Granite-like, or felsic, rocks in northwest Canada dating back to the Earth's earliest era seem to have different compositions from the felsic rocks at the cores of the continents.
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Molten rock that glows red is probably in the felsic temperature range.
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One type of magma, called felsic or rhyolitic, is about 21 percent to 2472 percent silicon dioxide; its temperature is roughly 1,112 to 1,472 degrees Fahrenheit.
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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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O'Neil's study adds evidence to that idea, and suggests that later on in Earth's history the planet could have developed granites, the felsic crusts, most likely as a result of emerging plate tectonics, maybe around 3 or so billion years ago.
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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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"Given the predicted high flux of meteorites in the late Hadean," the hellish era just after the Earth formed, from 4.6 billion to 4.0 billion years ago, "impact melting may have been the predominant mechanism that generated Hadean felsic rocks," the authors write in the new paper published in Nature Geoscience.
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"The idea of making felsic melts by large or giant impacts seems plausible considering the high-energy nature of these events and the pockmarked ancient surfaces of other inner Solar System planets and moons," Balz Kamber from Trinity College Dublin, who was not involved in the study, said in a statement.
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Fig. 1. A schematic diagram showing the formation environment of Archean felsic volcanic rocks. Modified from Giles (1980). Felsic eruption forms felsic volcanic rocks near the volcano and a spectrum of alt= Archean felsic volcanic rocks are felsic volcanic rocks that were formed in the Archean Eon (4 to 2.5 billion years ago).Cohen, K.M., Finney, S.M., Gibbard, P.L., Fan, J.-X. (2013).
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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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Archean felsic volcanic rocks is important to deduce absolute age of the rock units in greenstone belts. Felsic eruptions are episodic so that the felsic volcanic layers are distinctive stratigraphic units. Also, felsic volcanic rocks are distributed vastly across long distances because of its extensive deposition. However, the rock sequences of greenstone belts are commonly disputed by later deformation, such as regional folding or intrusion of granitoids.
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By identifying these felsic sequences and dating their time of formation, stratigraphic units of different locations can be correlated despite the obstacles or discontinuity in between felsic volcanic units.
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Thus, felsic volcanic rocks are rare members in the Archean terranes. Archean felsic volcanic activities commonly occur in submarine environments. The composition of Archean felsic volcanic rocks are equivalent to a spectrum between dacite and rhyolite. They can be distinguished by their mineral assemblages, rock chemistry and rock layer relationship in the sequences.
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Revealing the relationship between Archean felsic volcanic rocks and the granitoids may be difficult. It is because weathering alters the geochemical signatures of the felsic rocks above the Earth's surface. The earliest weathering record can be traced back to 3.8 Ga during Eoarchean. Potassium is enriched but sodium is depleted in these weathered felsic rocks.
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Archean felsic volcanic rocks are utilised to date the timing of geological events and match distant rock units in separated Archean cratons. They are important to reconstruct Archean geological environments. Felsic granitoids are the most prevalent rock type in Archean terranes. These intrusive felsic igneous rocks include TTG suites (Tonalite-Trondhjemite- Granodiorite) that contributes over half the portion of Archean cratons.
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In Archean, underwater eruptions of felsic lava were common. Submarine eruption is evident by coarse volcanic breccia formed in situ, hyaloclastite or underwater pyroclastic deposits (clastic rock, composed of tephra only). Since felsic magma is viscous, volcanic eruptions that form dacite or rhyolite are explosive and violent. The Archean felsic eruption may be assigned to Vesuvius eruption type in the present day.
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Records of Archean felsic volcanic rocks shows a peculiar trend. The eruption of felsic volcanic rocks and plutonic activities in Archean are largely synchronised as show in overlapping zircon ages. On contrary, the chemical compositions of some felsic volcanic rocks are similar to that of GMS but they are much older than GMS. For example, a GMS- like rhyolite unit in the Abitibi Greenstone Belt (abnormally more enriched in potassium and heavy rare-earth elements than other Archean felsic volcanic rocks) has no plutonic equivalent in the same period.
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The mountain is made up of non-alkali felsic rock and pyroclasitic flows.
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Precambrian rock in Voyageurs National park, which straddles the Wabigoon and Quetico subprovinces. The Wabigoon subprovince is a formerly active volcanic island chain, made up of metavolcanic-metasedimentary intrusions. These metamorphosed rocks are volcanically derived greenstone belts, and are surrounded and cut by granitic plutons and batholiths. The subprovince's greenstone belts consist of felsic volcanics, felsic batholiths and felsic plutons aged from 3,000 to 2,670 million years old.
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The Wawa subprovince is a formerly active volcanic island chain, consisting of metamorphosed greenstone belts which are surrounded by and cut by granitic plutons and batholiths. These greenstone belts consist of felsic volcanics, felsic batholiths, felsic plutons and sediments aged from 2,700 to 2,670 million years old. The predominate rock type is a white, coarse-grained, foliated hornblende tonalite. Minerals in the tonalite are quartz, plagioclase, alkali feldspar and hornblende.
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Crossbedding is pervasive. Flattened felsic clasts may be metamorphosed pumice.Simmons et al. 2011, p.
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Felsic magmatism ceases and accretion of island arcs occurs in the Central Metasedimentary Belt.
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Feldspar-phyric basalt lava flows are normally pillowed. Pyroclastic deposits, quartz-phyric and feldspar-felsic rocks are also present. The largest of the less common felsic lava flows is located between Link Lake and Turtle Lake. It is long and less than thick.
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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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Obsidian is formed from quickly cooled lava, which is the parent material.M E Malainey. Consumer's Guide to Archaeological Science: Analytical Techniques, Springer, 2010 Extrusive formation of obsidian may occur when felsic lava cools rapidly at the edges of a felsic lava flow or volcanic dome, or when lava cools during sudden contact with water or air. Intrusive formation of obsidian may occur when felsic lava cools along the edges of a dike.
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The gold bearing veins cut through felsic intrusions and country rock, dipping south and striking NE.
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They have implications in finding how the felsic volcanic rocks were formed and related to the granitoids.
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Sills and dikes are widespread throughout the Arsenic Lake Formation and range in composition from ultramafic to felsic.
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Later, felsic volcanic rocks were emplaced within the caldera and the Voon ignimbrite buried parts of the tholeiite.
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The Eastern Felsic Complex (EFC), in northeastern Ascension has a ring-shape geometry with felsic flows and pyroclastic deposits. Rocks in the EFC constitute trachyte, rhyolite and formations such as lava domes and thick flows. Pyroclastics exhibit a blend of ash and pumice. These rocks formed approximately 517,000 years ago.
