Liaoning and Anshan areas. All rocks were formed in a geologically brief period, between 2.55 and 2.5 billion years ago. In this period, mafic and felsic lava erupted and granitoids intruded the whole Eastern Block, followed by a 2.5 billion-year-old regional metamorphism.
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The metamorphic event has an anticlockwise pressure-temperature-time path with nearly isobaric cooling. The anti-clockwise path indicates the metamorphism is related to the intrusion of magma within the Earth's crust. During prograde and peak metamorphism, temperature and pressure are increased and a large amount of mafic material is added to the crust, whereas after the peak metamorphism, the intrusion of magma stops, resulting in isobaric cooling. Structurally, these Late Neoarchean rocks are dome-shaped, for example, the Jinzhou dome in southern Liaoning and the Huadian dome in southern Jilin.
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390x390px At around 2.7 billion years ago, a Large Igneous Province event with massive magmatism took place. It was caused by a mantle plume activity, which led to the stretching of the crust, the intrusion of magma and thus the melting of the lithosphere. Such a model can explain the eruption of ultramafic melts and thus the generation of komatiites and mafic rocks in Luxi granite-greenstone terrane. The axis of the plume consisted of hot ultramafic material with low viscosity, while the head of the plume brought cooler basaltic material.
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The igneous material is composed almost entirely of mafic and ultramafic rock such as gabbro and olivine-bearing pyroxenite. Mont Rougemont might be the deep extension of a vastly eroded ancient volcanic complex, which was probably active about 125 million years ago.A Hundred-Million Year History of the Corner Rise and New England Seamounts Retrieved on 2007-08-01 The mountain was created when the North American Plate moved westward over the New England hotspot, along with the other mountains of the Monteregian Hills. It forms part of the vast Great Meteor hotspot track.
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Because of these mixing mechanisms, lavas may have different compositions but similar appearances, or similar compositions with different appearances. The eruption that produced the Chaos Crags consisted of more than 90% mixed magma, and likely resulted from the interaction of felsic and mafic magmas. The Eagle Peak sequence, which includes the Chaos Crags, consists of seven dacite and rhyodacite lava domes and lava flows, along with pyroclastic rock deposits. The Chaos Crags consist of five small lava domes, made of rhyodacite, which line up with the western edge of the Mount Tehama caldera.
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Exposed rock formation on the southern slope of Mount Jackson, showing a mixed mafic/felsic breccia face The mountain is in height, with a prominence of and a saddle DEM of . Mount Jackson and the Welch Mountains demarcate the central Black Coast, which is dissected by many inlets and is bounded on the west by Dyer Plateau of central Palmer Land, with elevation ranging between ,Riffenburgh, pp. 66– and on the west side of the central Black Coast. The two mountains rise above the ice shelf with reliefs of about towards the east.
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In order to produce a magma composition suitable for forming essexite the partial melting of the source rocks must be restricted, generally to less than 10% partial melting. This favors producing a melt rich in large-ion lithophile elements (LILE) such as K, Ba, Rb, Cs, Sr. The source melts of essexites contain more aluminium and alkali ions than available silica tetrahedra, which is why essexites crystallise nepheline instead of plagioclase. Higher than normal potassium favors the production of orthoclase, which is usually absent from most mafic igneous rocks.
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When these deep mantle rocks (serpentinite) and crustal rock (mafic igneous rocks) are heated up (metamorphosed) together, pounamu can be formed at their contact. The Dun Mountain Ophiolite Belt has been metamorphosed in western Southland and pounamu from this belt is found along the eastern and northern edge of Fiordland. The Anita Bay Dunite near Milford Sound is a small but highly prized source of pounamu. In the Southern Alps, the Pounamu Ultramafic Belt in the Haast Schist occurs as isolated pods which are eroded and found on West Coast rivers and beaches.
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Mount Washington is a deeply eroded volcano in the Cascade Range of Oregon. It lies within Deschutes and Linn counties and is surrounded by the Mount Washington Wilderness area. Like the rest of the Oregon Cascades, Mount Washington was produced by the subduction of the oceanic Juan de Fuca tectonic plate under the continental North American tectonic plate, forming during the late Pleistocene. Made mostly of mafic (rich in magnesium and iron) volcanic rock like subalkaline basalt and basaltic andesite, it has a volcanic plug occupying its summit cone and numerous dikes.
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Pleistocene deposits show evidence of erosion by glaciers. Holocene deposits, dated between 3,000 and 1,500 years old, encompass about half of the wilderness area, and they also occur outside the wilderness area at its northwestern and southern borders. alt=An eroded volcanic edifice rises above a forested region Whether Mount Washington is a stratovolcano or shield volcano is debated within the literature. Wood and Kienle (1990) refer to it as a "mafic shield volcano," and the Global Volcanism Program of the Smithsonian Institution also considers it a shield volcano with a pyroclastic cone.
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There are four major types of basalt and basaltic andesite in the central Cascades: early high-alumina olivine tholeiitic (HAOT) basalt, normal High Cascade HAOT basalt, North Sister basaltic andesites, and Mount Washington type basaltic andesites. Hughes (1990) argues that their differences could be the result of different magma sources or magma evolution in open systems. Mount Washington basaltic andesites are also considered one of the three distinct mafic rock types in the High Cascade platform, with North Sister basaltic andesites and normal basalts. The three groups all exhibit different major and trace element abundances.
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Mount Washington formed during the late Pleistocene epoch; the volcano itself is not older than a few hundred thousand years. Harris (2005) estimates that it has not erupted for more than 250,000 years, similar to Mount Thielsen; this date is supported by James, Manga, and Rose (1999). Paleomagnetic evidence suggests that the volcano and associated lava flows exhibit normal magnetic polarity. Its volcanic edifice was produced through the eruption of basaltic andesite and mafic volcanic ash, the latter being preserved as palagonite tuff along the northeastern and southwestern flanks of the summit cone.
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This back-arc volcanism that Tunupa is part of has an uncertain origin; one proposed process is delamination, whereby the lowermost mafic section of the crust and lithosphere underneath separates itself from the above lying layers. This separation process then triggers volcanic activity through either decompression melting, dehydration melting, increases in temperature, or some combination of these processes. Back-arc volcanism in the region started about 25-30 million years ago. East of Tunupa lie the Huayrana lavas, which are much older (Potassium-argon dating has yielded an age of 11.1 ± 0.4 million years ago).
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Even later, several mafic centres grew southwest and west of the Antofalla complex. Fumarolic activity continues to this day, the existence of geysers was reported in 1962 and traces of an extinct geyser such as sinter structures have been found at Botijuelas. There are reports that the main volcano "smoked" occasionally such as in 1901 and 1911 and Antofalla is sometimes incorrectly considered the highest active volcano in the world, but the Global Volcanism Program considers the complex as Pleistocene in age, and no clear evidence of Holocene activity is found.
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The behavior of Etna changed after the eruption, presumably due to the large volume of material erupted in the 1669 event and changes in the plumbing system it caused. After 1669, Etna's eruptions were smaller, shorter, and more sporadic with fewer flank eruptions, and mafic phenocrysts became more common in the lavas. The 1669 eruption has been defined as the starting point of a century-long cycle of activity that continues to this day and Etna's volcanic products are subdivided into pre-1669 and post-1669 formations in Italy's geological map.
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Lake Sentani lies at the foot of the Mesozoic mafic and ultramafic rocks of the Cyclops ophiolite mountains in a fault-controlled depression at an elevation of above sea level. Sentani is an irregularly shaped body with approximate maximum length extending from east to west of and, from north to south, of breadth. With a surface area of , Lake Sentani is the largest lake of the Intan Jaya region. Lake Sentani receives its water primarily from direct precipitation with an average annual rainfall around the lake of about , and by mountain streams.
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Modern science treats lamprophyres as a catch-all term for ultrapotassic mafic igneous rocks which have primary mineralogy consisting of amphibole or biotite, and with feldspar in the groundmass. Lamprophyres are not amenable to classification according to modal proportions, such as the system QAPF due to peculiar mineralogy, nor compositional discrimination diagrams, such as TAS because of their peculiar geochemistry. They are classified under the IUGS Nomenclature for Igneous Rocks (Le Maitre et al., 1989) separately; this is primarily because they are rare, have peculiar mineralogy and do not fit classical classification schemes.
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Experiments have provided many examples of the complexities that control which mineral is crystallized first as the melt cools down past the liquidus. One example concerns crystallization of melts that form mafic and ultramafic rocks. MgO and SiO2 concentrations in melts are among the variables that determine whether forsterite olivine or enstatite pyroxene is precipitated, but the water content and pressure are also important. In some compositions, at high pressures without water crystallization of enstatite is favored, but in the presence of water at high pressures, olivine is favored.
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Located southeast of Faial Island, it is a popular geochemical sampling and modeling site due to close proximity to the Azores and definitive representation of serpentinization from hydrothermal circulation and synthesis. Vent geology, biology, and fluid content make Rainbow comparable to other hot hydrothermal vents of the Azores such as Lucky Strike and Menez Gwen. However; chlorinity, metal concentration, and pH distinguish it from neighboring vent fields. As a hot, ultramafic-hosted vent field, pH levels of fluids are extremely low with much H2 and CH4 generated from water interactions with mafic igneous rocks.
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The Metolius River's basin sustains a wide array of plant life, large and small mammals, and more than 80 bird species. Black Butte last erupted during the Pleistocene; geologists have estimated its age at 0.4, 0.5, and 1.43 ± 0.33 million years ago. The duration of the eruptions that built the volcano remains unclear, though the activity likely coincided with large-scale block faulting in the vicinity of the Metolius Springs. Black Butte has a prominent volcanic cone and is made up of mafic (rich in magnesium and iron) basaltic andesite lava.
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The fault's steep escarpment contains exposed, alternating layers of basaltic andesite, breccia, and agglomerate from shield volcanoes, which mark the oldest rocks in the area. They are of Pliocene age, overlying diatomite, pumice, and tuffaceous sandstone layers. Most of the volcanoes in the Oregon Cascades are either scoria cones, small shield volcanoes, or lava fields, though the segment contains a number of basaltic andesite stratovolcanoes such as Mount McLoughlin. Black Butte is one such stratovolcano (also known as a composite volcano), with a mafic (rich in magnesium and iron) composition.
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The Northern group is composed of two cones, formed 126,000-90,000 years ago; the Southern group is larger, with two cones in the lagoon itself, and formed over a much larger and undetermined span of time. Most volcanic complexes in the field have a well-preserved scoria cone and lava apron, dotted with eruptive vents and lava flows. 42 eruptive units can be seen on the ground today. The San Quintín field is the only known location of intraplate-type mafic alkalic volcanism on the Baja California peninsula.
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Its lavas are made of basalt, a common grey to black or dark brown extrusive volcanic rock low in silica content (the lava is mafic) that is usually fine-grained due to rapid cooling of lava on the Earth's surface. Pāhoehoe is found at the volcano, which has a smooth, billowy, undulating, or ropy surface. A pāhoehoe flow typically advances as a series of small lodes and toes that continually break out from a cooled crust.Basaltic Lava Retrieved on 2008-02-13 It also forms lava tubes where the minimal heat loss maintains low viscosity.
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The Vishnu Basement Rocks were deposited as mafic and felsic volcanic rocks and sediments but were later metamorphosed and intruded by igneous rock. The Vishnu Basement Rocks is the name recommended for all Early Proterozoic crystalline rocks (metamorphic and igneous) exposed in the Grand Canyon region. They form the crystalline basement rocks that underlie the Bass Limestone of the Unkar Group of the Grand Canyon Supergroup and the Tapeats Sandstone of the Tonto Group. These basement rocks have also been called either the Vishnu Complex or Vishnu Metamorphic Complex.
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Trace elements were used to discover that older mounts created by the Cobb Hotspot contained more minerals like olivine and augite; both mafic minerals. Younger mounts created by the hotspot contain more minerals like calcic plagioclase, augite and pigeonite; they contain little to no olivine. These characteristics found at the younger mounts are like those found in basalts recovered from the Juan de Fuca Ridge. It is inferred that much of the difference in basalt composition along the chain is due to the time-dependent distance between hotspot and ridge.
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These anamolies may indicate that the inflation is of mafic composition, as rhyolite only poorly dissolves . Gravity change measurements also show an interaction between magma source, faults and the hydrothermal system. This uplift has been a cause of concern in light of the history of explosive activity of the volcanic field, with 50eruptions in the last 20,000 years; the current uplift may be the prelude of a large rhyolitic eruption. In particular, the scarce fumarolic activity implies that a large amount of gas is trapped within the magma reservoir, increasing the hazard of an explosive eruption.
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Volcanic activity would have started with volcaniclastic accumulations, like volcanic ash, quickly followed by vast outpourings of highly fluid basaltic lava during successive eruptions through multiple volcanic vents or in linear fissures. As mafic low viscosity lava reached the surface it rapidly cooled and solidified, successive flows built up layer upon layer, each time filling and covering existing landscapes. Hyaloclastites and pillow lavas were formed when the lava flowed into lakes, rivers and seas. Magma that did not make it to the surface as flows froze in conduits as dikes and volcanic plugs and large amounts spread laterally to form sills.
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The Younger Volcanic Complex, a unit of the Temagami Greenstone Belt made of mostly mafic volcanic rocks, is the main volcanic complex at Barton. A series of intrusions penetrate the complex and three major zones of deformation have been identified, namely the Northeast Arm Deformation Zone, the Link Lake Deformation Zone and the Net Lake-Vermilion Lake Deformation Zone. The Arsenic Lake Formation, a series of mostly dark green, iron-rich, massive and pillowed tholeiitic basalt lava flows, is the principal geologic formation at Barton Mine. Feldspar-phyric basalt lava flows contain tabular feldspar phenocrysts that range up to in cross section.
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There are two principal facies of lower Paleozoic rocks in Nevada. In the eastern part of the state, a north-trending fossil- rich carbonate shelf of Ordovician to Devonian age, termed the carbonate or eastern assemblage, gives way westward to a contemporaneous expanse of siliceous sedimentary deposits and minor mafic volcanic rocks termed the siliceous or western assemblage. Crafford assigned these two facies respectively to the shelf domain and the basin domain. The dark color of the western assemblage, the scarcity of carbonate rocks, and a near absence of shelly fossils, are generally interpreted to indicate a relatively deep-water depositional environment.
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As the Atlantic and Arctic oceans opened during the Mesozoic and into the Cenozoic, the Arctic Region underwent several stages of rifting, sedimentation, and magmatism. Dolerites collected from Svalbard and elsewhere in the Arctic are mafic intra-plate tholeiites characteristic of HALIP, which indicated that the LIP formed during the opening of the Arctic Ocean around 148–70 Ma. Seismic and magnetic analyses of the seafloor produced ages of 118–83 Ma. The HALIP is widely thought to have originated from a mantle plume, and the igneous activity of the province often tracked along a similar path as the Icelandic hotspot.
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A map showing the simplified geology of Cornwall A simplified map showing the granite intrusions and mafic igneous rocks of Cornwall The geology of Cornwall, England, is dominated by its granite backbone, part of the Cornubian batholith, formed during the Variscan orogeny. Around this is an extensive metamorphic aureole (known locally as killas) formed in the mainly Devonian slates that make up most of the rest of the county. There is an area of sandstone and shale of Carboniferous age in the north east, and the Lizard peninsula is formed of a rare section of uplifted oceanic crust.
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The Sierra de Luquillo consists of a series of summits linked by a horseshoe-shaped ridge. Running from west to east, the peaks include El Toro, El Cacique and El Yunque, joined by a ridge known as Cuchilla el Duque to Pico del Oeste and Pico del Este. The mountains were formed by tectonic activity some 37 to 28 million years ago, the island being on the junction between the North American Plate and the Caribbean Plate. The main rock types are pyroclastic rocks, quartzdiorite and contact metamorphic hornfels, with some outcrops of alluvium, basalt and mafic rocks.