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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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Presence of the above lithologies is an indicator of paleo-environment because, (1) The Amitsoq gneiss often shows graded felsic clast units, which means a derivation from felsic volcanic or felsic volcano-sedimentary rock. (2) Presence of pillow-structured lava and breccia indicated that there were liquid water in eoarchean ages. (3) Banded Iron Formation (BIF), with minor metachert unit, is an indicator for coeval deposition of aqueous clastic and chemical sediment. Subsequent U-Pb zircon- dating program has been done to test the rock ages.
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The Big Dan Shear Zone was contemporaneous to volcanism due to the higher density of felsic dikes situated at the shear zone. These dikes are only present north of the Link Lake Deformation Zone, therefore they may be subvolcanic feeders to the felsic lava flows to the south. Renewed tectonism along the Big Dan Shear Zone displaced sediments east of the Ontario Northland Railway. This phase of tectonic activity along the Big Dan Shear Zone also displaced felsic dikes north of the shear zone.
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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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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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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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In the middle of the intrusive body, the grain size of quartz phenocrysts averages roughly , but become smaller towards the edge of the intrusion. Broken fragmental rocks, interpreted to be carapace breccia, are exposed along the western margin of the intrusion. Exposed near a minor felsic lava dome is a fine grained, quartz-phyric felsic rock that may represent a rhyolite lava flow. An igneous body, interpreted to be a subvolcanic intrusion, is exposed approximately to the northwest and might have formed during the same magmatic event as the felsic dome.
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A unique characteristic of the peralkaline felsic lava flows produced during this stage of activity is that although they were high in silica content, the flows were overly fluid in nature. This is because the peralkaline content decreased the viscosity of the flows a minimum of 10–30 times over that of calc-alkaline felsic flows. As a result of this fludity, the peralkaline felsic lava flows were able to form small-scale folds and diameter lava tubes. The liquidus temperatures of these flows were in excess of with viscosities as low as 100,000 poise.
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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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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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The ICS International Chronostratigraphic Chart. Episodes 36, 199-204. The term "felsic" means that the rocks have silica content of 62–78%. Given that the Earth formed at ~4.5 billion year ago, Archean felsic volcanic rocks provide clues on the Earth's first volcanic activities on the Earth's surface started 500 million years after the Earth's formation.
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The meaning of "felsic" refers to high silica (SiO2) content from 62 to 78 wt% in rock. In terms of mineralogy, the felsic volcanic rocks are rich in feldspar and quartz. A typical mineral assemblage is quartz + feldspar (albite/oligoclase) + amphibole (chlorite) + micas (biotite and/or muscovite). The mineralogy seems similar with modern rhyolites and dacites.
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The volcanics are aphanitic, whereas some exhibits porphyritic texture that certain larger minerals (phenocrysts) are visible by eyes. alt= Felsic volcanic rocks also include felsic tuff that was formed when tephra was consolidated. Tuff is composed of volcanic ash, glass shards and lithic fragments. Reported eutaxitic tuff from Superior Province, Canada (Figure 3), contains lenticular fiamme.
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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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Volcanic vents composed of felsic rocks are thought to have been located at the iron-bearing Sherman Mine, the former Temagami garbage dump and adjacent to the Milne Townsite. Remnants of a large volcanic vent are present west of Sherman Mine, including the existence of two felsic lava flows that outcrop between Link Lake and Turtle Lake. The aspect of the most extensive felsic lava flow indicates that the volcanic vent they erupted from was adjacent to the western portion of Link Lake. Additionally, differentiation of facies and directions in which the lava traveled exist in course grained, resedimented conglomerate.
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Ultramafic rocks of the Hooggenoeg Formation were most likely not parental for the felsic rocks. Subduction processes may have played a role in the generation of the felsic rocks, but a tectonic setting for the ultramafic rocks remains uncertain. The felsic units of the Hooggenoeg Formation are very similar to those of the Panorama Formation of the Early Archaean Coppin Gap greenstone belt of Western Australia (See Yilgarn Craton). Similarities in geological setting, petrography, and geochemical (trace element in particular) characteristics suggest a possible genetic relation between the two formations and support the theory that a combined continent Vaalbara existed ~3.45 Ga.
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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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The Discovery hotspot appears to have erupted two separate sets of magmas with distinct compositions, similar to the Tristan da Cunha-Gough Island hotspot. The composition of the Discovery Seamounts rocks has been compared to Gough Island. The more felsic rocks at Discovery appear to be derived from magma chamber processes, similar to felsic rocks at other Atlantic Ocean islands.
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Plagioclase is commonly the only feldspar phyric phase in the felsic to intermediate volcanic clasts, including lapilli and vitric tuff and probable ash-flow tuff.
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This thick rock unit was formed during a period of volcanic activity between 1,900,000 and 500,000 years ago. It consists of subvolcanic intrusions of a partly preserved volcanic vent and felsic volcanic rocks that were erupted from the vent. The eastern portion of The Devastator Assemblage comprises the partly preserved vent and felsic volcanic rocks while the western portion consists of crudely layered tephra.
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2, pp. 365–377. is characterized by ultramafic massive and pillow lavas, a trondhjemitic suite of silicified felsic intrusive and flow banded rocks, and sedimentary chert beds. Veins of felsic, chert and ultramafic material intrude the belt. The depositional environment is thought to be a shoaling shallow sea in which the Hooggenoeg Formation has been deposited in a west-block down, listric faulted, synsedimentary setting.
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The stratovolcano, which is the only large central volcano in its part of Iceland, has many pyroclastic cones on its flanks. Upper-flank craters produced intermediate to felsic materials, while lower-flank craters produced basaltic lava flows. Several holocene eruptions have originated from the summit crater and have produced felsic material. The latest eruption took place 200 AD ± 150 years, and erupted approximately of volcanic material.
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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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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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Exploration for copper is continuing in several areas around Ravensthorpe, Balagundi, in the Yandall Belt, and the Duketon Belt, where large felsic volcanic packages are known to exist.
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This consists of a long ridge of trachytic lava domes and flows and basaltic and trachybasaltic cinder cones that extend south from the felsic Itcha Range volcanic complex.
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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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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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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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These dark compressed pyroclastics have been interpreted to be pumice. Some of the subsequence pyroclastic deposits contain fragments of pyrite and quartz, suggesting that discharged sulfide hydrothermal activity took place throughout the volcanic source area. Resedimented felsic, epiclastic and turbiditic sediments compose the Turtle Lake Formation. The base of this formation consists of a heterolithic, volcaniclastic, matrix-supported conglomerate unit that overlies felsic lava flows and pillowed, calc-alkaline basalts of the Link Lake Formation.
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In geology, a cupola is an upward protrusion from the roof of a large igneous intrusion, such as a batholith. It may also refer to small outlying igneous bodies which may connect at depth with larger igneous masses. Cupola-type magma chambers might form above larger basaltic magma bodies and differentiate to create intermediate or felsic magmas, which in turn may reach the surface to produce small eruptions of intermediate or felsic lava.
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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 slopes of the peak are highly unstable, consisting of weak, hydrothermally altered felsic rocks. There have been many recent debris flows which have flowed down into the Meager Creek drainage.