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In the Smithton Synclinorium the Togari Group followed with conglomerate from the Sturtian and Marinoan glaciations and dolomite marking the end of Cryogenian and on into the Ediacaran and Cambrian. The Togari group contains greywacke, conglomerate, diamictite, mafic volcanic rocks, and quartz sandstone, and mudstone. The components of the Togari Group are called Forest Conglomerate and Quartzite, Black River Dolomite, Kanunnah subgroup (containing the lavas) and Smithton Dolomite. These rocks are important for determining the boundary between the Cryogenian and Ediacaran periods as they contain volcanics that can be dated and dolomites marking the end of glaciations and marking the period boundary.
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Both terrance shows episodic deposition of volcanic Tonalite- Trondhjemite-Granodiorite TTG. And in TTG yielded an age between 3720 and 3710 Ma, composition of these relatively juvenile igneous rock shows that it is from partial melting of eclogitized mafic material, with high magnesium but low silica content. Partial melting of a subduction-indicating rock shows that the environment was a convergent plate boundary or a subduction zone setting. A thin layer of metasedimentary unit derived mainly from Banded Iron Formation, chert and carbonate rocks is believed to be the dividing unit of 3.8 Ga region and 3.7 region.
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The Watchungs are composed principally of volcanic basalt, which historically has been used in railroad beds and road construction. In addition to this, in many places the mountains are underlain by red and white sandstone which has at times been used in building construction. Mica and calcareous spar often accompany these sandstone beds. An ancient lava front in the Watchungs bearing embedded agate and quartz nodules Due to the volcanic nature of the Watchungs, zeolites, including prehnite, analcime, and stilbite, which form from a reaction of mafic rocks in alkaline environments, can be found along exposed ridge lines.
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The summit of Moel yr Ogof is composed of a brecciated rhyolite, diagnostic of gravitational collapse in a rhyolite dome. Surrounding the crown of the mount is a geological unit consisting of alternating bands, of varying thickness, of pillow basalts and a green/grey sandstone that is of mafic origin, potentially derived from the pillow basalt itself. The pillow basalt is relatively well preserved in places, where devitrification rims clearly outline the individual pillows. It is composed of dark green/black, very fine crystalline, basaltic rock, which has weathered to a dark red/brown colouration due to the presence of iron minerals.
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Cambridge University Press, London, England. The gravel-size portion of the Squantum Member diamictites consists of range from sub-rounded to angular clasts, 5–60 cm (2–24 in) in diameter, to well- rounded clasts 3–8 cm (1.1–3 in) in diameter. They are composed of multicoloured, locally derived felsic and mafic volcanic rocks, granodiorite, quartzite and massive, graded and laminated sandstone and siltstone. The sand- and gravel-sized fraction of the diamictites consist of volcanic, granitic and metasedimentary lithic fragments that have the same composition as the sediments of the Brookline and Dorchester members.
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The basement geology of the Strawberry Mountain Wilderness is a Permian-age ophiolite complex consisting of a sequence of ultramafic, mafic, and silicic igneous rocks, interpreted to have formed as deep crustal rocks near an intra-oceanic island arc system. The sequence is distinctive from other Permo-Triassic ophiolite-type complexes in Western North America by its large volume of silicic intrusive and volcanic rocks. By the mid-Triassic, this complex had been heavily fragmented, uplifted, and overlain by Triassic-age oceanic sediments. All of these Permo-Triassic rocks were incorporated onto the western margin of North America by the mid- Cretaceous.
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While there is relatively little potential for geothermal energy in the High Cascades, there are hot springs along the western edge of the mountain range. The Belknap Hot Spring lies to the southwest of the wilderness area, ejecting water at a rate of per minute with a temperature of . The Mount Washington Wilderness has unknown geothermal potential as there have been few holes deep enough to assess its geothermal resources. Silicic bodies of intrusive rock are typically greater in size than more mafic rock in shallow crust, but geologically young, silicic rock does not occur within the Washington wilderness area.
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This supergroup is a sedimentary-volcanic sequence, in which the sedimentary Schumacherfjellet Formation and Högfonna Formation are intruded by the Grunehogna and Kullen mafic sills (838 Ma). The basaltic lavas of the Straumsnutane Formation (821 Ma) is the uppermost unit within the supergroup. To the east of the Ritscherflya Supergroup, lies the Proterozoic metamorphic terrane of H.U. Sverdrupfjella, which is composed of para- and orthogneisses. The Sør Rondane Mountains are underlain by Late Proterozoic metamorphic rocks of the Teltet-Vengen Group and the Nils Larsen Group gneisses, which are intruded by latest Proterozoic to Early Paleozoic plutonic rocks and dykes.
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Around 200 million years ago in the Triassic, Pangea began to break apart, forming rift valleys. During this period, the Connecticut River Valley began opening as a regional rift, but became a "failed rift" as rifting continued further to the east opening the proto-Atlantic Ocean. Large mafic basalt dikes and flows extruded in the valley, forming the east–west line of the Holyoke Range. The 80-mile-long Hartford Basin and the smaller Deerfield Basin which formed during this time period experience movement along the Connecticut Valley border fault, which bounds the eastern margin of both basins.
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The early history of this region was dominated by volcanic activity, magmatic intrusion and deformation. The Eastern Pilbara Terrane is mostly volcanic in nature, and this volcanic activity occurred in relatively short, and repeated cycles These ultramafic-mafic-felsic cycles which last approximately 10–15 Myr each are accompanied by metamorphism/deformation, and followed by long pauses ( 75 myr) and clastic sediment deposition. Some of the granitic intrusions in the region are subvolcanic, which can be determined through the comparative chemical analysis of the intrusion and associated greenstones. All of these cycles are interpreted to be the result of successive mantle plume events.
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Although the rocks are from different geologic settings, the Montana ringing rocks share significant characteristics with the Pennsylvania diabase ringing rocks. These characteristics include being composed of igneous mafic rock types with high percentages of olivine and pyroxene phenocrysts, having the individual boulders isolated from severe weathering by the formation of well-drained boulder fields, and having similar sounds and surface weathering. The iron content of the olivine pyroxene monzonite (as ferrous oxide) is 7% of the whole rock. As in the Pennsylvania diabase ringing rocks, this point suggests that iron content is not a primary factor in the ringing ability.
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Diorite Orbicular diorite from Corsica (corsite) Diorite classification on QAPF diagram Mineral assemblage of igneous rocks Diorite () is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene. The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite. Diorite is usually grey to dark grey in colour, but it can also be black or bluish-grey, and frequently has a greenish cast. It is distinguished from gabbro on the basis of the composition of the plagioclase species; the plagioclase in diorite is richer in sodium and poorer in calcium.
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The charnockite series includes rocks of many different types, some being felsic and rich in quartz and microcline, others mafic and full of pyroxene and olivine, while there are also intermediate varieties corresponding mineralogically to norites, quartz-norites and diorites. A special feature, recurring in many members of the group, is the presence of a strongly pleochroic, reddish or green orthopyroxene (formerly known as hypersthene). The alkali feldspars in the group are generally perthites, with intergrowths of albite and orthoclase or microcline. Rocks of the charnockite series may be named by adding orthopyroxene to the normal igneous nomenclature (e.g.
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The geology of Nicaragua includes Paleozoic crystalline basement rocks, Mesozoic intrusive igneous rocks and sedimentary rocks spanning the Cretaceous to the Pleistocene. Volcanoes erupted in the Paleogeneand within the last 2.5 million years of the Quaternary, due to the subduction of the Cocos Plate, which drives melting and magma creation. Many of these volcanoes are in the Nicaraguan Depression paralleled by the northwest-trending Middle America Trench which marks the Caribbean-Cocos plate boundary. Almost all the rocks in Nicaragua originated as dominantly felsic continental crust, unlike other areas in the region which include stranded sections of mafic oceanic crust.
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There are 10 active mud volcanoes in the Mariana forearc which can be found along a north to south trend, parallel to the Mariana trench. The material erupted at these mud volcanoes consists primarily of blue and green serpentinite mud which contains fresh and serpentinized peridotite material from the subduction channel. Serpentinite mud is formed as fluid from the down going Pacific plate is released via prehnite-pumpellyite dehydration, greenschist alteration, and blueschist dehydration. This fluid interacts with mafic and ultramafic rocks in the down going Pacific plate and overriding Philippine plate, resulting in the formation of serpentinite mud.
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Monowai has erupted rocks ranging from andesite and basaltic andesite, both mainly around the caldera, to basalt which makes up the bulk of Monowai cone. Dredged samples contain phenocrysts of clinopyroxene, olivine, and plagioclase and define a mainly mafic rock suite, which is unusual for a large caldera. Ultimately, the magmas originate from partial melting of the mantle wedge beneath the Australian Plate and the mixing of water-rich and water-poor melts in a magma chamber. Magma evolution processes occurring in the magma chamber at temperatures of eventually yielded the andesites from a basaltic parental melt.
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Igneous rocks of the Mackenzie Large Igneous Province are generally mafic in composition, including basalt and gabbro. Even though the Mackenzie Large Igneous Province is classified as a large igneous province like other extremely large accumulations of igneous rocks on Earth, it is much larger than large igneous province standards. The standard size classification for large igneous provinces is a minimum areal extent of . However, the Mackenzie dike swarm itself occupies an area of at least , making the Mackenzie Large Igneous Province larger than the Ontong Java Plateau (in the southwestern Pacific Ocean) and the U.S. state of Alaska.
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Like most large igneous provinces, the Mackenzie Large Igneous Province has its origins in a mantle plume--an upwelling zone of abnormally hot rock within the Earth's mantle. As the head of the Mackenzie plume encountered the Earth's lithosphere, it spread out and melted catastrophically to form large volumes of basaltic magma. This resulted in the creation of a stationary volcanic zone west of Victoria Island that experienced considerable volcanism known as the Mackenzie hotspot. Evidence for the Mackenzie hotspot include the existence of the giant mafic Mackenzie dike swarm because of its fanning pattern adjacent to the Muskox intrusion.
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Talat Ahmad has over 65 research publications to his credit. He has supervised several M. Phil and PhD research studies at the University of Delhi and the Research School of Earth Sciences, Australian National University, Canberra, Australia. He has been working on various sponsored projects, including Geochemical, Isotopic and Geochronological characterisation of Granotoids from the Central Indian Tectonic Zones (CITZ) and Central Indian Shear Zones (CISZ)-Constraints on Pre-cambrian Crystal Evolution, funded by Indo-Russian, ILTP Project, and Proterozoic mafic magmatism in the Central Indian Tectonic Zone (CITZ): elemental and isotopic constraints on crystal evolution and geodynamics.
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The Evje og Hornnes municipality is situated at the southwestern margin of the Baltic Shield, the exposed section of the East European craton. Rocks in the area are dominated by different types of precambrian gneis and a large metagabbro body stretching into the neighboring Iveland municipality. During the final stages of Sveconorwegian (0,9–1,1 Ga) orogeny, a large pluton of granitic/monzonitic composition was emplaced in the northern part of the municipality and is assumed to have a relationship with the thousands of pegmatite veins in the Evje-Iveland area. Earlier during the Sveconorwegian orogeny, mafic rocks (gabbro-diorite) were emplaced.
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The Temagami area also contains some pillow lava about 2 billion years old, indicating that great submarine volcanoes existed during the early stages of the formation of the Earth's crust. The northeast arm of Lake Temagami is underlain by a strong fault zone of sheared felsic to intermediate metavolcanic rocks that is approximately wide. This fault zone, known as the Northeast Arm Deformation Zone, and the associated metavolcanic rocks are associated with the Temagami Greenstone Belt, an Archean greenstone belt characterized by felsic-mafic volcanic rocks. Lake Temagami and its surrounding lakes provide endless opportunities for canoe camping.
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Shield volcanoes near Mazama feature lava flows made of agglutinated mafic andesite, which form sheets about thick, as well as more deposits from more viscous andesite and dacite magma that reach thicknesses up to . Many of these deposits (both dacitic and andesitic) contain undercooled, crystal-poor segments of andesite, including at Mount Scott and Phantom Cone. Lava and ice interactions are suggested by exposures of glassy breccia in Mazama's caldera, and lava flows cover glaciated lava deposits. About 70,000 years ago, several silicic (rich in silicon dioxide), explosive eruptions occurred, including a significant event at Pumice Castle on the eastern wall of Mazama.
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One volcanic vent, situated high on the slope, produced a large ʻaʻā flow, dubbed the Kaʻūpūlehu flow, that reached the ocean as two distinct lobes. On its way down, it overran a village and a valuable fishing pond. There is a local legend that after the failure of several offerings of animals and other items to the gods, the flow was finally stopped when Kamehameha I threw a lock of his own hair into the fire. The Ka'ūpūlehu flow is also known for the particularly large quantity of mafic and ultramafic xenoliths that came up with it.
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The authors refer to their experience from watching and researching the Gjálp eruption from 1996 which has had many similarities to the Helgafell formation. At Helgafell next an edifice was formed about 300 m high in an ice vault, meltwater drained away very fast through subglacial channels so that the explosive activity continued to the end, which seems to have been after some days. This explains the fact, that Helgafell is next to overall made from mafic hyaloclastite, whereas most other researched smaller subglacial volcanoes showed a basis of pillow lavas. Of these and some small intrusions, the researchers just found minimal quantities.
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This region has a high vent density, with many mafic (rich in magnesium and iron) volcanoes of Pleistocene to Holocene age, such as Hoodoo. While Hoodoo has an intact summit crater that was blocked from erosion by glaciers, it has an irregular topography, giving it an open appearance. A ski area, also named Hoodoo, is located on the northwest through northeast flanks of the cone, and includes five chairlifts. Other recreational activities popular in the area include snowshoeing and snowmobiling during the winter, and fishing, hiking, camping, mountain biking, windsurfing, and water skiing popular during the summer season.
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Magmas that have been so altered are said to be "evolved" to distinguish them from "primitive" magmas that more closely resemble the composition of their mantle source. (See igneous differentiation and fractional crystallization.) More highly evolved magmas are usually felsic, that is enriched in silica, volatiles, and other light elements compared to iron- and magnesium-rich (mafic) primitive magmas. The degree and extent to which magmas evolve over time is an indication of a planet's level of internal heat and tectonic activity. The Earth's continental crust is made up of evolved granitic rocks that developed through many episodes of magmatic reprocessing.
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First, basaltic andesite, which is the typical calc-alkaline volcanic arc basalt, mixes with basalt derived from melting of sub-crustal basalt cumulates; then the resulting mixture interacts with rhyodacite melts derived from Proterozoic crustal material. The initial melt contributes most of the material in mafic inclusions and the rhyodacite contributes most of the dacite material. The principal magma basin appears to be located at depth, although some petrological traits of the erupted rocks indicate a secondary area of petrogenesis at of depth. Fractional crystallization and partial melting are involved in the formation of Taapaca magmas.
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Zimbabwe and Kaapvaal Cratons SW end of the 550 km long 350px upright The geology of Zimbabwe in southern Africa is centered on the Zimbabwe Craton, a core of Archean basement composed in the main of granitoids, schist and gneisses. It also incorporates greenstone belts comprising mafic, ultramafic and felsic volcanics which are associated with epiclastic sediments and iron formations. The craton is overlain in the north, northwest and east by Proterozoic and Phanerozoic sedimentary basins whilst to the northwest are the rocks of the Magondi Supergroup. Northwards is the Zambezi Belt and to the east the Mozambique Belt.
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In California, volcanoes like Lassen Peak and Mount Shasta occur among rings of mafic (rich in magnesium and iron) shield volcanoes and volcanic fields such as the Medicine Lake Volcano. Big Cave lies at the northern end of a belt of late, Quaternary volcanoes moving north from Lassen Peak. It is a small shield volcano, likely formed during the Holocene epoch, though scientists from the United States Geological Survey are unsure. It could also be from the late Pleistocene epoch; M. A. Clynne thought it may be of similar age to the nearby Cinder Butte volcano, at 38,000 ± 7,000 years.
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Plumes also tend to create warping of the crust, weaken it thermally so that it is easier to intrude magma and create space to host the intrusions. Geochemical evidence supports the hypothesis that some intrusions result from plume magmatism. In particular, the Noril'sk-Talnakh intrusions are considered to be created by plume magmatism, and other large intrusions have been suggested as created by mantle plumes. However, the story is not so simple, because most ultramafic-mafic layered intrusions also correlate with craton margins, perhaps because they are exhumed more efficiently in cratonic margins because of faulting and subsequent orogeny.
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The hill contains a slender, chilled margin of fine-grained basalt with most of the mass of the intrusion being made up of picrite and dolerite. Volcanic rocks on the hill are predominantly mafic. Minerals, and as well as volcanic material, found on the hill are follows: analcime, apophyllite, basanite, basalt, trachyte, aragonite, barite, calcite, chabazite, chlorite, heulandite, ilmenite, laumontite, leucitite, limburgite, montmorillonite, natrolite, nephelinite, olivine, pectolite, pyrite, phillipsite, prehnite, quartz, rhyolite, siderite, trachybasalt, trachyandesite, tuff and high level intrusives; rare volcaniclastic sediments.Raymond, O.L., Liu, S., Gallagher, R., Zhang, W., Highet, L.M. Surface Geology of Australia 1:1 million scale dataset 2012 edition.
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Others, such as pyrope's high specific gravity, may be of little use when studying a small crystal embedded in a matrix of other silicate minerals. In these cases, mineral association with other mafic and ultramafic minerals may be the best indication that the garnet you are studying is pyrope. In petrographic thin section, the most distinguishing features of pyrope are those shared with the other common garnets: high relief and isotropy. Garnets tend to be less strongly coloured than other silicate minerals in thin section, although pyrope may show a pale pinkish-purple hue in plane-polarized light.
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Mont Yamaska is composed of igneous rock and hornfels. The igneous rock is mostly mafic with much gabbro, essexite, and a titanium-rich pyroxenite. Mont Yamaska might be the deep extension of a vastly eroded ancient volcanic complex, which was probably active about 125 million years ago.A Hundred-Million Year History of the Corner Rise and New England Seamounts Retrieved on 2007-08-01 The mountain was created when the North American Plate moved westward over the New England hotspot, along with the other mountains of the Monteregian Hills that form part of the Great Meteor hotspot track.
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Larger outbreaks of lava have also been observed on Io. For example, the leading edge of the Prometheus flow moved between Voyager in 1979 and the first Galileo observations in 1996. A major eruption in 1997 produced more than of fresh lava and flooded the floor of the adjacent Pillan Patera. Analysis of the Voyager images led scientists to believe that these flows were composed mostly of various compounds of molten sulfur. However, subsequent Earth-based infrared studies and measurements from the Galileo spacecraft indicate that these flows are composed of basaltic lava with mafic to ultramafic compositions.
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Other processes, such as volcanic activity and geologic faulting in which the earth cracks open also contributed to the formation of these mountains. Over millions of years, these enormous mountains were gradually eroded to the land we know today in Temagami. While Rabbit Lake is a fairly quiet lake dotted with cottages, the forest is continually logged and the threat of mining is looming ever closer with the discovery of kimberlite, a volcanic rock notable as a diamond indicator.Diamond Discoveries This in turn forms part of the Temagami Greenstone Belt, an Archean greenstone belt characterized by felsic-mafic volcanic rocks.
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The deposits also contain large amounts of quartz, especially pyroxene-rimmed quartz crystals, with sparse appearance of olivine and calcic-plagioclase xenocrysts. At dome E, the penultimate dome to be produced, non-bedded deposits with fine, granular pieces to blocks with lengths of up to occur, and many of the larger blocks have internal fractures. Domes D, C, and A have compositions that are extremely similar to dome F; dome B, too, is similar, but also has pumice deposits and mafic inclusions. At dome E and dome D, there are also talus blocks as large as in length.
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The expressions of a thick pile of dominantly mafic, bimodal volcanics and the Tibbit Hill volcanics in the Humber Zone of the Quebec Appalachians are believed to be related to the formation of the Ottawa-Bonnechere Graben. The precise age of these volcanics is unknown but they are either early Cambrian and late Precambrian. This volcanism was probably coeval with the emplacement of the Grenville dike swarm. Minor but significant igneous activity occurred during the Mesozoic era, including kimberlite emplacement during the Jurassic period, and the development of alkalic intrusions along the Ottawa-Bonnechere Graben and elsewhere in Ontario.
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Subsequently, lava flows of mafic to trachydacitic composition were emplaced, in part on top of the earlier ignimbrites. Between 9.09–1.59 million years ago activity was continuous and dominated by lava flows of andesitic to dacitic composition, which constructed the main Antofalla volcano and the surrounding vents. Small felsic eruptions generating lava domes and ignimbrites concluded this activity, with the ignimbrite in Quebrada de las Cuevas dated to 1.59 ± 0.08 million years ago. Other volcanic units attributed to this volcanic complex are the Aguas Calientes basalt, the Los Patos ignimbrite of lower Pliocene age and the Tambería Ignimbrite.
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Greenstones, aside from containing basalts, also give rise to several types of metamorphic rocks which are used synonymously with 'metabasalt' et cetera; greenschist, whiteschist and blueschist are all terms spawned from the study of greenstone belts. The West African early Proterozoic greenstone belts are similar to the Archean greenstone belts. These similarities include a decrease in the amount of ultramafic and mafic rocks as you move up the stratigraphic column, in addition to an increase in pyroclastics, felsic and/or andesite rocks. Also, the rock successions tend to have clastics in the upper portion and tholeiitic suites in the lower.
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The Elephant Rocks, for which Elephant Rocks State Park is named, is a pile of residual boulders of weathered Graniteville Granite. It is a medium- to coarse-grained, muscovite- biotite alkali granite that, on the average, consists of 55 percent alkali feldspar, 40 percent quartz, and less than 5 percent mafic minerals. The Graniteville Granite is a pluton formed 1.4 billion years ago in the Proterozoic by the cooling of magma that intruded into the volcanic strata and country rock associated with a collapsed caldera. Nearly vertical fractures formed in the stone as it cooled, and uplift of the granite enhanced the fracturing.
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Trachyte is the most common rock on Mount Takahe, phonolite being less common. Basanite, hawaiite, and mugearite are uncommon, but the occurrence of benmoreite and pantellerite has been reported, and some rocks have been classified as andesites. Hawaiite occurs exclusively in the older outcrops, basanite only in parasitic vents and mugearite only on the lower sector of the volcano. Despite this, most of the volcano is believed to consist of mafic rocks with only about 10–15% of felsic rocks, as the upper visible portion of the volcano could be resting on a much larger buried base.
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Igneous samples from Northeast Syrtis could provide four key time for Martian geology history, including (1) the timing of Isidis impact event, (2) the timing of emplacement of olivine-rich unit, (3) the timing of dark-toned mafic cap rock, (4) the timing of Syrtis lava flows, which would fundamentally improve human knowledge of early Mars and the early history of solar system, such as the late-heavy bombardment. This region exposes the largest high-olivine abundance rocks on Mars. The origin of high-olivine rock is still in debate. Impact cumulates or olivine-rich lava are two leading hypotheses.
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The Aleutian island arc crust in Alaska is ~25 km thick, and has a volume of ~2300 km3 per kilometer of the arc. Seismic reflection and refraction surveys indicate that the composition of the Aleutian island arc is not similar to the composition of continental crust. Relatively high p-wave velocities indicate mafic rocks are present and this is verified in the geology of the crust. In the upper crust, there is ~6 km of basaltic andesite, while the middle crust is composed of 5 km-thick mid-ocean ridge basalt (MORB), and 19 km- thick tholeiitic residue in the lower crust.
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The Itcha Range as seen from the south During the mafic capping stage, basanite, alkali olivine basalt and hawaiite erupted mainly from small parasitic cones, tuff rings and fissures in the eastern half of the shield. Eruptions occurred subglacially, subaqueously and/or subaerially as shown by a wide range in the degree of vesicularity, freshness and glass content of the lavas. In most cases, each parasitic cone produced three or four lava flows from breaches in the cone walls. These were erupted as pāhoehoe and ʻaʻā, but the tops of the lava flows are commonly missing due to erosion.
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Activity at Incapillo commenced shortly after the end of the Maricunga Belt volcanism and occurred first at Monte Pissis between 6.5 and 3.5mya. Later volcanism occurred south of Incapillo 4.7±0.5mya, at Sierra de Veladero 5.6±1–3.6±0.5mya, and in the region of Cerro Bonete Chico 5.2±0.6–3.5±0.1mya. Some of the 32mya Pircas Negras mafic andesites appear to be associated with the Incapillo volcanic complex. These rocks form the last pulse of the Pircas Negras volcanism. Specific ages of the Pircas Negras flows in the Incapillo region include 4.7±0.5mya, 3.2±0.3mya and 1.9±0.2mya.
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The Barberton greenstone belt (BGB) is located in the Kapvaal craton of southeastern Africa. It characterizes one of the most well-preserved and oldest pieces of continental crust today by containing rocks in the Barberton Granite Greenstone Terrain (3.55–3.22 Ga). The BGB is a small, cusp-shaped succession of volcanic and sedimentary rocks, surrounded on all sides by granitoid plutons which range in age from >3547 to <3225 Ma. It is commonly known as the type locality of the ultramafic, extrusive volcanic rock, the komatiite. Greenstone belts are geologic regions generally composed of mafic to ultramafic volcanic sequences that have undergone metamorphism.
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The degree of partial melting is critical to determination of the characteristics of the magma it produces, and the likelihood that a melt forms reflects the degrees to which incompatible and compatible elements are involved. Incompatible elements commonly include potassium, barium, caesium, and rubidium. Rock types produced by small degrees of partial melting in the Earth's mantle are typically alkaline (Ca, Na), potassic (K) or peralkaline (in which the aluminium to silica ratio is high). Typically, primitive melts of this composition form lamprophyre, lamproite, kimberlite and sometimes nepheline-bearing mafic rocks such as alkali basalts and essexite gabbros or even carbonatite.
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As inferred from relict structures and textures, the Brahma Schist is composed of mafic to felsic-composition metavolcanic rocks. The Rama Schist consists of massive, fine-grained quartzofeldspathic schist and gneiss that likely are probable felsic metavolcanic rocks. On the basis of the presence of relict pillow structures, interlayering of metavolcanic strata, and the large volumes of metavolcanic rocks, the Brahma and Rama schists are interpreted to consist of metamorphosed, volcanic island-arc and associated submarine volcanic rocks. These metavolcanic rocks are locally overlain by the metamorphosed submarine sedimentary rocks of the Vishnu Schist that are interpreted to have accumulated in oceanic trenches.
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Initially, they were defined as spherical masses, which may or may not be spherulites, that are observed on the weathering surfaces of some basalts and diabases. In some modern literature, the term variole is defined as a type of spherulite that occurs in a mafic rock. However, because several different mechanisms can produce these small-scale, light-colored, globular to spherical structures, a specific set of varioles may or may not be spherulites that are composed of radiating crystals of either plagioclase or pyroxene. As a result, it is recommended that the term variole should be retained as originally defined.
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The variety of mafic igneous rocks that contain varioles are, with rare exceptions, no longer classified as variolites, which is not recommended for usage. Instead, they are designated using the modifier variolitic in conjunction with the major lithology. The major varieties of variolites are variolitic basalts, variolitic pillow lavas and variolitic komatiites. Variolitic pillow lavas, that have been previously identified as variolites and also classified as spilites, are found in the Durance, France; on Mont Genvre, France; in Devonian rocks of Germany; and as cobbles on the beaches of the Strait of Juan de Fuca along the northern edge of the Olympic Peninsula.
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Other rock alterations include small veins of quartz and epidote, vesicles filled with quartz, calcite and chlorite, extensive replacement of volcanic rock by silica or calcite, and calcite precipitation in extension fractures. Outcrops of silicified mafic pillow lava are found along and west of the Ontario Northland Railway, east of the Big Dan Shear Zone and adjacent to Outlet Bay and Boot Bay of Net Lake. This form of alteration occurs in deformation zones and is the product of low temperature seawater alteration. Volcanic rock replaced by carbonate is commonly found in the Northeast Arm Deformation Zone, the Link Lake Shear Zone and in the Net Lake-Vermilion Lake Deformation Zone.
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Geologists have interpreted the metasedimentary belts between the East Sahara Craton and the Red Sea fold and thrust belt as a rifting zone, related to the formation of an ocean in the Neoproterozoic. The Jebel Rahib Belt, situated in the northwest, contains deformed basic and ultrabasic igneous rocks and thick layers of carbonaceous metasediments, formed at the time of the Pan-African orogeny. This time constraint for deformation and low-grade metamorphism comes from granitoids formed after the orogeny, dated to 570 million years ago. Dense, mafic oceanic crust formed in the Jebel Rahib rift as evidenced by an ophiolite assemblage that includes ultramafic rocks, pyroxenite, gabbro, chert and pillow lava.
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Eswatini is the only country entirely underlain by the Kaapvaal Craton. Eswatini is built on 3.6 to 2.5 billion year old Archean continental crust that forms the Kaapvaal Craton spanning into South Africa, northern Lesotho, western Mozambique, Botswana and southern Zimbabwe. The Precambrian rocks of Eswatini from this period are primarily gneiss and granite, formed between 3.4 and 2.6 billion years ago, based on rubidium-strontium dating analysis in 1976. The two rock units of the basement in Eswatini are the Ancient Gneiss Complex and 20 kilometer thick mafic and ultramafic volcanic rocks of the Paleoarchean Swaziland Supergroup includes tonalite gneiss, ironstone, conglomerate and other sediments.
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Obduction is the overthrusting of continental crust by oceanic crust or mantle rocks at a convergent plate boundary, such as closing of an ocean or a mountain building episode. This process is uncommon because the denser oceanic lithosphere usually subducts underneath the less dense continental plate. Obduction occurs where a fragment of continental crust is caught in a subduction zone with resulting overthrusting of oceanic mafic and ultramafic rocks from the mantle onto the continental crust. Obduction often occurs where a small tectonic plate is caught between two larger plates, with the crust (both island arc and oceanic) welding onto an adjacent continent as a new terrane.
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Geological map of Skye Basal quartzite of the Eriboll Group from the Ord Window dolomites forming a limestone pavement on Bheinn Shuardail Cross- bedded Jurassic sandstones of the Bearreraig Sandstone Formation near Glasnakille, Strathaird Duirinish peninsula Mafic dyke near Broadford cutting Durness Group dolomite The Kilt Rock with a columnar jointed dolerite sill above Jurassic sandstones of the Valtos Sandstone Formation The geology of the Isle of Skye in Scotland is highly varied and the island's landscape reflects changes in the underlying nature of the rocks. A wide range of rock types are exposed on the island, sedimentary, metamorphic and igneous, ranging in age from the Archaean through to the Quaternary.
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Heavy minerals (dark) in a quartz beach sand (Chennai, India). If the abundance of elements in Earth's crust is compared for titanium, zirconium and hafnium, the abundance decreases with increase of atomic mass. Titanium is the seventh most abundant metal in Earth's crust and has an abundance of 6320 ppm, while zirconium has an abundance of 162 ppm and hafnium has only an abundance of 3 ppm. All three stable elements occur in heavy mineral sands ore deposits, which are placer deposits formed, most usually in beach environments, by concentration due to the specific gravity of the mineral grains of erosion material from mafic and ultramafic rock.
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Spatter cones and spatter ramparts are typically formed by lava fountaining associated with mafic, highly fluid lavas, such as those erupted in the Hawaiian Islands. As blobs of molten lava, spatter, are erupted into the air by a lava fountain, they can lack the time needed to cool completely before hitting the ground. Consequently, the spatter are not fully solid, like taffy, as they land and they bind to the underlying spatter as both often slowly ooze down the side of the cone. As a result, the spatter builds up a cone that is composed of spatter either agglutinated or welded to each other.
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Lava flows represent a major volcanic terrain on Io. Analysis of the Voyager images led scientists to believe that these flows were composed mostly of various compounds of molten sulfur. However, subsequent Earth-based infrared studies and measurements from the Galileo spacecraft indicate that these flows are composed of basaltic lava with mafic to ultramafic compositions. This conclusion is based on temperature measurements of Io's "hotspots", or thermal-emission locations, which suggest temperatures of at least 1,300 K and some as high as 1,600 K. Initial estimates suggesting eruption temperatures approaching 2,000 K have since proven to be overestimates because the wrong thermal models were used to model the temperatures.