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Structureless hyaloclastite is commonly found in Archean felsic volcanic rocks. In submarine environments, water quenches and cools lava rapidly during volcanic eruption. The flow is fragmented and form glassy volcanic breccia.
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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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An example is the north-south trending Big Dan Shear Zone situated near the former garbage dump of Temagami. The felsic dikes near this zone are interpreted to represent a subvolcanic feeder system to the overlying felsic volcanic rocks. It is probable that the dikes maintained a former zone of weakness now demonstrated by the shear zones. Renewed tectonic activity along the Big Dan Shear Zone is manifested by offset of clastic sediments east of the Ontario Northland Railway.
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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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The glauconitic siltstone has resulted from a high level flooding event in the Bambuí Basin. The sedimentary provenance is from supracrustal felsic elements on continental margin environment with acid magmatic arc (foreland basin).
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Felsic magmatism dominates this time period. The cause of the magmatism is debated between an extensional setting or a continental-margin arc. The name is in relation to the ensuing orogeny and metamorphism.
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This phase of tectonic activity displaced felsic dikes north of the exposed part of this shear zone. However, considerable displacement of the dikes at this location is unknown. The most recent phase of tectonic activity along the Big Dan Shear Zone resulted in the displacement of a Proterozoic dike composed of diabase, which intersects the zone. A similar abundance of felsic dikes are adjacent to Arsenic Lake just west of Highway 11, indicating similar repetitive tectonism also occurred along that structural zone.
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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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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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Researchers believe this because the trace element geochemistry of the bentonite shows that its source was a felsic calc-alkalic magmatic source, which is characteristic of volcanism from a continental crust destructive plate margin setting.
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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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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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This is in turn overlain by stringy-beef textured recrystallised disseminated ore zones containing retrogressed metamorphic olivine and distinctive bladed anthophyllite. The structural overprint of the ultramafics and orebody by deformation during prograde metamorphism is a matter of debate, however the ductile nature of the deformation has affected the ultramafic CUU heterogenously and contrasts with the felsic footwall. The felsic footwall is subject to a pronounced stretching lineation which increases in intensity to the north. The lineation orientation is a uniform 65 degrees toward 120 degrees.
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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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The alternate spelling, felspar, has fallen out of use. The term 'felsic', meaning light colored minerals such as quartz and feldspars, is an acronymic word derived from feldspar and silica, unrelated to the redundant spelling 'felspar'.
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Because certain lithologies can be correlated through the Link Lake Deformation Zone, it is unlikely that the lack of felsic dikes south of the former town dump area is an expression of displacement along the deformation zone.
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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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Exposed along the Sherman Mine railroad west of the former Milne sawmill lumber yard is a porphyritic body composed of quartz-feldspar. It is unknown if this igneous rock is a rhyolitic lava flow or an intrusion. Several north-trending felsic dikes, composed mainly of feldspar and quartz-feldspar, are located north of the former Temagami garbage dump. These dikes are not known to extend across the Link Lake Deformation Zone, suggesting that they might represent the feeders of a minor volcanic vent, manifest now by felsic lava flows.
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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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In the Archean Eon Western Massachusetts and Vermont were the eastern edge of Laurentia (now the Canadian Shield). Laurentia is believed to have originated at the end of the Hadean, making it one of the oldest regions with continental crust, as evidenced by the discovery of Acasta Gneiss in Canada. At the end of the Hadean massive eruptions of felsic lava became cool enough to form permanent crust. The felsic nature of Laurentia allowed it to float over the denser ocean basins that surrounded it, so it was not submerged under the then- forming oceans.
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By the Pliocene epoch, radially directed alpine glaciers had eroded away much of the bimodal stratovolcano cap, leaving behind a series of U-shaped valleys with intervening ridges that comprise the Level Mountain Range. This dissection of the bimodal stratovolcano was followed by the felsic dome-forming stage. Eruptions of felsic magma were predominantly viscous during this stage of activity, resulting in the magma piling up thick around volcanic vents to create a series of lava domes. Individual domes grew up to in the glacially eroded core of the bimodal stratovolcano.
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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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Eruptions became more viscous during the explosive phase, followed by more viscosity during the post-explosive phase. As a result, the volume of erupted material became smaller over time. The increasing viscousness of felsic lava during the shield-building stage suggests a maturing plumbing system underneath the Itcha Range, which may have consisted of multiple, isolated, cupola-type magma chambers. Geologic map of the Itcha Range showing stages of development A 900,000‑year‑long period of quiescence followed after the felsic shield-building stage, during which time erosion ate away at the shield's gentle slopes.
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Felsic or silicic lavas such as rhyolite and dacite typically form lava spines, lava domes or "coulees" (which are thick, short lava flows) and are associated with pyroclastic (fragmental) deposits. Most silicic lava flows are extremely viscous, and typically fragment as they extrude, producing blocky autobreccias. The high viscosity and strength are the result of their chemistry, which is high in silica, aluminium, potassium, sodium, and calcium, forming a polymerized liquid rich in feldspar and quartz, and thus has a higher viscosity than other magma types. Felsic magmas can erupt at temperatures as low as .
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The similarity of the resulting term felsic to the German felsig, "rocky" (from Fels, "rock"), is purely accidental. Feldspar is linked to German. It is a borrowing of Feldspat. The link is therefore to German Feld, meaning "field".
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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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These geological observations indicate that the trachyte is an intrusive body, being the oldest body of the felsic alkaline magmatism of this area, and is clearly different from the lava flows overlying the eroded surface of the syenite.
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Fig 6. Possible relationship 2 of Archean felsic volcanic rocks and granitoids. GMS and TTG may have intruded the crust at the same time. Yet, GMS was concentrated at the upper crust and TTG at deeper intermediate crust.
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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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The mechanism to generate a large amount of felsic crust usually requires the presence of water ocean and plate tectonics, implying that habitable condition had existed on early Venus. However, the nature of tessera terrains is far from certain.
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TTG-Felsic crusts formed in multiple episodes. By U-Pb zircon geochronology, the fourfold episodic TTGs were yielded 3.76 Ga, 3.66 Ga, 3.5–3.4 Ga and 3.35 Ga. The surrounding TTG are suggested to be an indicator for paleo subduction systems.
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It is formed by felsic lava. Rincón de la Vieja is one of six active Costa Rican volcanoes: the others are Poás, Irazú, Miravalles, Arenal, and Turrialba. As of 2020, only Rincon de la Vieja, Turrialba and Poas are considered active.
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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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Beaverdam Creek drains of area. The confluence is at the border of felsic gneiss, but the stream then flows over Falls Leucogneiss. The watershed receives an average of 46.6 in/year of precipitation and has a wetness index of 390.31.