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Hot Lake is a hypersaline, meromictic lake located in extreme northern Okanogan County, Washington near Oroville, Washington. Occupying a small, glacially-carved basin surrounded by mafic magnesian rocks, dolomites, and shales containing deposits of pyrite and pyrrholite minerals, Hot Lake is unusual among hypersaline lakes in that it is dominated by magnesium and sulfate as its major ions. Because of its mineralogy, Hot Lake was mined for epsomite, initially by the Stewart-Calvert Company during World War I, when the importation of epsomite from Germany was suspended. Major flora growing within the lake include Ruppia maritima and Chara, and the dominant fauna are the brine shrimp Artemia salina and Branchinecta campestris.
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The darker bands have relatively more mafic minerals (those containing more magnesium and iron). The lighter bands contain relatively more felsic minerals (silicate minerals, containing more of the lighter elements, such as silicon, oxygen, aluminium, sodium, and potassium). A common cause of the banding is the subjection of the protolith (the original rock material that undergoes metamorphism) to extreme shearing force, a sliding force similar to the pushing of the top of a deck of cards in one direction, and the bottom of the deck in the other direction. These forces stretch out the rock like a plastic, and the original material is spread out into sheets.
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The full extent of the Sudbury Basin is long, wide and deep, although the modern ground surface is much shallower. The main units characterizing the Sudbury Structure can be subdivided into three groups: the Sudbury Igneous Complex (SIC), the Whitewater Group, and footwall brecciated country rocks that include offset dikes and the Sub layer. The SIC is believed to be a stratified impact melt sheet composed from the base up of sub layer norite, mafic norite, felsic norite, quartz gabbro, and granophyre. The Whitewater Group consists of a suevite and sedimentary package composed of the Onaping (fallback breccias), Onwatin, and Chelmsford Formations in stratigraphic succession.
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Beerenberg, a 2.27 kilometer tall volcano rises on the north end of the island, covered in more than 20 glaciers. Jan Mayen is made up of basalt flows and pyroclastic flow related mafic deposits. The two most recent eruptions were in 1970 and 1985, although the Central Crater and Egg Island craters on the southern side of the mountain have continuous fumarole activity. Tectonic geologists have identified Jan Mayen as a microcontinent, which has experienced significant deformation around its boundaries due to sea-floor spreading and the formation of new plate boundaries since the Paleocene, with full separation as a microcontinent in the Oligocene.
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The Three Sisters form the centerpiece of a region of closely grouped volcanic peaks, an exception to the typical spacing between volcanoes elsewhere in the Cascades. This vicinity is among the most active volcanic areas in the Cascades and one of the most densely populated volcanic centers in the world, as well as the second largest volcanic field of silicic rock within the Quaternary Cascades. The area from the Three Sisters to Broken Top and Mount Bachelor features at least 50 eruptive vents for rhyolitic and rhyodacitic lava. East of Broken Top, the Tumalo volcanic center, an area of andesitic and mafic scoria cones, features similarly rhyolitic and rhyodacitic lava deposits.
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Olivine in a peridotite weathering to iddingsite within a mantle xenolith Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.
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Warionia saharae is an endemic of Morocco between Tamanar, Ifni, Erfoud and Figuig, and of Algeria, in the Naâma Province and the Béni Ounif District. It grows on slopes of the High Atlas, Anti-Atlas and Saharian Atlas, along the coast of southern Morocco, and in the desert, on mafic and siliceous rock, at altitudes between sea level and 1300 m. At Ifni it was found growing together with Euphorbia echinus, E. obtusifolia and Senecio anteuphorbium. The species loses its leaves when seasonal water availability drops below a threshold in summer, but in cultivation it keeps its leaves as long as it is watered adequately.
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The definition of LIP has been expanded and refined, and is still a work in progress. LIP is now frequently also used to describe voluminous areas of, not just mafic, but all types of igneous rocks. Sub-categorization of LIPs into large volcanic provinces (LVP) and large plutonic provinces (LPP), and including rocks produced by normal plate tectonic processes, has been proposed but are not generally accepted. Some LIPs are geographically intact, such as the basaltic Deccan Traps in India, while others have been fragmented and separated by plate movements, like the Central Atlantic Magmatic Province (CAMP)—parts of which are found in Brazil, eastern North America, and north-western Africa.
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The hydrological conditions in these areas likely were controlled by relatively uniform ice thickness and gentle topography. The seconed type of volcano-ice interaction is located only to the east, south and southwest of the Tanzilla Plateau, in the Cassiar Mountains, Skeena Mountains and in the Boundary Ranges. Volcanic activity in these locations is also largely mafic in composition, but the extensive elevations of these areas had a much more impressive influence on glaciation and subglacial volcanism. High altitude glaciation took over when the Cordilleran Ice Sheet was not present and even when buried by the Cordilleran Ice Sheet, basal ice movement was strongly influenced by the deep, pre-glacial drainages.
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The Pacific is a broad ocean basin (unlike the narrow Atlantic Ocean) and extends over a width of between New Guinea and Peru. The andesite line, a zone of intense volcanic and seismic activity, is a major regional distinction in the Pacific. The petrologic boundary separates the deeper mafic igneous rock of the Central Pacific Basin from the partially submerged continental areas of felsic igneous rock on its margins. The andesite line follows the western edge of the islands off California and passes south of the Aleutian arc, along the eastern edge of the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands, the Solomon Islands, and New Zealand's North Island.
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Lau Basin volcanics are mainly andesites and dacites that were erupted 6.4 to 9.0 Ma. Most mafic rocks found are 55% SiO2 basaltic andesites. The whole basin floor is mostly composed of MORB-like rocks, but the westmost 80~120 km of the basin floor contains a mixture of MORB, transitional and arc- like basalts. This western region has a different composition because it was formed by extension and rifting between the Lau and Tonga ridges before seafloor spreading started. The grabens in this region was then filled by fresh magma from a mantle source that is different from the mantle source for CLSC/ELSC.
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Tectonic processes also took place, such as two phases of east-west compression; the first was in the middle Miocene and the second began 7 million years ago. Volcanism in the southern Puna region initiated about 8 million years ago and took place in several stages, which were characterized by the emplacement of lava domes and of ignimbrites such as the 4.0 - 3.7 million years old Laguna Amarga-Laguna Verde ignimbrites. Some of the domes are located close to the border with Chile in the Ojos del Salado and Nevado Tres Cruces area. Later there also were mafic eruptions, which generated lava flows in the Carachipampa and Laguna de Purulla area.
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For example, volcanoes in Mexico and western North America are mostly in volcanic belts, such as the Trans-Mexican Volcanic Belt that extends 900 km from west to east across central-southern Mexico and the Northern Cordilleran Volcanic Province in western Canada. The deeply deformed and eroded remnants of ancient volcanic belts are found in volcanically inactive regions such as the Canadian Shield. It contains over 150 volcanic belts (now deformed and eroded down to nearly flat plains) that range from 600 to 1200 million years old. These are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that form what are known as greenstone belts.
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Big Dan is situated in the Temagami Greenstone Belt, a 2,736 million year old sequence of metamorphosed igneous and sedimentary rocks that forms part of the much larger Superior craton. The belt is exposed through the Huronian Supergroup and represents an isolated southern exposure of the Abitibi Subprovince. Rock waste adjacent to the adit open cut Volcanic activity in the Temagami Greenstone Belt spanned from 2,736 to 2,687 million years ago, indicating that it was a zone of active volcanism for at least 49 million years. The Younger Volcanic Complex, a unit of the Temagami Greenstone Belt made of mostly mafic volcanic rocks, is the main volcanic complex at Big Dan.
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Fahrig (1987) proposed that the Mackenzie plume impact resulted in the emplacement of a triple junction that had a large mafic dike swarm on every rift arm. Two of the first arms formed the Poseidon Ocean basin and the third arm failed thus forming an aulacogen. This tectonic setting suggestion can be comparable with the early volcano- tectonic evolution of the Yellowstone hotspot, which developed two arms instead of three, followed by failure of both arms. At the Mackenzie hotspot, rifting is considered to have been passive and to have taken place in the crust above the hotspot that should have been weakened by the Mackenzie plume.
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It represents one of the largest large igneous provinces in Canada, consisting of the Natkusiak flood basalts on Victoria Island, the Coronation sills on the southern shore of the Coronation Gulf and the large Franklin dike swarm, which extends for more than across the Canadian Arctic Archipelago and northwestern Greenland.Ar40-Ar39 Dating of the Lasard River Mafic Dykes, and Implications for the Focus of the 0.72 Ga Franklin Large Igneous Province of Northern Canada The Franklin Large Igneous Province covers an area of more than .Igneous rock associations in Canada 3. Large Igneous Provinces (LIPs) in Canada and adjacent regions: 3 Ga to Present.
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A vertical quartz vein exposed in Gwen Resources' test pit Beanland is situated in the Temagami Greenstone Belt, a 2,736 million year old sequence of metamorphosed igneous and sedimentary rocks that forms part of the much larger Superior craton. The belt is exposed through the Huronian Supergroup and represents an isolated southern exposure of the Abitibi Subprovince. Volcanic activity in the Temagami Greenstone Belt spanned from 2,736 to 2,687 million years ago, indicating that it was a zone of active volcanism for at least 49 million years. The Younger Volcanic Complex, a unit of the Temagami Greenstone Belt made of mostly mafic volcanic rocks, is the main volcanic complex at Beanland.
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The Sand Mountain Field is located from a population of roughly 500,000 people. It is close to a major transportation corridor from central Oregon to the Willamette Valley as well as a popular ski area, and future eruptions could have "substantial societal consequences" according to Deligne et al. (2016). Lava flows from an eruption in the surrounding Central Oregon volcanic field could reach highways, but most mafic volcanism in the region is unlikely to threaten transportation given the small number of local roads. Tephra from eruptions at Sand Mountain could reach more than from the vent, and if lava flows reached forested regions they could initiate forest fires.
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The only eruption recognized to have produced ash flow tuff occurred in late Pleistocene time, and this eruption was too small to account for formation of the caldera. Later conclusions were that Medicine Lake caldera formed by collapse in response to repeated extrusions of mostly mafic lava beginning early in the history of the volcano (perhaps in a manner similar to the formation of Kilauea caldera in Hawaii). Several small differentiated magma bodies may have been fed by and interspersed among a plexus of dikes and sills. Late Holocene andesitic to rhyolitic lavas were derived by fractionation, assimilation, and mixing from high alumina basalt parental magma.
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Laxfordian event Laxford is in the region of the Lewisian gneiss complex, deformed by Moine Thrust, which occurred during the Caledonian Orogeny. To the south are Scourian high-grade metamorphic rocks, some 3,000 million years old, intruded with undeformed Scourie dykes 2,400 million years ago whereas to the north are lower-grade metamorphic rocks, which were later deformed and metamorphosed during the Laxfordian orogeny. At Laxford, layers of pink granite and pegmatite intruded into hot gneiss about 1,750 million years ago. Alternating layers of black mafic gneiss and grey felsic gneiss are to be seen, cut across by steeply dipping sheets of granite and pegmatite.
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Temperature measurements from Galileo's Solid-State Imager (SSI) and Near-Infrared Mapping Spectrometer (NIMS) revealed numerous hot spots with high-temperature components ranging from at least to a maximum of , like at the Pillan Patera eruption in 1997. Initial estimates during the course of the Galileo mission suggesting eruption temperatures approaching have since proven to be overestimates because the wrong thermal models were used to calculate the temperatures. Spectral observations of Io's dark material suggested the presence of orthopyroxenes, such as enstatite, magnesium-rich silicate minerals common in mafic and ultramafic basalt. This dark material is seen in volcanic pits, fresh lava flows, and pyroclastic deposits surrounding recent, explosive volcanic eruptions.
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The seismic data is not sufficient to determine the composition of the mantle. Observations of rocks exposed on the surface and other evidence reveal that the upper mantle are mafic minerals olivine and pyroxene and it has a density of about Upper mantle material which has come up onto the surface is made up of about 55% olivine and 35% pyroxene and 5 to 10% of calcium oxide and aluminum oxide. The upper mantle is dominantly peridotite, composed primarily of variable proportions of the minerals olivine, clinopyroxene, orthopyroxene, and an aluminous phase. The aluminous phase is plagioclase in the uppermost mantle, then spinel, and then garnet below ~100 km.
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The primary rock type on the surface of Mars is basalt, a fine-grained igneous rock made up mostly of the mafic silicate minerals olivine, pyroxene, and plagioclase feldspar. When exposed to water and atmospheric gases, these minerals chemically weather into new (secondary) minerals, some of which may incorporate water into their crystalline structures, either as H2O or as hydroxyl (OH). Examples of hydrated (or hydroxylated) minerals include the iron hydroxide goethite (a common component of terrestrial soils); the evaporite minerals gypsum and kieserite; opaline silica; and phyllosilicates (also called clay minerals), such as kaolinite and montmorillonite. All of these minerals have been detected on Mars.
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The first oceanic core complexes described were identified in the Atlantic Ocean.; Since then numerous such structures have been identified primarily in oceanic lithosphere formed at intermediate, slow- and ultra-slow spreading mid-ocean ridges, as well as back-arc basins.; Examples include 10-1000 square km expanses of ocean floor and therefore of the oceanic lithosphere, particularly along the Mid-Atlantic Ridge and the Southwest Indian Ridge. Some of these structures have been drilled and sampled, showing that the footwall can be composed of both mafic plutonic and ultramafic rocks (gabbro and peridotite primarily, in addition to diabase), and a thin shear zone that includes hydrous phyllosilicates.
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Originally, the Granada ignimbrite was also considered to be a product of an earlier eruption of the Vilama caldera; later research indicated that it has its own eruptive centre at Abra Granada that is unrelated to Vilama. According to this older theory of caldera history, the Granada ignimbrite was the first stage of caldera formation, with the second stage generating the Vilama ignimbrite proper. This theory also envisaged two later stages of activity, the first linked to the Cerro Morado mafic volcanics and the Salle and Ceja Grande ignimbrites, while the fourth produced the Bonanza ignimbrite from the Coruto caldera as well as additional volcanoes including Cerro Zapaleri.
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Mafic inclusions occur in some eruption products. The basement of the region is formed by various formations of Precambrian to Tertiary age, some of which crop out around the volcano. This basement is cut by various faults, which mark an uplift that forms the Creston Alto de La Aguada east of Chimpa volcano, as well as the Calama-Olacapato-El Toro lineament and associated faults which runs south of the Chimpa volcano and has localized the formation of volcanoes along its path and also influenced the activity of Chimpa. Cerro Rumio is another volcano which crops out south of Chimpa and is in part buried by Chimpa's deposits.
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Mount Washington is also part of the Sisters Reach subsegment, which extends for and contains at least 466 volcanoes that were active during the Quaternary. Washington represents one of 30 mafic (rich in magnesium and iron) stratovolcanoes and shield volcanoes in the group, which include Pleistocene and Holocene eruptive centers. The volcano and its wilderness area sit on a lava platform with an altitude of , and they are bounded by faults to the east and west. Volcanic rocks contained within the wilderness area are either composed of older basalt or younger basaltic andesite, all of which were produced during the Quaternary, probably during the past 700,000 years.
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In total, the Belknap shield and its multiple vents were formed in less than 1,500 years, its last eruptive episode finishing about 1,500 years ago. Belknap formed on the lower slopes of Mount Washington, a highly eroded volcano, and is one of the larger mafic (rich in magnesium and iron) volcanoes in the Sisters Reach. Belknap consists of a shield volcano and pyroclastic cone and consists of basaltic and basaltic andesite lava with sub-alkaline composition, and it is characteristic of High Cascade volcanism. Well-preserved, its core is made of cinder materials; its eruptive deposits have well-preserved pressure ridges (tumuli) and levees.
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However, disseminated and low tenor nickel mineralisation is known from the other ultramafic units, especially the Western Ultramafic Unit (WUU). The general stratigraphy of the belt is, from base upwards, a thick sequence of felsic orthogneiss composed of fragmental to glomerocrystic feldspar gneiss, known as the footwall felsic sequence; the ultramafic units of komatiite affinity, 'overlain' by grunerite-magnetite- quartz-amphibole banded iron formation of the Honman Formation, tholeiitic basalt and metasedimentary rocks. Regionally, several subvolcanic lopolithic layered intrusions have been identified from mapping and drilling. These are interpreted to represent the feeder conduits to extrusive ultramafic and mafic igneous rocks stratigraphically higher in the belt.