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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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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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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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Lake Nipisso and Lake Manitou to the east define the Manitou-Nipisso geological area, which is part of the Polycyclic Belt of the Grenville Province. The bedrock of the lake is in the Manitou Gneiss Complex, and is mostly composed of quartz–feldspar gneiss and hornblende–biotite gneiss. A 1997 study of a mineral property about 2/3 of the way up the east shore found most of the units present in the Nipisso-Manitou geological complex, including felsic gneisses, abundant gabbro and minor granitoid intrusives. The property had mineralized ultramafic dikes associated with a brecciated felsic pipe.
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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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A lithophysa (plural lithophysae, from Greek lithos "stone" + physan "to blow")What Are Lithophysae? is a felsic volcanic rock with a small spherulitic cavity and concentric chambers. Its shape is spherical or lenticular. These rocks are usually found within obsidian or rhyolite.
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Masago, H., 2000, Metamorphic petrology of the Barchi-Kol metabasites, western Kokchetav ultrahigh-pressure–high-pressure massif, northern Kazakhstan: The Island Arc, v. 9, p. 358–378. Most felsic UHP rocks have undergone extensive retrograde metamorphism and preserve little or no UHP record.
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Cerro Bonete is a volcano in Sur Lipez. It is part of the Cordillera de Lipez and is high. The volcano is of Miocene age and formed by potassium-rich felsic rocks. It is associated with the 15 mya South Lípez ignimbrites.
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"Structure, stratigraphy, and hydrocarbon system of a Pennsylvanian pull-apart basin in north-central Texas." AAPG bulletin 86, no. 1 (2002): 1–20. The shallow extensional regime of pull-apart basins also facilitates the emplacement of felsic intrusive rocks with high copper mineralisation.
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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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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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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 Itcha Range as seen from the south with a forested volcanic cone in the foreground The composition of the volcanoes' magma has changed significantly with time as they grow over the hotspot and migrate away. Volcanic activity 14.5 to 3.0 million years ago was predominately felsic, producing large volumes of rhyolite and trachyte lava. This can be explained by the presence of thick granitic structures under these volcanoes, which have been tectonically compressed from being near the North American Plate margin. A unique characteristic of the felsic lava flows is that although they were high in silica content, the flows were overly fluid in nature.
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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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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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Its fine texture and felsic components allow for good knapped pieces, much like working chert, producing conchoidal fracture. Dendritic manganese oxides such as pyrolusite and/or iron oxides such as limonite may precipitate along rock crevices, giving some rock chunk surfaces multicolored or arborescent patterned textures.
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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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Granite is an igneous intrusive rock (crystallized at depth), with felsic composition (rich in silica and predominately quartz plus potassium-rich feldspar plus sodium-rich plagioclase) and phaneritic, subeuhedral texture (minerals are visible to the unaided eye and commonly some of them retain original crystallographic shapes).
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In Precambrian section was made up of felsic-intermediate granite with the inclusion of greenstones and ophiolites, where the Paleozoic section consists of mainly potassium- and sodium-deficient extrusive rocks. The basalts in the basement which indicated trapped late Paleozoic oceanic crust that came from the mantle.
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Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8). Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures.
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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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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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Tungsten ore is a rock from which the element tungsten can be economically extracted. The ore minerals of tungsten include wolframite, scheelite, and ferberite. Tungsten is used for making many alloys. Tungsten ore deposits are predominantly magmatic or hydrothermal in origin and are associated with felsic igneous intrusions.
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The ratio of gallium to aluminium is high, as is the ratio of iron to magnesium. There are lower levels of calcium and strontium. By using Ga/Al ratio, fractionated felsic I or S-type granites can overlap in apparent composition. Enriched alkalis include sodium, potassium, rubidium and caesium.
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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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During the Mesoproterozoic Era, another rifting phase began.Deb, M., Talwar, A.K., Tewari, A., Banerjee, A.K., 1995. Bimodal volcanism in South Delhi fold belt: a suite of differentiated felsic lava at Jharivav, north Gujarat. In: Sinha-Roy, S., Gupta, K.R. (Eds.), Continental Crust of NW and Central India. Geol. Soc.
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A number of volcanic features have been found that suggests the volcano was located west of Sherman Mine. At least two outcrops of felsic lava flows exist between Turtle Lake and Link Lake, the largest of which indicates that its volcanic vent existed at the western end of Link Lake.Exploration Potential for Base and Precious Metal Mineralization in Part of Strathy Township, Temagami Area The existence of facies changes and remnants of lava movement exposed in the wedge of the Turtle Lake Formation are likely further indications that the volcano was located west of Link Lake. Also, jagged felsic tuffs exist in feldspar-phyric pyroclastic deposits exposed in the Sherman Mine area.
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Felsic volcanic rock flanks the basin in the southwest and it is fragmented by numerous small faults. The Sharon Syenite, exposed just south of Franklin on I-495 indicates this, with a high-degree of fracturing. In fact, an inlier of Dedham Granite splits the formation in two in the southwest.
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In rare cases, felsic rocks become sulfur saturated and form sulfide segregations. In this case, the typical result is a disseminated form of sulfide mineral, usually a mixture of pyrrhotite, pyrite and chalcopyrite, forming copper mineralisation. It is very rare but not unknown to see cumulate sulfide rocks in granitic intrusions.
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On western Eyre Peninsula, the Coulta Subdomain merges with the Nuyts Subdomain which is dominated by variably deformed ca. 1670–1610 Ma granitoids, mafics and felsic volcanics. Deformation is attributed to the Kalaran Orogeny which generated a major fold belt or shear zone, the Fowler Shear Zone, ca. 1600–1540 Ma.
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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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Cummingtonite is commonly found in metamorphosed magnesium-rich rocks and occurs in amphibolites. Usually it coexists with hornblende or actinolite, magnesium clinochlore chlorite, talc, serpentine-antigorite minerals or metamorphic pyroxene. Magnesium-rich cummingtonite can also coexist with anthophyllite. Cummingtonite has also been found in some felsic volcanic rocks such as dacites.
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It has intruded dikes, plugs and xenoliths into metasediment. Albert Edward Granite is coarser, with pink K-feldspar megacrysts and green-brown biotite. There are also small amounts of carboniferous diorite. Towards the northwest of the lake, the area between the Hauroko Burn and the Hay River has dioritic, felsic dykes.
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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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Beddgelert Fault First reported in a Memoir of the British Geological Survey activity ref. Ramsay 1881. It is a SW-NE trending volcanotectonic fault in North Wales that formed part of a graben system within the collapsed Snowdon caldera structure. It was a focus for later felsic intrusions and hydrothermal activity.
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These felsic volcanics are understood to have been created by fractionation of mainly alkali basalt magma in crustal reservoirs. An area of continental rifting, such as the Northern Cordilleran Volcanic Province, would aid the formation of high-level reservoirs of capable size and thermal activity to maintain long-lived fractionation.
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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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Pillow lavas are commonly of basaltic composition, although pillows formed of komatiite, picrite, boninite, basaltic andesite, andesite, dacite or even rhyolite are known. In general, the more felsic the composition (richer in silica - resulting in an Intermediate composition), the larger the pillows, due to the increase in viscosity of the erupting lava.
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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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Explosive eruptions during this stage of activity deposited basalt agglomerates, ash fall and ash flow tuffs. Peralkaline felsic lava flows reached long and thick. The eruptive products of the bimodal stratovolcano stage cover an area roughly long and wide. Peralkalinity had remarkable effects on lava morphology and mineralogy during the bimodal stratovolcano stage.
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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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Felsic gneiss and granite migmatite, interlayered with supracrustal rocks and intruded by granodiorite, is intercalated in places with the supracrustal rocks of the greenstone belt. It is suggested that the likely origin for this unit is an ancient basement or earlier supracrustal succession tectonically interleaved as thrust splinters into the South Pass supracrustals.
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Granite rock in the cliff of Gros la Tête on Aride Island, Seychelles. The thin (1–3 cm wide) brighter layers are quartz veins, formed during the late stages of crystallization of granitic magmas. They are sometimes called "hydrothermal veins". Quartz is a defining constituent of granite and other felsic igneous rocks.
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Submarine rhyolitic flows were widespread in Archean but it is uncommon in the modern volcanic environment. Viscous felsic eruption often causes pyroclastic flow (hot, dense gas with volcanic fragments) instead of fluid lava flow. However, if the rhyolitic lava is still molten during eruption, it can behave and flow like fluid flow.
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Artifact density was assessed using GIS and statistical correlations, and it was determined that the stratification of larger artifacts remaining on the surface while smaller artifacts had been pushed below could be attributed to trees falling and disrupting the geomorphology of the site. Lithic samples of on and off-site materials from the excavation were also used for geochemical and petrological analysis, conducted independently. Excavation of the Two Dogs Site yielded 32,904 artifacts in total, which were found to mostly be dacite with some quartz and other materials appearing at significantly lower frequencies. Petrographic analysis indicated that all samples of local lithic materials were felsic volcanic rocks, and the samples of off-site lithics were found to be felsic volcanic siltstones.
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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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2nd Edition, page 381. These granites are produced by partial melting of refractory lithology such as granulites in the lower continental crust at high thermal gradients. This leads to significant extraction of hydrous felsic melts from granulite-facies resitites. A-type granites occur in the Koettlitz Glacier Alkaline Province in the Royal Society Range, Antarctica.
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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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Rhyolite ( ) is an igneous, volcanic rock, of felsic (silica-rich) composition (typically > 69% SiO2 – see the TAS classification). It may have any texture from glassy to aphanitic to porphyritic. The mineral assemblage is usually quartz, sanidine and plagioclase (in a ratio > 2:1 – see the QAPF diagram). Biotite and hornblende are common accessory minerals.
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Each element has a different partition coefficient, and therefore fractionates into solid and liquid phases distinctly. These concepts are also applicable to metamorphic and sedimentary petrology. In igneous rocks, particularly in felsic melts, the following observations apply: anomalies in europium are dominated by the crystallization of feldspars. Hornblende, controls the enrichment of MREE compared to LREE and HREE.
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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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Sugarloaf in winter from Atholville. The geological base of Atholville is composed of several rock types. North of Notre-Dame Street in the lowest area there are Clastic rocks from the Campbellton formation.Bedrock Geology of New Brunswick, New Brunswick government, consulted on August 19, 2012 Between this street and Highway 11 are Felsic rocks from the Dalhousie group.
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Poquessing Creek starts out flowing on a bedrock of felsic gneiss, from the Cambrian, consisting of quartz. microcline, pyroxene, and biotite, buff to pink color and fine to medium grained. Then it flows into a region of the Wissahickon Formation, from the Paleozoic, a schist, a metamorphic rock containing garnet, staurolite, kyanite, and sillimanite. Varieties include oligoclase-mica schist.
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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 petrological variations of the Ordovician felsic volcanic rocks of the Tetagouche Group, New Brunswick The only rocks that do not seem to be related to the caldera are scattered dikes and small effusive flows of the Taylor Brook rhyolites, the latter of which probably issued from parasitic vents on the outer margins of the caldera.
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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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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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Spherulitic texture is the result of cooling and nucleation of material in a magma which has achieved supersaturation in the crystal component. Thus it is often a subsolidus process in supercooler felsic rocks. Often, two minerals will grow together in the spherulite. Axiolitic texture results from spherulitic growth along fractures in volcanic glass, often from invasion of water.
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Slower cooling forms microscopic crystals in the lava and results in textures such as flow foliations, spherulitic, nodular, and lithophysal structures. Some rhyolite is highly vesicular pumice. Many eruptions of rhyolite are highly explosive and the deposits may consist of fallout tephra/tuff or of ignimbrites. Eruptions of rhyolite are relatively rare compared to eruptions of less felsic lavas.
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These subaqueous lava lakes are large units with a change in grain size from coarse to fine grained and a hyaloclastite top. The Kiwanis (Norands) intrusion, a high-level synvolcanic magma chamber, intrudes felsic rocks, and is in turn cross-cut by basaltic dikes and sills. The Glenwood fault forms the eastern margin of the New Senator Caldera.
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The Sturgeon Lake Caldera contains a well preserved north facing homoclinal chain of greenschist facies metamorphosed intrusive, volcanic, and sedimentary layers. This piecemeal caldera complex includes nearly of major subaqueously deposited intracaldera fill. Episodes of subaerial and subaqueous explosive felsic volcanism created rhyodacitic to rhyolitic tuffs and lapilli tuffs. The caldera complex lies in the Wabigoon greenstone belt.
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Approaching the CUU body, the lineation breaks down into a zone of heavy boudinage and oblique shear with a pronounced C-S shear fabric, especially in the remobilised massive sulfides and at the leading edge of the keel structure. This is interpreted to occur due to competency contrast between the felsic footwall and the ultramafic unit.
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Extensional tectonic activity followed the Laramide Orogeny and was accompanied by voluminous felsic volcanic eruptions. Numerous low-angle normal faults formed during this time. These faults have been particularly important in the Rosemont area. The extensional tectonics eventually produced the large- scale block faulting that produced the present Basin and Range Province throughout the southwestern United States.
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Longgang belongs to a group of volcanoes in the Changbai Mountains. Farther east lies the Changbaishan volcanic field, including Changbaishan volcano on the China-North Korea border. This volcano is the most active and dangerous in the area, and the sole volcano to erupt felsic magma. Tephra from this volcano has been found in the Longgang field.
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Effusive felsic lava flows elongate several kilometres long. During an eruption, lava continuously wells out from the vent, then starts to flow outward on the sea floor. Due to quenching, lava is rapidly fragmented to form breccia. A new lobe of lava is injected inside the breccia but it is cooled down slower and push the flow further outwards.