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313 The Andean Central Volcanic Zone runs along the Western Cordillera of the Andes and along the Altiplano. During the Neogene, the position of this volcanic arc moved eastward and the arc became broader, probably due to a change in the tilt of the slab of the Nazca Plate. Volcanic activity during this time was heavily influenced by local strike-slip faults which acted to channel the magma flows. About 7 million years ago, tectonics and volcanic activity changed in the region probably in response to the delamination of the crust beneath the region: Large scale ignimbrites were erupted at Galán and small back-arc volcanoes erupted mafic basaltic andesite lavas.
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These are overlain by Paleoproterozoic rocks which were formed in rift basins. The Western Block consists of an Archean (2.6–2.5 billion years ago) basement which comprises tonalite-trondhjemite-granodiorite, mafic igneous rock, and metamorphosed sedimentary rocks. The Archean basement is overlain unconformably by Paleoproterozoic khondalite belts, which consist of different types of metamorphic rocks, such as graphite-bearing sillimanite garnet gneiss. Sediments were widely deposited in the Phanerozoic with various properties, for example, carbonate and coal bearing rocks were formed in the late Carboniferous to early Permian (307-270 million years ago), when purple sand-bearing mudstones were formed in a shallow lake environment in the Early to Middle Triassic.
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Barnes’ research spans field geology, petrology, silicate and platinum group mineralogy, analytical chemistry, geochemical and experimental studies, and numerical modelling. Her research interests are in trace element geochemistry, studying ore deposits of nickel, copper, and platinum-group elements and their partition coefficients, and petrogenesis of komatiites, layered intrusions, and granites. She is also interested in nelsonites and deposits of iron, titanium, and vanadium oxides and their respective partition coefficients. Her primary research topics involve the origin of mafic and ultramafic magmas, the ore deposits associated with them, and the processes that occur to form concentrations of certain metals in mineral deposits of economic grade.
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The elements concentrated in these types of rocks are nickel, copper, titanium, vanadium, and platinum-group elements (platinum, palladium, rhodium, iridium, osmium, and ruthenium), which are normally collected from mafic magma by oxide minerals or sulphide liquid. The purpose of her research is to resolve when and why sulphide liquid or oxide minerals separate from magma. She also studies where and why sulphide liquid or oxide minerals collect with metals. One crucial aspect of her research uses a technique developed at the University of Quebec in Chicoutimi to determine platinum-group elements and other trace metals at low concentrations in most types of rocks.
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The most voluminous volcanic rocks of the ocean floor are the mid-oceanic ridge basalts, which are derived from low-potassium tholeiitic magmas. These rocks have low concentrations of large ion lithophile elements (LILE), light rare earth elements (LREE), volatile elements and other highly incompatible elements. There can be found basalts enriched with incompatible elements, but they are rare and associated with mid-ocean ridge hot spots such as surroundings of Galapagos Islands, the Azores and Iceland.Clare P. Marshall, Rhodes W. Fairbridge (1999) Encyclopedia of Geochemistry, Kluwer Academic Publishers Prior to the Neoproterozoic Era 1000 Ma ago as world's oceanic crust was more mafic than present-days'.
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The southern end of the peninsula includes a series of mafic pillow lavas, volcanigenic sediments, shales and limestones, collectively known as the "Burin Group", as well as a 1500 m thick sill of gabbro about 760 million years old. The northern end of the peninsula is defined by the "Marystown Group", primarily carbon-lacking Silica-based sediments which span the Precambrian-Cambrian boundary. The sediments were probably deposited in shoreline environments along the former Iapetus Ocean. The global stratotype at Fortune Head is composed of the uppermost part of member 1 and all of member 2 of the Chapel Island Formation of the Marystown Group.
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Except in acid or siliceous igneous rocks containing greater than 66% of silica, known as felsic rocks, quartz is not abundant in igneous rocks. In basic rocks (containing 20% of silica or less) it is rare for them to contain as much silicon, these are referred to as mafic rocks. If magnesium and iron are above average while silica is low, olivine may be expected; where silica is present in greater quantity over ferro- magnesian minerals, such as augite, hornblende, enstatite or biotite, occur rather than olivine. Unless potash is high and silica relatively low, leucite will not be present, for leucite does not occur with free quartz.
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The relative influence of volcanoes on the Junge layer varies considerably according to the number and size of eruptions in any given time period, and also of quantities of sulfur compounds released. Only stratovolcanoes containing primarily felsic magmas are responsible for these fluxes, as mafic magma erupted in shield volcanoes doesn't result in plumes which reach the stratosphere. Creating stratospheric sulfur aerosols deliberately is a proposed geoengineering technique which offers a possible solution to some of the problems caused by global warming. However, this will not be without side effects and it has been suggested that the cure may be worse than the disease.
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The Tuhua orogeny was a regional orogeny between 370 and 330 million years ago, now preserved in the Fiordland region of New Zealand. Early Paleozoic rocks such as Ordovician greywacke, slate and paragneiss in the Buller terrane, weakly metamorphosed greenschist and sub-greenschist rocks, Cambrian mafic volcanics, Ordovician limestone and Silurian clastic rocks were all deformed and metamorphosed. In addition, between 380 and 250 million years ago, metasediments reached amphibolite grade in the sequence of metamorphic facies. In 1978, G.W. Grindley proposed that the Tuhua orogeny emplaced the Central Belt as a stack of nappe formations, with recumbent folding, thrusting and axial plane schistosity.
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Lava dams are formed by lava flowing or spilling into a river valley in sufficient quantity and height to temporarily overcome the explosive nature (steam) of its contact with water, and the erosive force of flowing water to remove it. The latter depends on the quantity of water flow and stream gradient. The lava may flow during numerous successive or repetitive eruptions and may emanate from single or numerous vents or fissures. Lava of this nature, like basalt, is usually associated with less explosive eruptions; more viscous lavas with lower mafic content, like dacites and rhyolites, can also flow, but tend to be more closely associated with eruptions of greater explosiveness and the formation of pyroclastics.
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Stratovolcanoes developed on top of these ignimbrite sheets and today form the most clear expression of volcanic activity in the region, with some of them exceeding the height of above sea level. The long-lasting dry climate means that traces of volcanic activity can be recognizable over long timeframes. The Altiplano-Puna volcanic complex is underpinned by a large seismic velocity anomaly at a depth of , which may be the largest structure consisting of near- molten (10–20%) rock on Earth. This partial melt zone was formed by the injection of mafic magmas into the lower crust; a major episode of overturning before 10.6 million years ago caused crustal anatexis and started the onset of ignimbritic volcanism.
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Igneous oceanic plateaus have a ratio intermediate between continental and oceanic crust, although they are more mafic than felsic. However, when a plate carrying oceanic crust subducts under a plate carrying an igneous oceanic plateau, the volcanism which erupts on the plateau as the oceanic crust heats up on its descent into the mantle erupts material which is more felsic than the material which makes up the plateau. This represents a step toward creating crust which is increasingly continental in character, being less dense and more buoyant. If an igneous oceanic plateau is subducted underneath another one, or under existing continental crust, the eruptions produced thereby produce material that is yet more felsic, and so on through geologic time.
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Platinum group minerals occur many places throughout the world in layered mafic and ultramafic intrusions formed at high magmatic temperatures, such as the Great Merensky Reef deposits of the Bushveld Igneous Complex in Transvaal Province, South Africa and the Precambrian Stillwater Complex in Montana. Braggite has also been found as euhedral grains in platinum-iron nuggets from alluvial deposits in remote regions of eastern Madagascar. The possible sources for these nuggets can be traced to ultramafic facies composed primarily of pyroxenites, peridotite and serpentine, and tremolite and soapstone. In solution, cooperite forms the first solid at just above the 1100 °C threshold, braggite at around 1000 °C, and lastly vysotskite at temperatures below 900 °C.
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Nyiragongo's lavas are made of melilite nephelinite, an alkali-rich type of volcanic rock whose unusual chemical composition may be a factor in the unusual fluidity of the lavas there. Whereas most lava flows move rather slowly and rarely pose a danger to human life, Nyiragongo's lava flows may race downhill at up to . This is because of the extremely low silica content (the lava is mafic). Hawaiian volcanic eruptions are also characterized by lavas with low silica content, but the Hawaiian volcanoes are broad, shallow-sloped shield volcanoes in contrast to the steep-sided cone of Nyiragongo, and the silica content is high enough to slow most Hawaiian flows to walking pace.
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Zhao et al.'s model can be divided into two major stages: Neoarchean crustal accretion and Paleoproterozoic amalgamation of the two sub-blocks (Yinshan Block and Orods Block). Zhao and other researchers proposed that there was a major crustal accretion of the juvenile Yinshan Block at about 2.7 billion years ago, forming a thick mafic crust, although it is still uncertain whether the magmatic event occurred in a continental or an oceanic setting. During 2.55-2.50 billion years ago, the juvenile Yinshan Block was partially melted to produce enormous amounts of TTG rocks, covering the whole Yinshan Block. At about 2.45 billion years ago, Ordos Block was subducted beneath the Yinshan Block.
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This is because the peralkaline content of these felsic lavas decreased the viscosity of the flows a minimum of 10–30 times over that of calc-alkaline felsic flows. Evidence for explosive volcanism exists in the form of pumice flows, bedded tuffs, intensely shattered basement rocks and the high content of coarse basement clasts in rhyolite breccias. Magma production of the Anahim hotspot has shifted from more felsic to more mafic compositions in the last 3.0 million years. For instance, much of the magma created between 3.0 and 0.33 million years ago was igneous phonolite, trachyte, trachyandesite, basalt and basanite; the volcanoes built during this period are almost entirely made of these rock types.
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A method of 40Ar–39Ar (argon–argon dating) of the SMI volcanic yields is reportedly more reliable of the plateau and isochron ages. The weighted mean isochron age is reported to be 85.6±0.9 Ma (2σ). The K–Ar (potassium-argon dating) technique adopted for the southern Indian Precambrian terrain, intruded by numerous mafic–doleritic dyke swarms, the age from Proterozoic to the latest Cretaceous is reported as 69–66 Ma (Deccan-related). The two regional dykes (a leucograbbro and a felsite) from the Kerala region of southwestern India, which were also dated earlier, indicate the age as 85 Ma. Madagascar flood basalt province's 40Ar–39Ar ages of 89–85 Ma tallies with the SMI volcanic age.
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The horizontal movement of the magma is limited by the viscosity, which leads to the magma pushing the rock above it up creating a dome shape. Lopoliths are believed to have a more mafic, and therefore less viscous, source. Lopoliths tend to be larger than laccoliths, and are believed to get their lenticular shape from the weight of the intruding magma compressing the underlying country rock, or the shape comes from the evacuation of a magma chamber below the intruding magma, causing the country rock to collapse and creating a basin. Some of these terms might be outdated, and not accurately describe the shape of a pluton but they are still commonly used.
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The Circum-Superior Belt is a widespread Paleoproterozoic large igneous province in the Canadian Shield of Northern, Western and Eastern Canada. It extends more than from northeastern Manitoba through northwestern Ontario, southern Nunavut to northern Quebec. Igneous rocks of the Circum-Superior Belt are mafic-ultramafic in composition, deposited in the Labrador Trough near Ungava Bay, the Cape Smith Belt near the southern shore of Hudson Strait and along the eastern shore of Hudson Bay in its northern portion; the Thompson and Fox River belts in the northwest and the Marquette Range Supergroup in its southern portion. The Circum Superior Belt also hosts a rare example of Proterozoic Komatiite, in the Winnipegosis komatiite belt.
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At 1,900 and 1,800 million years ago, an ocean closure and collision with the Wisconian arc terrane resulted in the creation of the Penokean orogeny at the southern Superior craton margin. The last collision occurred on the southeastern portion of the Superior craton to produce the Grenville orogeny 1,100 million years ago. Because most of the Circum-Superior Belt was formed by widespread mafic-ultramafic magmatism 1,884 to 1,870 million years ago along the Superior craton margin during these orogenies, a number of different suggestions have been made to explain the questionable origins of this large igneous province. It is also not clear if the Circum-Superior Belt has a single origin or it has several origins.
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These basaltic lavas are intruded by narrow mafic and ultramafic sills. At least three different types of lava compositions exist in the Chukotat Group, including olivine phyric, pyroxene-phyric and plagioclase phyric. The upper unit of the Chukotat Group is 1,870 million years old whereas the lower unit is associated with the Katiniq Suite sills, which cut through the underlying Povungnituk Group. In 1989, the Katiniq Suite sills were thought to be 1,918 million years old, but more recent dating and a reinterpretation of the original age in 2004 suggests that the Katiniq Suite sills are closer to 1,880 million years old. Therefore, the age range for the Chutotat Group is 1,880 to 1,870 million years.
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There is a connection between volcanism and crustal thickness on the subsurface of Io. Thinner crust produces dense, mafic, dark flows that cover larger areas and where secondary, more sulfurous flows occur. Conversely, in thicker crust regions, the more dense lavas do not occur as often. Crustal thickness is thought to be related to tidal flexing in the interior of Io. The shift from dark, freshly erupted material into bright plains material may support the notion that Io has strong crustal materials that can support the steep paterae walls. The lithosphere of Io is thought to be well-fractured, which is supported by the paterae hot spot migration between the times of the Voyager and the Galileo flybys.
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The island of Tobago is situated on the Tobago terrane, a section of crust bounded by the South American and Caribbean plates. It is bounded by faults formed from the Cretaceous to the present and comprises Cretaceous oceanic crust, volcanogenic and pelagic marine sedimentary rocks, late Cretaceous and Paleogene island arc volcanic rocks and overlying sedimentary rocks from the Neogene. The original mafic oceanic crust formed more than 120 million years ago and was then underplated and deformed by the continental Araya-Margarita Terrane 90 million years ago, which drove volcanic activity and formed a forearc basin. In the Paleogene, the region was denuded by erosion and then overridden by the Paria- Trinidad Terrane.
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Igneous activity ended around 1.3 billion years ago, with the intrusion of numerous dikes and sills into newly crystallized rhyolite and granite. Although not directly impacting the current boundaries of Missouri, the Midcontinent Rift System formed from 1.2 to one billion years ago as mafic lave erupted in a rift zone spanning Lake Superior through Iowa to Kansas. Laurentia was included in the supercontinent Rodinia from one billion to 541 million years ago and no new rock formation took place in Missouri. Failed rifting of the continent produced the Reelfoot Rift, which extends beneath the Mississippi Embayment to the southeast lowlands of the state and intersects the Missouri Gravity Low, creating the New Madrid Seismic Zone.
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The andesite line is the most significant regional distinction in the Pacific. A petrologic boundary, it separates the deeper, mafic igneous rock of the Central Pacific Basin from the partially submerged continental areas of felsic igneous rock on its margins. The andesite line follows the western edge of the islands off California and passes south of the Aleutian arc, along the eastern edge of the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands, the Solomon Islands, and New Zealand's North Island. Ulawun stratovolcano situated on the island of New Britain, Papua New Guinea The dissimilarity continues northeastward along the western edge of the Andes Cordillera along South America to Mexico, returning then to the islands off California.
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The unit was initially interpreted by the Geological Survey to be a conglomerate with clasts derived from mafic dykes. Later interpretations invoked a volcanic origin for the unit, based on the presence of pieces of green devitrified glass, with pyroclastic flow, peperite, tuff and lahar all being proposed. When shocked quartz, a higher than expected concentration of platinum group metals and the presence of a non-terrestrial chromium isotope were all identified in the unit, it was reinterpreted as part of an impact ejecta blanket. Evidence for a meteorite impact close to Ullapool was published by a combined team of scientists from the University of Oxford and the University of Aberdeen, in March 2008.
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Composed of of basaltic andesite and of andesite, Diamond Peak is a shield volcano, though it might be considered a "modest stratocone" because of its steep slopes and the pyroclastic materials at its core. Having produced andesite, Diamond Peak represents one of the few mafic shield volcanoes in the Cascades that are known to grade into andesite, along with Mount Defiance, Mount Bailey, Devils Peak, and Prospect Peak. It consists of a main cone made of pyroclastic material including palagonitized rock along with basaltic andesite cinders and glassy scoria, as well as thin layers of basaltic andesite lava flows. Diamond Peak has two overlapping volcanic cones, with the elder edifice making up its lower northern peak.
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The energy required to melt the outer portion of the Moon is commonly attributed to a giant impact event that is postulated to have formed the Earth-Moon system, and the subsequent reaccretion of material in Earth orbit. Crystallization of this magma ocean would have given rise to a mafic mantle and a plagioclase-rich crust. Geochemical mapping from orbit implies that the crust of the Moon is largely anorthositic in composition, consistent with the magma ocean hypothesis. In terms of elements, the lunar crust is composed primarily of oxygen, silicon, magnesium, iron, calcium, and aluminium, but important minor and trace elements such as titanium, uranium, thorium, potassium, and hydrogen are present as well.
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The Isua Greenstone Belt, also known as the Isua supracrustal belt since it is composed of supracrustal rock deposited upon basement rock strata, is located in the southwestern portion of Greenland, in the Isukasia terrane, near the Nuuk capital region. The greenstone belt is made up of metamorphosed mafic volcanic and sedimentary rocks that are usually juxtaposed by mylonites or fault boundaries. By using uranium-lead dating on zircon and titanite, the tectonic history was dated to be approximately 3,700–3,600 million years old. The Isua Greenstone has been studied by Earth scientists due to evidence the area holds for early Earth plate tectonics, since it houses one of the oldest, best-preserved ancient plate tectonic sequences.
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A reconstruction of the origin of continental crust, which formed the greenstone belt, using geochemical, lithological, and structural clues, is predicated upon two assumptions: first, new Hadean crust formed laterally by the expelling and lateral accretion of mafic to ultramafic lavas. Then stabilization occurred through the re-melting of the crust. The reworked crust can be attributed to the burial, most likely through subduction, of hydrated materials, such as basalt, that were formed in the Hadean. Additionally, the source for tested rock samples came from a mantle depleted in titanium and niobium and enriched in lead, strontium, barium, rubidium, and light rare- earth elements, which, taken together, are indicative of arc-related basalts.
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Dredging has produced basaltic and carbonatic rocks that are partly covered by ferromanganese crusts or chemically altered by phosphate. In addition, shallow water calcarenites, conglomerates, coral debris, hemipelagic sediments, breccia, limestones, felsite, foraminiferal sand, pelagic ooze, reefal limestones and sediments have been recovered. The volcanic rocks include alkali basalts, basanite, hyaloclastite, palagonite, picrite, pumices, basaltic tuffs, trachybasalt and trachyte and define an alkaline ocean island basalt suite although the existence of tholeiites as in Hawaii is possible and substantial amounts of evolved volcanic rocks have been recovered; these were probably generated by basaltic melts in magma chambers. Minerals contained in the rocks include mafic clots, amphibole, apatite, clinopyroxene including augite, olivine, plagioclase, spinel and titanomagnetite.
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The bedrock underlying Florenceville- Bristol at its oldest is part of the White Head Formation consisting of limestone and calcareous shales of Late Ordovician to Early Silurian in age. Later in history more sedimentary rocks were deposited forming the Smyrna Mills Formation during the Silurian, consisting of shales, limestones, and conglomerates. The range of mountains from North to South along the Eastern side of the Saint John River known as Carr Mountain, The Pinnacle, and Oakland Mountain (N to S) are also part of the Smyrna Mills Formation and consist of mafic volcanic flows (basalt) and tuff. Within these mountains there are also two gabbro tubes that are Early Devonian in age.
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Jefferson is the largest volcano in the Jefferson Reach, which forms the strip that makes up the northern part of the Oregon Cascade Range. Stretching from Frog Lake Buttes to South Cinder Peak, this segment consists of at least 175 Quaternary volcanoes. With a width of , it differs from the adjacent northern segment of the Cascades, where volcanoes show a scattered distribution. Other unusual features of the Jefferson Reach include that the northernmost of the strip does not contain many volcanoes formed since the early Pleistocene and that it features a number of andesitic and dacitic volcanoes, which are unlike the many mafic (rich in magnesium and iron) shield volcanoes within the stretch.
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Rhyodacitic lava flows and pyroclastic material, which have since been significantly altered and stripped by glaciation, originated from eight vents in the area. The Mount Jefferson vicinity contains at least 40 of the 190 documented lava domes in the Oregon Cascades, including the tall Goat's Peak dome; it also contains monogenetic tuyas (flat-topped, steep-sided volcanoes formed when lava erupts through a thick glacier or ice sheet) and emplacements of hyaloclastite among mafic lava flows. The area is full of cinder cone volcanoes and intrusive lava plugs, which occur in irregular patterns. Made up of red to gray cinders, some are loose and agglutinated, and some contain intrusive rock plugs, while others do not.
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The ice has been used to reconstruct past climate states in West Antarctica, including the beginning and end of the last interglacial, and shows evidence that the West Antarctic Ice Sheet collapsed during that interglacial. In addition, recognizable tephra layers are found in this ice and appear to originate from explosive eruptions of volcanoes such as Mount Berlin, Mount Takahe and Mount Waesche. These tephra layers at Mount Moulton crop out in parallel layers and geochemical traits indicate an origin at Mount Berlin although some layers may have been erupted from mafic volcanoes at Mount Moulton and Mount Berlin. Furthermore, the appearance of the deposits indicates that the eruptions of Mount Berlin were highly explosive.
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Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick; however, it is denser, having a mean density of about 3.0 grams per cubic centimeter as opposed to continental crust which has a density of about 2.7 grams per cubic centimeter. The crust uppermost is the result of the cooling of magma derived from mantle material below the plate. The magma is injected into the spreading center, which consists mainly of a partly solidified crystal mush derived from earlier injections, forming magma lenses that are the source of the sheeted dikes that feed the overlying pillow lavas.
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Map of the Mackenzie dike swarm The Mackenzie dike swarm, also called the Mackenzie dikes, form a large igneous province in the western Canadian Shield of Canada. It is part of the larger Mackenzie Large Igneous Province and is one of more than three dozen dike swarms in various parts of the Canadian Shield. The Mackenzie dike swarm is the largest dike swarm known on Earth,Suppressing Varying Directional Trends Retrieved on 2007-07-28 more than wide and long, extending in a northwesterly direction across the whole of Canada from the Arctic to the Great Lakes. The mafic dikes cut Archean and Proterozoic rocks, including those in the Athabasca Basin in Saskatchewan, Thelon Basin in Nunavut and the Baker Lake Basin in the Northwest Territories.
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The Little Cottonwood stock is a granitic intrusion that extends from the mouth of the canyon almost to Snowbird ski resort. It is Oligocene in age, roughly 30.5 to 29 million years old, composed primarily of granodiorite, quartz monzonite, and granite, with some mafic enclaves. The Little Cottonwood stock is intruded in its northeast corner by another unit called the White Pine intrusion, and other smaller igneous units, collectively about 27-26 million years old, which are the source of the inactive White Pine molybdenum ore deposit in White Pine fork. The intrusion and its associated ore deposit have several interesting features, including quartz-bearing porphyry, pebble dikes, and other features related to hydrothermal ore deposit processes, and possibly volcanism, that occurred during intrusion.
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Indian Heaven consists of several, overlapping shield volcanoes that run along a line from Sawtooth Mountain at the north to Red Mountain to the south, as well as cinder cones, lava flows, and spatter cones (low, steep- sided hills or mounds that consist of welded lava fragments). With a total magma output of , the field has about 50 mafic eruptive edifices (rich in magnesium and iron), whose activity lasted from the Pleistocene to the early Holocene. Roughly half of these vents mark a mountainous highland, in length, which runs parallel to the north–south trend of the Cascade Arc in southern Washington state. Most of the volcanoes that comprise the Indian Heaven field are monogenetic, only erupting once before becoming extinct.
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Geologically, southwestern Utah is at the margin between the geologic provinces known as the Colorado Plateau and the Basin and Range Province, the former of which features flat lying sediments while the latter is characterized by steep horsts and grabens. After the Oligocene and Miocene, during which volcanism was characterized by calderas and stratovolcanoes, beginning 8 million years ago smaller volumes of mostly mafic magma formed lava domes, shield volcanoes, volcanic cones and volcanic plugs. The Markagunt Plateau is part of the High Plateaus geologic province, in the Colorado Plateau and at its margins with the Basin and Range Province. It is a wide fault-bounded block and the basement underneath the volcanoes is formed by various Cretaceous to Miocene sedimentary or volcanic rocks.
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Erratic eruptions continued afterward, erupting silicic lava off and on until 150,000 years ago, including pyroxene andesites that lacked olivine, as well as obsidian, which was rare among local volcanoes during that time period. Much of the current cone is occupied by flows from eruptions of mafic lava (rich in magnesium and iron) including andesite, dacite, rhyodacite, and pyroclastic flows. These deposits extend from the subordinate volcano to the summit, and reach Todd Lake Volcano as well as rhyodacitic lava at Tam MacArthur rim and Whychus Creek Falls. Another set of rhyodacitic lava domes runs for from south of Broken Top to Demaris Lake to its north, but they were partially covered by andesitic deposits from eruptions at the South Sister volcano.
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This is an AFM diagram, a ternary diagram showing the relative proportions of the oxides of Na2O + K2O (A), FeO + Fe2O3 (F), and MgO (M). The arrows show the path of the magmas in the tholeiitic and the calc- alkaline magma series. Rocks from the calc-alkaline magma series are distinguished from rocks from the tholeiitic magma series by the redox state of the magma they crystallized from (tholeiitic magmas are reduced, and calc- alkaline magmas are oxidized). When mafic (basalt-producing) magmas crystallize, they preferentially crystallize the more magnesium-rich and iron- poor forms of the silicate minerals olivine and pyroxene, causing the iron content of tholeiitic magmas to increase as the melt is depleted of iron-poor crystals.
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They are called "sanukitoid" because of their similarity in bulk chemical composition to high-magnesium andesite from the Setouchi Peninsula of Japan, known as "sanukites" or "setouchites" (Tatsumi and Ishizaki 1982). Sanukite rocks are an andesite characterized by orthopyroxene as the mafic mineral, andesine as the plagioclase, and a glassy groundmass. Rocks formed by processes similar to those of sanukite may have compositions outside the sanukitoid field. The term was originally defined by Stern et al. (1989) to refer to plutonic rocks containing between 55 and 60 weight percent SiO2, with Mg# >0.6, Ni >100 ppm, Cr >200 ppm, K2O >1 weight percent, Rb/Sr <0.1, Ba >500 ppm, Sr >500 ppm, enrichment in LREEs, and no or minor Eu anomalies.
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Sperrylite is the most common platinum mineral, it generally occurs with a wide array of other unusual minerals, including cooperite [(Pt,Pd,Ni)S], laurite [RuS2], kotulskite [Pd(Te,Bi)], merenskyite [(Pd,Pt)(Te,Bi)2], iridium-osmium (Ir-Os) alloys, sudburyite [(Pd,Ni)Sb], omeiite [(Os,Ru)As2], testibiopalladite [PdTe(Sb,Te)], and niggliite [PtSn], to name a few. It does not readily decompose through normal weathering processes and, consequently, has been reported in widely scattered alluvial deposits. It was first found as tiny crystals found with rhodolite garnet and corundum during alluvial gem mining in streams draining Mason Mountain, Macon County, North Carolina (Hidden 1898). Sperrylite has been identified in Finland from sulfide deposits generally associated with layered mafic-ultramafic complexes.
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The break-up of Pangaea resulted in the opening of the Atlantic Ocean in three stages The Atlantic Ocean is underlain mostly by dense mafic oceanic crust made up of basalt and gabbro and overlain by fine clay, silt and siliceous ooze on the abyssal plain. The continental margins and continental shelf mark lower density, but greater thickness felsic continental rock that often much older than that of the seafloor. The oldest oceanic crust in the Atlantic is up to 145 million years and situated off the west coast of Africa and east coast of North America, or on either side of the South Atlantic. In many places, the continental shelf and continental slope are covered in thick sedimentary layers.
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Galileo observed the effects of a major eruption at Pillan Patera and confirmed that volcanic eruptions are composed of silicate magmas with magnesium-rich mafic and ultramafic compositions. Distant imaging of Io was acquired for almost every orbit during the primary mission, revealing large numbers of active volcanoes (both thermal emission from cooling magma on the surface and volcanic plumes), numerous mountains with widely varying morphologies, and several surface changes that had taken place both between the Voyager and Galileo eras and between Galileo orbits. The Galileo mission was twice extended, in 1997 and 2000. During these extended missions, the probe flew by Io three times in late 1999 and early 2000 and three times in late 2001 and early 2002.
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The low pressure group has formed along geotherms around 20-30 °C/km, which are comparable to those during the underplating of plateau bases. Mantle upwellings add mafic basement to the crust and the pressure due to the cumulation thickness may reach the requirement of low pressure TTG production. The partial melting of the plateau base (which can be induced by further mantle upwelling) would then lead to low pressure TTG generation. The high pressure TTGs have experienced geotherms lower than 10 °C/km, which are close to modern hot subduction geotherms experienced by young slabs (but around 3 °C/km hotter than other modern subduction zones), whilst the geotherms for the most abundant TTG subseries, medium pressure group, are between 12 and 20 °C/km.
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The two submarine volcanoes are capped by hawaiite and are surrounded by numerous smaller vents, with a total edifice volume of about 12 km3. The lava emitted in eruptions at the Tuzo Wilson Seamounts is made of basalt, a common gray to black or dark brown extrusive volcanic rock low in silica content (the lava is mafic) that is usually fine-grained due to rapid cooling of lava. Glassy pillow lava is found at the seamounts, a type of rock typically formed when basaltic lava emerges from a submarine volcanic vent. The viscous lava gains a solid crust on contact with the water, and this crust cracks and oozes additional large blobs or "pillows" as more lava emerges from the advancing flow.
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This volcanic activity built an extensive lava plateau and large igneous province with an area of representing a volume of lavas of at least . With an area of and a volume of at least , it is larger than the Columbia River Basalt Group in the United States and comparable in size to the Deccan Traps in west-central India, making it one of the largest flood basalt events ever to appear on the North American continent, as well as on Earth. This massive eruptive event was associated with the Mackenzie magmatic event, that included the coeval, layered, mafic- ultramafic Muskox intrusion and the enormous Mackenzie dike swarm that diverges from the Coppermine River flood basalts. The maximum thickness of the flood basalts are and consist of 150 lava flows, each thick.
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Basalt (, )American Heritage DictionaryMerriam-Webster DictionaryCollins English DictionaryOxford Living Dictionaries is a mafic extrusive igneous rock formed from the rapid cooling of lava rich in magnesium and iron exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt, and the eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flows that can spread over great areas before cooling and solidifying. Flood basalts are thick sequences of many such flows that can cover hundreds of thousands of square kilometers and constitute the most voluminous of all volcanic formations.
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The materials forming the valley floor of the system are thought to be ultramafic or mafic in composition, characterized by an abundance of Fe and a relative dearth of K and Th based on data from the Gamma Ray Spectrometer (GRS). Some aeolian exhumation is observed to have resurfaced the floor. Furthermore, large-scale extension and compression are evident in the Athabasca Valles floor unit, which may have been associated with earlier regional tectonic events or the emptying of an underlying magma chamber. The volcanic unit proposed to compose the floor of the Athabasca Valles (among other terrains) is hypothesized by some researchers to be the youngest and largest flood-emplaced lava unit on Mars, and the only instance of a flood lava unit that displays morphological evidence of turbulent flow.
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Serpentinization is a geological low-temperature metamorphic process involving heat and water in which low- silica mafic and ultramafic rocks are oxidized (anaerobic oxidation of Fe2+ by the protons of water leading to the formation of H2) and hydrolyzed with water into serpentinite. Peridotite, including dunite, at and near the seafloor and in mountain belts is converted to serpentine, brucite, magnetite, and other minerals – some rare, such as awaruite (Ni3Fe), and even native iron. In the process large amounts of water are absorbed into the rock increasing the volume, reducing the density and destroying the structure.Serpentinization: The heat engine at Lost City and sponge of the oceanic crust The density changes from 3.3 to 2.7 g/cm3 with a concurrent volume increase on the order of 30-40%.