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Being one of the few most well-preserved Archean portions of the crust, with Archean felsic volcanic rocks, the BGB is well studied. It provides present geologic evidence of Earth during the Archean (pre-3.0 Ga). Despite the BGB being a well studied area, its tectonic evolution has been the cause of much debate. Map of South Africa.
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To the west of the Cañadón Asfalto Basin, another basin started forming in these times, the Ñirihuau Basin, characterized by the deposition of the felsic to intermediate volcanic Don Juan Formation, the basaltic Tres Picos Prieto Formation and the Huitrera Formation. In the Ñirihuau Basin, this sequence is covered by the Oligocene to Miocene Ventana Formation.Echaurren, 2017, p.
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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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The Upper Shield formed between 8 and 9 million years ago. Some of the youngest igneous units on the island are trachyte intrusions from 7 to 8 million years ago. In some cases, more felsic trachyte actually formed flows, now preserved as Turk's Cap, Little Top and Great Stone Top. Trachyte masses are especially common on the southwest of the island.
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Map of the Seychelles The geology of Seychelles is an example of a felsic granite microcontinent that broke off from the supercontinent Gondwana within the past 145 million years and become isolated in the Indian Ocean. The islands are primarily granite rock, with some sequences of sedimentary rocks formed during rift basin periods or times when the islands were submerged in shallow water.
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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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Melts caused by subduction have generated the volcanoes of the Andean Volcanic Belt including the APVC. The volcanic province is located between 21° S–24° S latitude. The APVC spans the countries of Argentina, Bolivia and Chile. In the Miocene–Pliocene (10-1 mya), calderas erupted felsic ignimbrites in four distinct pulses separated by periods of low levels of activity.
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There are two felsic volcanic complexes in the Skellefte district south of the greenstone belts, spanning into the Arvidajavar district. These rocks deposited below water and were later affected by low-grade metamorphism. South of the Skellefte district in north-central Sweden, in the Bothnian Basin, metagrayacke interlayers with metavolcanic rocks and metamorphosed under high pressure to paragneiss and migmatite.
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At the same time, crustal extension took place because the mountain range was isostatically unstable (this is called orogenic collapse). Due to extension, basins formed along the axis of the mountain range and felsic volcanism occurred. This was the first phase of rifting between Europe and Africa. Due to the rising sealevel in the Triassic period, the eastern margin of Pangaea was flooded.
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Rhyolite and other felsic rocks can also be found in these zones. Continued extension with volcanic activity forms transitional crust, welding ruptured continent to nascent ocean floor. Volcanic beds cover the transition from thinned continental crust to oceanic crust. Also occurring during this phase is the formation of high velocity seismic zones under the thinned continental crust and the transition crust.
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Average density of sial is 2.7 gm/cc. Geologists often refer to the rocks in this layer as felsic, because they contain high levels of feldspar, an aluminium silicate mineral series. However, the sial "actually has quite a diversity of rock types, including large amounts of basaltic rocks." The name 'sial' was taken from the first two letters of silica and of alumina.
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These are overlain by lower Paleozoic (Cambrian to Devonian) (meta-)sediments. The whole sequence was deformed, metamorphosed and intruded by felsic magmas during the Hercynian orogeny. The massif is cut in three by two major late Hercynian southeast-northwest striking shear zones (the North and South Armorican Shear Zones). The divisions are simply called the North, Central and South Armorican Zones.
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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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It is interpreted as part of the Deccan Traps, which arose from the "tumultuous outpour of lava beyond 106 cubic km in volume. Eruption is deduced to have occurred 69-65 Ma age. These basaltic rocks said to be one of the largest continental flood basaltic provinces in the world." Studies carried by geologists have indicated eleven basic flows superposed by felsic volcanics.
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Ulleung Island is a volcanic island in the Sea of Japan, whose composition is more felsic than Jeju-do. The volcanic islands tend to be younger, the more westward. Because the mountainous region is mostly on the eastern part of the peninsula, the main rivers tend to flow westwards. Two exceptions are the southward-flowing Nakdong River (Nakdonggang) and Seomjin River (Seomjingang).
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Volcanic islands are common in the Izu segment, including O-shima, Hachijojima, and Miyakejima. The Izu segment farther south also contains several submarine felsic calderas. The Izu arc segment is also punctuated by inter-arc rifts. The Bonin segment to the south of the Sofugan Tectonic Line contains mostly submarine volcanoes and also some that rise slightly above sealevel, such as Nishino-shima.
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The Sierra de Gredos comprises mainly granite, which is a common type of intrusive, felsic, igneous rock which is granular and phaneritic in texture. This rock consists mainly of quartz, mica, and feldspar. In some Gredos rocks the feldspar crystals are especially large, attaining a size of several centimeters in some cases. There is also some granodiorite and outcrops of metamorphic rocks.
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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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These rocks are often thrusted over the alluvial rocks of the sub-Himalaya. The Lesser Himalaya also contains granites and felsic volcanic rocks. The Central Himalayan Domain contains rocks from the Tethys Ocean and is also intruded by Miocene granites, related to the formation of the Himalaya. The Indus Suture Zone is the suture zone with the Lhasa terrane to the North.
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In historical times, Lanín has been the least active of these volcanoes. Apart from Quetrupillán and Villarrica, there are a number of old eroded remains of stratovolcanoes in the alignment. The volcano itself rests on a basement of gneisses, felsic plutons, and volcaniclastic sequences. The basement rocks constitute a tectonically elevated block limited in the west by the north- south Reigolil-Pirihueico Fault.
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Titanite occurs as a common accessory mineral in intermediate and felsic igneous rocks and associated pegmatites. It also occurs in metamorphic rocks such as gneiss and schists and skarns. Source localities include: Pakistan; Italy; Russia; China; Brazil; Tujetsch, St. Gothard, Switzerland; Madagascar; Tyrol, Austria; Renfrew County, Ontario, Canada; Sanford, Maine, Gouverneur, Diana, Rossie, Fine, Pitcairn, Brewster, New York and California in the US.
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The Flood Range consists of a linear volcanic chain of peaks in which there have been systematic migrations of felsic activity. This activity has moved 90 km from east to west between 9 million and 2.5 million years ago, and 154 km northward from the south end of the Ames Range toward Shepard Island between 12.7 and 0.6 million years ago.
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The temperature of the magma chamber has been estimated to be about , with heating of over occurring before some eruptions according to thermometry calculation. Volcanic activity was most likely triggered by the injection of basaltic magma into the felsic magma chamber before the actual eruption. The amphiboles in the rocks formed at depths of . The magma output of Ciomadul is about .
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Ulleung Island is a volcanic island in the Sea of Japan, the composition of which is more felsic than Jeju-do. The volcanic islands tend to be younger, the more westward. Because the mountainous region is mostly on the eastern part of the peninsula, the main rivers tend to flow westwards. Two exceptions are the southward-flowing Nakdong River and Seomjin River.