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Chemical analysis, of the volcanic rocks, suggests that this phase of volcanic activity was started by the injection of mafic magma into the magma chamber. This eruption displaced between 4,000 and 1,500 people in the region. After the large 1990 eruption, the style of activity at Sabancaya changed towards a frequent occurrence of explosive eruptions with however low output, which threw ballistic blocks to distances of about from the summit crater; this pattern of activity is referred to as "Vulcanian eruptions". These explosive eruptions became less common over time (from paroxysms every 20–30 minutes to only 5–6 eruptions per day) and the proportional amount of fresh volcanic material increased at first; since 1997 discontinuous eruptions generate steam columns no higher than and ejected material is almost entirely lithic.
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Epigenetic change (secondary processes occurring at low temperatures and low pressures) may be arranged under a number of headings, each of which is typical of a group of rocks or rock-forming minerals, though usually more than one of these alterations is in progress in the same rock. Silicification, the replacement of the minerals by crystalline or crypto- crystalline silica, is most common in felsic rocks, such as rhyolite, but is also found in serpentine, etc. Kaolinization is the decomposition of the feldspars, which are the most common minerals in igneous rocks, into kaolin (along with quartz and other clay minerals); it is best shown by granites and syenites. Serpentinization is the alteration of olivine to serpentine (with magnetite); it is typical of peridotites, but occurs in most of the mafic rocks.
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The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it fractionally crystallizes to become a felsic magma, which is low in magnesium and iron and produces rhyolite or granite. Calc- alkaline rocks are rich in alkaline earths (magnesia and calcium oxide) and alkali metals and make up a major part of the crust of the continents. The diverse rock types in the calc-alkaline series include volcanic types such as basalt, andesite, dacite, rhyolite, and also their coarser-grained intrusive equivalents (gabbro, diorite, granodiorite, and granite).
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The Mawson craton of East Antarctica and Australia preserves evidence of tectonic activity from the Archean through the Mesoproterozoic in the Terre Adelie, King George V Land and the Miller Range of the central Transantarctic Mountains.Fitzsimmons, 2003 The Late Proterozoic Rayner Complex outcrops in Enderby Land and western Kemp Land. The Rauer Islands terrane, composed of the Rauer Group granulite gneisses, are Late Proterozoic (1106 Ma). Numerous mafic dykes are present in the Vestfold Hills and Napier Complex, and were emplaced between about 1200 to 1400 Ma. Massive charnockite bodies are present in the East Antarctica complex Proterozoic mobile belts, indicating a batholith intruded the supracrustal basement gneiss around 1000 Ma. In the Borg Massif region of western Dronning Maud Land, Archaean granites are overlain by the Proterozoic Ritscherflya Supergroup.
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This volcanic activity built an extensive lava plateau and large igneous province with an area of representing a volume of lavas of at least . With an area of and a volume of , it is larger than the Columbia River Basalt Group in the United States and comparable in size to the Deccan Traps in west-central India, making it one of the largest flood basalt events ever to appear on the North American continent, as well as on Earth. This massive eruptive event was associated with the Mackenzie magmatic event, that included the coeval, layered, mafic-ultramafic Muskox intrusion and the enormous Mackenzie dike swarm that diverges from the Coppermine River Group flood basalts. The maximum thickness of the flood basalts are and consist of 150 lava flows, each to thick.
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Various domes and arcuate ridges have been observed across the cap rock of Ganges Mensa, leading some to speculate that these likely volcanic landforms are actually evidences of magmatic dikes, volcanic vents, or the erosional remnants of volcanic necks that may have intruded underlying layers to deposit the cap rock. The presence of extensive thin layering in the thick friable stratigraphic units underneath Ganges Mensa's cap rock could correspond closely to hyaloclastites, which are volcanic breccias that are formed when lavas are erupted directly into water or ice and then quenched. The proposed hyaloclastite facies have been analogized to those comprising tuyas in Iceland. Other authors have proposed that these layered terrains could constitute alternating mafic flows and tuffs made of palagonite, as has been observed in some Icelandic tuyas.
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World production trend of zirconium mineral concentrates Zircon is a common accessory to trace mineral constituent of most granite and felsic igneous rocks. Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands. Zircon is rare within mafic rocks and very rare within ultramafic rocks aside from a group of ultrapotassic intrusive rocks such as kimberlites, carbonatites, and lamprophyre, where zircon can occasionally be found as a trace mineral owing to the unusual magma genesis of these rocks. Zircon forms economic concentrations within heavy mineral sands ore deposits, within certain pegmatites, and within some rare alkaline volcanic rocks, for example the Toongi Trachyte, Dubbo, New South Wales Australia in association with the zirconium-hafnium minerals eudialyte and armstrongite.
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The typical location for VMS deposits is at the top of the felsic volcanic sequence, within a sequence of volcaniclastic tuffaceous epiclastics, cherts, sediments or perhaps fine tuffs which are usually related to the underlying volcanics. The hangingwall to the deposit is broadly related to a more mafic sequence of volcanic rocks, either andesite (examples being Whim Creek & Mons Cupri, Western Australia or Millenbach, Canada), or basalt (Hellyer, Tasmania) or absent or sediments only (Kangaroo Caves, Western Australia). VMS deposits are associated spatially and temporally with felsic volcanic rocks, usually present in the stratigraphy below the deposit, and often as the direct footwall to the deposit. Sediments are usually contiguous with VMS deposits in some form or another and typically are present as (manganiferous) cherts and chemical sediments deposited within a submarine environment.
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Off the western coast of South America, the Nazca Plate subducts beneath the South America Plate. This subduction is responsible for the volcanism in the volcanic arc, but the presence of the Carnegie Ridge on the subducting plate may modify the extent of volcanism: Whereas the volcanic arc in Colombia is relatively narrow, in Ecuador it is over wide. Pilavo lies west of the main volcanic arc and is constructed on a crust that is in part derived from the Caribbean large igneous province, part of which were integrated on the Ecuadorean coast and gave the crust thus a mafic signature. Otherwise, the basement includes Cretaceous marine and volcanic sequences, and is cut by a number of faults which controlled the location of the volcanic vents including these of Pilavo.
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After dehydration, solute-rich fluids are released from the slab and metasomatise the overlying mantle wedge of MORB-like asthenosphere, enriching it with volatiles and large ion lithophile elements (LILE). The current belief is that the generation of andesitic magmas is multistage, and involves crustal melting and assimilation of primary basaltic magmas, magma storage at the base of the crust (underplating by dense, mafic magma as it ascends), and magma homogenization. The underplated magma will add a lot of heat to the base of the crust, thereby inducing crustal melting and assimilation of lower-crustal rocks, creating an area with intense interaction of the mantle magma and crustal magma. This progressively evolving magma will become enriched in volatiles, sulfur, and incompatible elements – an ideal combination for the generation of a magma capable of generating an ore deposit.
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The East Bull Lake intrusive suite, in the southern Superior province near Sudbury, Ontario, aligns spatially with the Blue Draw Metagabbro if the Superior and Wyoming cratons are restored to the Kenorland configuration proposed by Roscoe and Card (1993). These layered mafic intrusions are of similar thickness and identical age, and occur along a rifted belt. Recent paleomagnetic and geochronological data from the central Wyoming craton support the hypothesis that the Huronian (in southern Ontario) and Snowy Pass (in southeastern Wyoming) supergroups were adjacent to each other at and may have evolved as a single sedimentary rift basin between 2,450 and 2,100 million years ago. These Huronian and Snowy Pass sedimentary rocks are similar, each having 2,450- to 2,100-million-year-old epicratonic rifts succeeded by a 2,100- to 1,800-million-year-old passive sedimentary margins.
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A north-northwest-trending crustal segment transects from Kaminak Lake (central Hearne Domain) in the south to Yathkyed Lake (northern Hearne Domain) in the northwest, consisting of Archean supracrustal belts that preserve mostly Archean mafic to felsic volcanic rocks (greenschist-grade supracrustal and granitoids), metamorphic cooling of hornblende and Proterozoic biotite. This section of the Churchill province was formerly called the Ennadai-Rankin greenstone belt and include the Kaminak, Yathkyed, MacQuoid and Rankin supracrustal belts, containing a wide range of intrusive Neoarchean plutonic rocks ranging in composition from gabbro to syenogranite. The Kaminak supracrustal belt preserves igneous textures including interlocking quartz and plagioclase that are intergrown with platy biotite (2.084-1.914 Ga) and stubby euhedral grains of prismatic titanite and hornblende. The Yathkyed belt contains a range of hornblende cooling (2.63-246 Ga) amphibolitic metamorphic rocks.
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Volcanism is widespread in the western United States and occurs in various forms at various places. Among the better known are the Cascade volcanoes created by subduction off the western coast of North America, which include the caldera of Mount Mazama (created by a large eruption in the early Holocene) as well as stratovolcanoes such as Mount St. Helens and mafic volcanic fields. Other volcanic centres in the United States are those associated with Yellowstone Caldera and Snake River Plain, those along the margins of the Colorado Plateau, volcanoes linked to the Rio Grande Rift and Jemez lineament, and finally volcanoes in the western Basin and Range Province such as the Cima volcanic field. Generally, volcanic activity was widespread in the dry regions of the western United States during the Tertiary and Quaternary, forming several volcanic fields.
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In 2008 an age of 4.28 billion years was reported for an outcrop in the Nuvvuagittuq Greenstone Belt on the eastern shores of Hudson Bay, 40 kilometres south of Inukjuak, Quebec, Canada. However, the dating method used did not involve similar radiometric dating of zircon crystals and it remains somewhat contentious whether the reported date represents the age that the rock itself formed or a residual isotopic signature of older material that melted to form the rock.Discovery of world’s oldest rocks challenged, New Scientist, 26 September 2008 Mafic rocks from the Nuvvuagittuq Greenstone Belt have recorded isotopic compositions that can be produced only in the Hadean eon (i.e. older than 4 billion years ago) and the complete isotopic study of all the lithologies included in the Nuvvuagittuq Greenstone Belt suggests that it was formed nearly 4.4 billion years ago.
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Their formation may be stimulated by the entry of mafic magmas into the magmatic system; such an entry of new magma in a volcanic system is often the trigger for explosive eruptions. The magmas erupted early during the 1600 event (in the first stage of the eruption) appear to have originated from depths of more than ; petrological analysis indicates that some magmas came from depths greater than and others from shallower depths of about . While an older hypothesis by de Silva and Francis held that the entry of water into the magmatic system may have triggered the eruption, a more recent viewpoint argues that the entry of new dacitic magma into a pre-existent dacitic magma system triggered the 1600 eruption; furthermore movement of deep andesitic magmas that had generated the new dacite produced movements within the volcano.
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The origin of modern seafloor smokers and ancient volcanogenic massive sulfide deposits: mafic magma at depth (perhaps a few kilometers beneath the surface) acts as a heat source, causing convective circulation of seawater through the oceanic crust. Volcanogenic massive sulfide (VMS) are responsible for almost a quarter of the world's zinc production while contributing for lead, silver and copper as well. VMS deposits tend to be of great size since they form over a long period of time and have a relatively high grade in valuable minerals. The main minerals in this deposit are sulphide minerals such as pyrite, sphalerite, chalcopyrite and galena. The term “massive sulfide” deposit refers to any deposit containing more than 50% sulfide minerals. The modifier “volcanogenic” indicates that the massive sulfides are believed to be genetically related to volcanism that was ongoing at the time of sulfide deposition.
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Researchers from the United States Geologic Survey (including Windy Jaeger, Lazlo Keszthelyi, and James A. Skinner) and Alfred McEwen (University of Arizona) published a study in 2010 using high- resolution HiRISE and CTX data to map flood lavas in the Athabasca Valles region. The extent of this flood lava unit was found to be approximately the size of the American state of Oregon in extent. CRISM spectral data was used to confirm the composition of the geomorphic units mapped in the course of this effort, and reaffirmed earlier large-scale assertions using GRS spectral data that the Athabasca Valles floor is largely ultramafic and mafic in composition. This work refocused the initial 2007 finding by the researchers that a veneer of lava covered the entirety of the Athabasca Valley floor, proposing that this lava layer was deposited turbulently in a single eruption over a span of weeks.
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The Narryer Gneiss Terrane is a geological complex in Western Australia that is composed of a tectonically interleaved and polydeformed mixture of granite, mafic intrusions and metasedimentary rocks in excess of 3.3 billion years old, with the majority of the Narryer Gneiss Terrane in excess of 3.6 billion years old. The rocks have experienced multiple metamorphic events at amphibolite or granulite conditions, resulting in often complete destruction of original igneous or sedimentary (protolith) textures. Importantly, it contains the oldest known samples of the Earth's crust: samples of zircon from the Jack Hills portion of the Narryer Gneiss have been radiometrically dated at 4.4 billion years old, although the majority of zircon crystals are about 3.6-3.8 billion years old. The Narryer Gneiss Terrane is adjacent to the northernmost margin of the Yilgarn Craton and is abutted on the north by the Gascoyne Complex metasedimentary and metagranite orogen.
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This is higher than the boiling point of sulfur (), indicating a silicate composition for at least some of Io's lava flows. Similar temperatures were also observed at the Surt eruption in 1979 between the two Voyager encounters, and at the eruption observed by Witteborn and colleagues in 1978. In addition, modeling of silicate lava flows on Io suggested that they cooled rapidly, causing their thermal emission to be dominated by lower temperature components, such as solidified flows, as opposed to the small areas covered by still molten lava near the actual eruption temperature. Thermal emission map of Io by Galileo Silicate volcanism, involving basaltic lava with mafic to ultramafic (magnesium-rich) compositions, was confirmed by the Galileo spacecraft in the 1990s and 2000s from temperature measurements of Io's numerous hot spots, locations where thermal emission is detected, and from spectral measurements of Io's dark material.
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Further evidence that indicate lithospheric thickening beneath the middle portion of Stikinia include the increased profusion of cognate inclusion and plagioclase megacrysts in volcanic rocks from the southern portion of the volcanic province, which might be evidence of magma ponding and magma crystallization in the lithosphere before a volcanic eruption, and the restricted existence of petrologically evolved rock types in the southern half of the Northern Cordilleran Volcanic Province. If the developed magmas originated from fractionation of mafic magmas, fractionation associated with lithospheric contamination, or entirely from melting of the associated lithosphere, their existence suggests more dense lithosphere lies under the southern portion of the Northern Cordilleran Volcanic Province. In the Llangorse section of the Atlin Volcanic Field in northwestern British Columbia, a suite of xenoliths confines the thickness of the Northern Cordilleran Volcanic Province mantle lithosphere to as thin as and a thickness no more than . [Abstract of a Poster].
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West of the Norseman–Wiluna Belt is the Yalgoo-Singleton greenstone belt, where complex dolerite dike swarms obscure the volcaniclastic sediments. Large dolerite sills such as the Golden Mile Dolerite can exhibit coarse-grained texture, and show a large diversity in petrography and geochemistry across the width of the sill. The vast areas of mafic volcanism/plutonism associated with the Jurassic breakup of the Gondwana supercontinent in the Southern Hemisphere include many large diabase/dolerite sills and dike swarms. These include the Karoo dolerites of South Africa, the Ferrar Dolerites of Antarctica, and the largest of these, indeed the most extensive of all dolerite formations worldwide, are found in Tasmania. Here, the volume of magma which intruded into a thin veneer of Permian and Triassic rocks from multiple feeder sites, over a period of perhaps a million years, may have exceeded 40,000 cubic kilometres.
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Grosse et al. 2018, p.15 Surrounding volcanoes include Condorito (which is considered to be part of the old El Cóndor volcano), Falso Azufre and Laguna Escondida which have constrained the extent of El Cóndor's lava flows. The volcano rises within the Laguna Amarga caldera,Grosse et al. 2018, p.14 and an older mafic monogenetic volcano lies north of El Cóndor.Grosse et al. 2018, p.15 Radiometric dating has yielded ages of 2.89 - 2.67 million years ago to 0.13 - 0.02 million years ago, with the volcano developing in two phases.Grosse et al. 2018, p.14 The older group of ages has been obtained on the Condorito and the older edifice, while the ages of 130,000 years ago and younger come from the younger edifice and lava flows; some of these dates have high uncertainties (one young age is 20,000 ± 30,000 years ago from the western flank)Grosse et al.