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Just to the northeast is Itcha Mountain, the second highest peak with an elevation of . These peaks are situated on top of the shield, which has a topographic prominence of about . The Itcha Range has a broad, gently sloping structure typical of shield volcanoes. It is mainly composed of thick felsic lava flows that were erupted from a central vent.
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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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South of the Fraser River at Wahleach Lake is the Mount Barr Plutonic Complex. Named after Mount Barr in the Skagit Range of the Cascade Mountains, this plutonic complex ranges in age from 21 to 16 million years old. It consists of at least four plutons. The main pluton, comprising 80% of the complex, comprises felsic and intermediate intrusive rocks ranging from quartz diorite to quartz monzonite.
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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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Shield volcanoes undergo at least two stages of volcanic activity. The initial shield stage is the most productive volcanically and features repeated eruptions of large volumes of predominately fluid peralkaline felsic magmas that become progressively more evolved. During this stage, a small summit caldera may form, as is the case for the Ilgachuz Range. After the shield stage has been completed, the post-shield stage succeeds.
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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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In older rocks from the lower crust intrusions are found that formed during or just after the Hercynian orogeny. These intrusions are older than the Alps and have nothing to do with their formation. Radiometric age determination yields ages around 320 Ma. Slightly younger felsic intrusions formed by Permian and Triassic extension can also be found. Intrusions from the formation of the Alps themselves are relatively rare.
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In the Dial Range Trough the middle Cambrian saw the deposition of the Cateena Group of conglomerate (of purple mudstone pebbles), sandstone with feldspar, mudstone and greywacke and some felsic volcanics. The age is Florian to Undillan. This was followed by the Radfords Creek Group which has a base of a conglomerate of chert and basalt fragments. The age is Boomerangian to Late Mindyallan.
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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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The Quetico gneiss belt extends some across Ontario and parts of Minnesota. The dominant rocks within the belt are schists and gneisses produced by intense metamorphism of greywackes and minor amounts of other sedimentary rocks. The sediments, alkalic plutons and felsic plutons are aged from 2,690 to 2,680 million years. The metamorphism is relatively low-grade on the margins and high-grade in the center.
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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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Rock chemistry and isotope analysis suggests that at first the Farallon Negro system was not underpinned by a magma chamber. Starting in 8.5 mya then a heterogeneous magma chamber was probably established, with an increasing content of felsic rocks at its roof. A minimum volume of is required to explain the formation of the Alumbrera deposit. This magma chamber probably had a heterogeneous composition.
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The nucleation of bubbles causes a rapid expansion and cooling of the surrounding melt, producing glassy shards that may erupt explosively as tephra (also called pyroclastics). Fine-grained tephra is commonly referred to as volcanic ash. Whether a volcano erupts explosively or effusively as fluid lava depends on the composition of the melt. Felsic magmas of andesitic and rhyolitic composition tend to erupt explosively.
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Heavy, soft and fragile, astrophyllite typically forms as bladed, radiating stellate aggregates. It is this crystal habit that gives astrophyllite its name, from the Greek words astron meaning "star" and phyllon meaning "leaf". Its great submetallic gleam and darkness contrast sharply with the light (felsic) matrix the mineral is regularly found within. Astrophyllite is usually opaque to translucent, but may be transparent in thin specimens.
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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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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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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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Dacitic lava flows or tuffs overlie these metamorphosed volcanic rocks along with intermediate volcanic breccias, and are overlain by rhyolite lava flows and tuffs. Acidic lava flow units range in thickness from to and are common in the Vermilion Lake and Link Lake areas. The felsic tuffs are normally altered and sheared. The most recent intrusive activity in the TGB was the formation of a rhyolite porphyry dike million years ago.
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Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite. Typically, the pure potassium endmember of orthoclase forms a solid solution with albite, the sodium endmember (NaAlSi3O8), of plagioclase. While slowly cooling within the earth, sodium-rich albite lamellae form by exsolution, enriching the remaining orthoclase with potassium. The resulting intergrowth of the two feldspars is called perthite.
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Adularia with pyrite incrustations The higher-temperature polymorph of KAlSi3O8 is sanidine. Sanidine is common in rapidly cooled volcanic rocks such as obsidian and felsic pyroclastic rocks, and is notably found in trachytes of the Drachenfels, Germany. The lower-temperature polymorph of KAlSi3O8 is microcline. Adularia is a low temperature form of either microcline or orthoclase originally reported from the low temperature hydrothermal deposits in the Adula Alps of Switzerland.
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The Precambrian basement in Queensland is west of the Tasman Line. It includes elements such as the Mount Isa Orogen and the Georgetown Inlier. The Mount Isa Orogen started with sediments, volcanics and intrusive rocks, and was deformed and metamorphosed during the Barramundi Orogeny 1870 Mya. Sedimentary layers formed on top, firstly felsic volcanic rocks from 1870 to 1850 Mya. Shallow water sediments formed from 1790 to 1705 Mya.
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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 formation is made up of volcaniclastic rocks, and non- volcaniclastic rocks such as andesite, basalt, basaltic andesites and some lesser amounts of dacite. The non-volcaniclastic rocks correspond variously to lava flows with autobrecciated parts, lava domes, cryptodomes and pillow lavas. The volcaniclastic rocks of the formation include hyaloclastite breccias, peperites and felsic ignimbrites. This last rock type forms at some locations the lowermost parts of the formation.
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Because of Level Mountain's great extent it can be seen from outer space. This, coupled with elevation and snow, helps define the geology of the region. Level Mountain lies on the Nahlin Plateau, a subdivision of the larger Stikine Plateau that is dominated by the volcano. The basement of the shield consists largely of felsic igneous rocks comprising northern Stikinia, but sedimentary rocks are also present below the lava plateau escarpment.
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Guyana occurs within the northern part of the Guiana Shield. The Guiana Shield forms the northern part of the Amazonian Craton, the core of the South American continent. Most of the geology of northern Guyana consists of Palaeoproterozoic Orosirian greenstone belts (Barama and Mazaruni Supergroups) intruded by granites. These are overlain unconformably by the Statherian Burro-Burro Group, which consist of the Muruwa Formation sandstones and Iwokrama Formation felsic volcanics.
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Monzogranites are biotite granite rocks that are considered to be the final fractionation product of magma. Monzogranites are characteristically felsic (SiO2 > 73%, and FeO + MgO + TiO2 < 2.4), weakly peraluminous (Al2O3/ (CaO + Na2O + K2O) = 0.98–1.11), and contain ilmenite, sphene, apatite and zircon as accessory minerals. Although the compositional range of the monzogranites is small, it defines a differentiation trend that is essentially controlled by biotite and plagioclase fractionation. (Fagiono, 2002).