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The land that is today Nebraska originated as a juvenile crust expansion of the continent Laurentia—today part of the North American Craton and the core of the North American continent—between 1.8 and 1.6 Ga (billion years ago). Tectonic models suggest that Laurentia was part of the supercontinent Columbia but returned to being an independent continent between 1.35 and 1.3 Ga after which it became joined first to Protorodinia and the supercontinent Rodinia by 1.07 Ga. The Precambrian basement rocks of Nebraska are known from the large number of wells bored in the state, which reveal large terranes of gneissic granitic rock, muscovite schist, biotite schist, quartzite and metasedimentary rocks. Although drilling has revealed small instances of amphibolite and metavolcanic rock, gabbro and anorthosite, no mafic or plutonic rocks have been found in Nebraska or neighboring states. Research in the 1970s revealed little metamorphic rock overall with a preponderance of sheared granite and granodiorite making up 60% of basement rock.
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The island lays claim to many "most northerly" UK titles: the tiny settlement of Skaw in the north-east of the island is the northernmost settlement in the UK; Haroldswick is the site of Britain's most northerly church; the Muckle Flugga lighthouse, just off the far north of Unst, was opened in 1858 and is the most northerly lighthouse in the UK, situated close to Out Stack, the most northerly rock in the UK. Western Norway is 300 km away. The islands of Unst and Fetlar are mainly formed of ultramafic and mafic igneous rocks which are interpreted to form part of an ophiolite,Unst on the Scottish Geology website maintained by the Hunterian Museum a section of oceanic crust from the Iapetus ocean which was destroyed during the Caledonian orogeny. Unst was once the location of several chromite quarries, one of which was served by the now- disused Hagdale Chromate Railway from 1907 to 1937.Simms, Wilfred F. (1997).
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The Mount Edziza and Level Mountain complexes have shelves of older lava with elevations more than and have been zones of volcanic activity long enough that their geothermal activities might have had effects on movements of the Cordilleran Ice Sheet much like the Grímsvötn caldera in Iceland, which has been a significant heat source beneath the vast Vatnajökull icecap. At the Edziza complex, most of the subglacial products were formed on top of the main lava plateau, which now rises at least in elevation above adjacent stream valleys. The Edziza complex consists of a collection of mafic subglacial products, but more unusually, including Hoodoo Mountain and Level Mountain, comprises some of the largest deposits of peralkaline felsic subglacial volcanics known. At the Edziza and Level Mountain complexes, glacier hydrology of the Cordilleran Ice Sheet was possibly dominated by a complicated interaction between drainage on the flat plateaus under relatively thinner ice and drainage within nearby steep valleys filled with much thicker ice.
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The Bentley Supergroup Volcanics are a sequence of bimodal supracrustal volcanic rocks formed during the ~1080 Warakurna Large Igneous Province, and are widely considered comagmatic with the mafic to ultramafic Giles Complex intrusions. The Bentley Supergroup is composed primarily of bimodal volcanism, with several hundred-metres thicknesses each of alternating rhyolite and basaltic volcanism adding up to several kilometres true thickness in the area of the Warburton Range to the southwest of the Palgrave caldera. The Bentley Supergroup is divided into the Cassidy Group, Pussycat Group and Tollu Group. The prevailing theory of the formation of the Bentley Supergroup is that the Warakurna Large Igneous Province, primarily represented by the Giles Complex intruding into the lower crust, breached the crust and erupted voluminous basaltic lava flows, and when enough heat had been added to the crust by the massive intrusions below, intracrustal felsic and intermediate melts were produced, forming A-type intracontinental granites of the Winburn Suite, and the felsic volcanic rocks.
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Attempts to reconstruct the craton's tectonic history have focused extensively on the east–west asymmetry. The presence of a collisional suture suggests the CSBC collided with an island arc terrane along a boundary directed north–south before 2.69 Ga. Alternatively, the Eastern Slave may be an attenuated and modified Mesoarchaean lithosphere which developed during rifting at 2.85–2.70 Ga. The mantle lithosphere under the western Slave can be 400 Ma older than that underlying the eastern Slave. Furthermore, rifting is backed up by the existence of younger arc or back-arc rocks that overly the CSBC, but make up most of the Eastern Slave. However, whether the Eastern Slave was the result of rifting or the accretion of another terrane is still up for debate. Following the 2.7 Ga rifting or accretion event, the Slave underwent large scale extension at 2680 Ma resulting in the formation of the > 400x800 km Burwash Basin, widespread mafic sills, and other younger turbidites along the northwestern margin.
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Approximately 58,000 ounces of lode gold and 4000 ounces of placer gold have come from the Ketchikan district, consisting of Dall, Prince of Wales, Revillagigedo, and smaller islands, as well some mainland, in the southernmost-part of Alaska. Numerous historical lode mines and prospects for base metals, uranium, rare earth elements (REE's), iron, and platinum group elements (PGE's), as well as gold exist in the Ketchikan district. Major gold production came from underground lode mines exploiting: gold-bearing quartz veins in metamorphic rocks (such as the Gold Standard, Sea Level, Dawson, Golden Fleece, and Goldstream mines); skarns (at the Jumbo and Kassan Peninsula copper-gold mines); zoned mafic-ultramafic plutons, as at the Salt Chuck silver-gold-copper-PGE mine; and VMS deposits such as Niblack. A high- yielding mine in Ketchikan District is the Golden Fleece Mine, located about 0.2 mile north of the north end of James Lake on Prince of Wales Island, latitude: 55.152179, longitude: -132.056635. The mine was most active from 1901 to 1905.
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Paleomagnetic studies show Kenorland was in generally low latitudes until tectonic magma-plume rifting began to occur between 2.48 Ga and 2.45 Ga. At 2.45 Ga the Baltic Shield was over the equator and was joined to Laurentia (the Canadian Shield) and both the Kola and Karelia cratons. The protracted breakup of Kenorland during the Late Neoarchaean and early Paleoproterozoic Era 2.48 to 2.10 Gya, during the Siderian and Rhyacian periods, is manifested by mafic dikes and sedimentary rift-basins and rift-margins on many continents. On early Earth, this type of bimodal deep mantle plume rifting was common in Archaean and Neoarchaean crust and continent formation. Map of Kenorland breaking up 2.3 billion years ago The geological time period surrounding the breakup of Kenorland is thought by many geologists to be the beginning of the transition point from the deep- mantle-plume method of continent formation in the Hadean to Early Archean (before the final formation of the Earth's inner core) to the subsequent two- layer core-mantle plate tectonics convection theory.
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Columbia began to fragment about 1.5–1.35 Ga, associated with continental rifting along the western margin of Laurentia (Belt-Purcell Supergroup), eastern India (Mahanadi and the Godavari), southern margin of Baltica (Telemark Supergroup), southeastern margin of Siberia (Riphean aulacogens), northwestern margin of South Africa (Kalahari Copper Belt), and northern margin of the North China Block (Zhaertai-Bayan Obo Belt). The fragmentation corresponded with widespread anorogenic magmatic activity, forming anorthosite-mangerite-charnockite- granite (AMCG) suites in North America, Baltica, Amazonia, and North China, and continued until the final breakup of the supercontinent at about 1.3–1.2 Ga, marked by the emplacement of the 1.27 Ga Mackenzie and 1.24 Ga Sudbury mafic dyke swarms in North America. Other dyke swarms associated with extensional tectonics and the break-up of Columbia include the Satakunta-Ulvö dyke swarm in Fennoscandia and the Galiwinku dyke swarm in Australia. An area around Georgetown in northern Queensland, Australia, has been suggested to consist of rocks that originally formed part of Nuna 1.7 billion years ago in what is now Northern Canada.
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Stanley (1999) One perspective of how the cratonization process might have first begun in the Archean is given by Warren B. Hamilton: > Very thick sections of mostly submarine mafic, and subordinate ultramafic, > volcanic rocks, and mostly younger subaerial and submarine felsic volcanic > rocks and sediments were oppressed into complex synforms between rising > young domiform felsic batholiths mobilized by hydrous partial melting in the > lower crust. Upper-crust granite-and-greenstone terrains underwent moderate > regional shortening, decoupled from the lower crust, during compositional > inversion accompanying doming, but cratonization soon followed. Tonalitic > basement is preserved beneath some greenstone sections but supracrustal > rocks commonly give way downward to correlative or younger plutonic rocks... > Mantle plumes probably did not yet exist, and developing continents were > concentrated in cool regions. Hot-region upper mantle was partly molten, and > voluminous magmas, mostly ultramafic, erupted through many ephemeral > submarine vents and rifts focussed at the thinnest crust.... Surviving > Archean crust is from regions of cooler, and more depleted, mantle, wherein > greater stability permitted uncommonly thick volcanic accumulations from > which voluminous partial-melt, low-density felsic rocks could be > generated.
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Earth's crust (km) Continental and oceanic crust on the upper earth mantle Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is richer in silicates and aluminium minerals and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate minerals and is denser. Changes in seismic wave velocities have shown that at a certain depth (the Conrad discontinuity), there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character. The continental crust consists of various layers, with a bulk composition that is intermediate (SiO2 wt% = 60.6). The average density of continental crust is about 2.83 g/cm3, less dense than the ultramafic material that makes up the mantle, which has a density of around 3.3 g/cm3.
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Foden, 1979, p. 49 Olivine is most present in the rocks with less than 53 percent SiO2, while it is absent in the more silica-rich volcanics, characterised by the presence of biotite phenocrysts.Foden, 1979, p. 50 The mafic series also contain titanium magnetite and the trachybasalts are dominated by anorthosite-rich plagioclase.Foden, 1979, p. 51 Rubidium, strontium and phosphorus pentoxide are especially rich in the lavas from Tambora, more than the comparable ones from Mount Rinjani.Foden, 1979, p. 56 The lavas of Tambora are slightly enriched in zircon compared to those of Rinjani.Foden, 1979, p.60 The magma involved in the 1815 eruption originated in the mantle and was further modified by melts derived from subducted sediments, fluids derived from the subducted crust and crystallization processes in magma chambers. 87Sr86Sr ratios of Mount Tambora are similar to those of Mount Rinjani, but lower than those measured at Sangeang Api. Potassium levels of Tambora volcanics exceed 3 weight percent, placing them in the shoshonite range for alkaline series.
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The Sidlaws are formed from a mix of igneous and sedimentary rocks originating during the early part of the Devonian period. The Dundee Flagstones are a mix of slabby and cross-bedded sandstones with some siltstones and mudstones which interleave with the rocks of the overlying Ochil Volcanic Formation. They form the bulk of the hills along the southern margin of the range from Scotston Hill and the eastern slopes of Balkello Hill in the west, through Craigowl Hill, much of Gallow Hill, Ironside Hill and Finlarg Hill to Kincaldrum Hill in the east, together with the outlying Fothringham Hill and Carrot Hill ridge. The Dundee Flagstones were intruded by rocks of the 'Midland Valley Siluro-Devonian Mafic Intrusion Suite'; these outcrop on parts of Auchterhouse and Scotston hills, Blacklaw and West Mains hills. The Ochil Volcanics form the sometimes craggy King’s Seat, Gask Hill, Northballo and Southballo hills and the ridge north and west of Long Loch; Lundie Craigs are a significant southeast facing exposure of this formation.
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In April 2014, scientists reported finding evidence of the largest terrestrial meteor impact event to date near the Barberton Greenstone Belt. They estimated the impact occurred about 3.26 billion years ago (during the Paleoarchean era of the Archean eon of the Precambrian supereon) and that the impactor was approximately 37 to 58 kilometers (23 to 36 miles) wide, roughly five times larger than the impactor responsible for the Chicxulub crater in the Yucatán Peninsula, which was around the size of Mount Everest. The gigantic impactor was estimated to have collided with the Earth at a speed of 20 kilometers per second (12 miles per second), releasing an enormous amount of energy and triggering magnitude 10.8 earthquakes across the planet, as well as generating megatsunamis thousands of meters high. The crater from this event, if it still exists, has not yet been found. The Barberton Greenstone Belt consists of a sequence of mafic to ultramafic lavas and metasedimentary rocks emplaced and deposited between 3.5 and 3.2 Ga. The granitoid rocks were emplaced over a 500-million-year time span and can be divided into two suites: The tonalite-trondhjemite-granodiorite (TTG) suite (emplaced approximately 3.5–3.2 Ga), and the granite–monzogranite–syenite granite (GMS) suite (emplaced approximately 3.2–3.1 Ga).
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Deep-sea hydrothermal vent or black smoker The deep sea vent, or alkaline hydrothermal vent, theory posits that life may have begun at submarine hydrothermal vents, Martin and Russell have suggested > that life evolved in structured iron monosulphide precipitates in a seepage > site hydrothermal mound at a redox, pH, and temperature gradient between > sulphide-rich hydrothermal fluid and iron(II)-containing waters of the > Hadean ocean floor. The naturally arising, three-dimensional > compartmentation observed within fossilized seepage-site metal sulphide > precipitates indicates that these inorganic compartments were the precursors > of cell walls and membranes found in free-living prokaryotes. The known > capability of FeS and NiS to catalyze the synthesis of the acetyl- > methylsulphide from carbon monoxide and methylsulphide, constituents of > hydrothermal fluid, indicates that pre-biotic syntheses occurred at the > inner surfaces of these metal-sulphide-walled compartments,... These form where hydrogen-rich fluids emerge from below the sea floor, as a result of serpentinization of ultra-mafic olivine with seawater and a pH interface with carbon dioxide-rich ocean water. The vents form a sustained chemical energy source derived from redox reactions, in which electron donors (molecular hydrogen) react with electron acceptors (carbon dioxide); see Iron–sulfur world theory.
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The first stage of the formation of the Klamath mountains was arc magmatism on the western coast of North America which resulted in the formation of the Western Hayfork Terrane. Once the Western Hayfork Terrane was formed (and had subsequently stopped forming) the region was intruded by mafic dikes attributed to some form of extension at approximately 160 Ma. Once extension ceased in the area, compression began again, resulting in the closure of a very small back arc basin produced by the extension and accreted the ophiolite sequences seen in the Klamath Mountains from the Nevadan Orogeny time (Josephine Ophiolite at 155 Ma). Continued convergence in the Klamath Mountains region would eventually lead to the emplacement of dikes and sills within the Josephine Ophiolite at approximately 153 Ma. The youngest of the accretionary ophiolite sequence in the Klamath Mountains appears to be the Josephine Ophoilite, which is dated to be about 155 to 150 Ma in age using both argon-argon (Ar-Ar) and lead-uranium (Pb-U) methods. Rather than being thrust on top of North America, the Josephine Ophiolite was accreted through a different process that involved being thrust underneath of North America and then eventually being exhumed at the surface.
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Because the BHT is covered by Phanerozoic rocks, its extent is uncertain and only known from aeromagnetic data and drill cores. To the south it is truncated by the Snowbird Tectonic Zone; to the north it is delimited by the Great Slave Lake Shear Zone; in the east it is separated from the Rae Craton by the 1.99–1.9 Ga Taltson Magmatic Zone; and in the west it is separated from the Nova Terrane by the magmatic rock of the Ksituan High. In its southern end the BHT is intruded by the Peace River Arch, a cratonic uplift active since the Proterozoic. defined the BHT as a broad, north-trending region of areomagnetic anomalies. Drill cores from this region returned Zircon ages 2.324–1.993 Ga with occurrences of metaplutonic rocks in the range 1.999–1.993 Ga. From this Ross concluded that the BHT formed 2.32–2.0 Ga and was affected by a thermal-magnetic event 2.0–1.9 Ga. The inherited age of the Proterzoic basement rocks is 2.4–2.1 Ga. The Rae Craton is of similar age and isotopic signature which suggest it and the BHT formed a single crustal entity at 2.4 Ga. 2.34 Ga mafic to ultramafic rocks between BHT och Rae indicate separation by this time.
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