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Quarry for the Salt Lake Temple with boulders and detached masses being worked by stone cutters Quartz monzonite or adamellite is an intrusive, felsic, igneous rock that has an approximately equal proportion of orthoclase and plagioclase feldspars. It is typically a light colored phaneritic (coarse- grained) to porphyritic granitic rock. The plagioclase is typically intermediate to sodic in composition, andesine to oligoclase. Quartz is present in significant amounts.
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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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An Sgùrr, Eigg, Scotland Pitchstone is a dull black glassy volcanic rock formed when felsic lava or magma cools quickly. It is similar to obsidian but is defined by the International Union of Geological Sciences as having a higher water content. It is a volcanic glass; however, unlike a glass, pitchstone has an irregular hackly fracture not a conchoidal fracture. That is due to its coarser (than obsidian) crystal structure.
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Approximately 17 peaks can be accounted for as being over in height. Due to the presence of a variety of flora and fauna, the Sahand mountains are known as the bride of mountains in Iran. The absolute dating of Sahand rocks indicates that this volcano has been sporadically active from 12 million years ago up to almost 0.14 million years ago. Sahand is made chiefly of dacite and associated felsic rocks.
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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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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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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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Tridymite is a high-temperature polymorph of silica and usually occurs as minute tabular white or colorless pseudo-hexagonal crystals, or scales, in cavities in felsic volcanic rocks. Its chemical formula is SiO2. Tridymite was first described in 1868 and the type location is in Hidalgo, Mexico. The name is from the Greek tridymos for triplet as tridymite commonly occurs as twinned crystal trillings (compound crystals comprising three twinned crystal components).
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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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As the crystals themselves possess perfect cleavage, they are typically left in situ, the entire aggregate often cut into slabs and polished. Owing to its limited availability and high cost, astrophyllite is seldom seen in an ornamental capacity. It is sometimes used in jewellery where it is fashioned into cabochons. Found in cavities and fissures in unusual felsic igneous rocks, astrophyllite is associated with feldspar, mica, titanite, zircon, nepheline, and aegirine.
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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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Most ignimbrites are silicic, with generally over 65% SiO2. The chemistry of the ignimbrites, like all felsic rocks, and the resultant mineralogy of phenocryst populations within them, is related mostly to the varying contents of sodium, potassium, calcium, the lesser amounts of iron and magnesium. Some rare ignimbrites are andesitic, and may even be formed from volatile saturated basalt, where the ignimbrite would have the geochemistry of a normal basalt.
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These faster moving models have overcome major thermal and mechanical problems embedded in older theories as well as the granite problem and near surface felsic volcanism. As the flow of rising magma then changes from vertical back to horizontal, emplacement is initiated. This process is episodic and accommodated by both ongoing regional tectonics and emplacement-generated wall rock structures allowing the pluton to spread laterally and thicken vertically.
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The most famous one is continental growth model which is similar to the modern tectonic dynamics. Relatively low crystallisation temperature and some are enriched in heavy oxygen, contain inclusion similar to modern crustal processes and show evidence of silicate differentiation at ~4.5 Ga. Early terrestrial hydrosphere, early felsic crust in which granitoids were produced and later weathered under high water activity conditions and even the possible existence of plate boundary interactions.
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Their names derive from their formation, geographical location or distinctive features. Generally, porphyry-type mineral deposits form in hydrothermal fluid circulation systems developed around felsic to intermediate magma chambers and/or cooling plutons. However, they did not precipitate directly from the magma. While, a skarn deposit is an assemblage of ore and calc-silicate minerals, formed by metasomatic replacement of carbonate rocks in the contact aureole of a pluton.
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In a global scale, detrital zircon age abundance can be used as a tool to infer significant tectonic events in the past. In Earth's history, the abundance of magmatic age peaks during periods of supercontinent assembly. This is because supercontinent provides a major crustal envelop selectively preserve the felsic magmatic rocks, resulting from partial melts. Thus, many detrital zircons originate from these igneous provence, resulting similar age peak records.
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When hot pumice deposits on a cool surface, it is rapidly cooled, recrystallised and welded into quartz with flame-like ending tips. The eutaxiitc texture represents a hot vapour-phase emplacement of the fragmented volcanic materials on the Earth's surface. Flow bands are present in massive, uniform felsic lava flow units. When the viscous lava flow encounters a surface, friction drags the mobile lava and forms internal banding.
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Two stages of volcanic activity constructed the Itcha Range. The first stage, referred to as the felsic shield-building stage, occurred between 3.8 and 3.0 million years ago. Three phases comprise this stage; a pre-explosive phase, an explosive phase and a post-explosive phase. Analysis of the first trachyte magmas to erupt during the pre-explosive phase suggest they were relatively fluid as shown by their areal extent.
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The volcano is composed of alkali feldspar granitic rock of the Robertson River Igneous Suite. This includes felsic complex material such as biotite, hornblende-biotite, magnetite, and alkali granitic rock including rhyolite on the eastern slopes of Battle Mountain and the adjacent (and geologically related) Little Battle Mountain (elevation 937 feet). Theorized original appearance of Battle Mountain at 704 million years ago by Woolman (2016). Elevation shown in meters.
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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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Reassessment of the geophysical signature at Maggie Hays indicates that the hangingwall banded iron formation is as conductive as the massive sulfides, and that on this basis, as well as the steep orientation of the massive nickel sulfides, Maggie Hays is essentially blind to discovery. The Emily Ann orebody is situated approximately 1200 m north of the Maggie Hays orebody and was drilled first in 1998 after a prolonged and saturated effort to electromagnetically prospect the entire prospective belt. The Emily Ann orebody was unequivocally discovered by geophysical surveying, the result of a flatter orientation of the orebody, the fact it is hosted within conductively dead felsic gneiss, and the depth of the upper parts of the orebody reaching to within 200m of the surface. The Emily Ann discovery was a technical triumph, because it is a mechanically displaced recumbent fold of sheared massive sulfide hosted several hundred metres off the original ultramafic-felsic contact in a position not generally expected to host nickel sulfides.
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The northern shore of the Petitcodiac River, including the Anagance and North rivers, is primarily made up of shale with volcanic rocks, mixed igneous rocks, and felsic pebble conglomerates. The southern shore, including the Little and Pollett rivers, is composed of Precambrian or Lower-Palaeozoic sedimentary, igneous, and volcanic rocks, and limestone. Both shores include red to grey Mississippian sandstone. Red beds, or red-tinted sedimentary rocks, have a higher occurrence around Port Elgin.
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The Gawler Craton formed more than three million years ago in the process of felsic magmatism, the movement of silicate minerals and magma. The area continued to experience these processes, as well as sedimentation, until one and a half million years ago. The Gawler Craton is resource rich, having an abundance of meta-sedimentary rock. Due to its extent and age, the Gawler Craton is also a source for many precious metals and gems.
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All dike types were placed in the Earth's crust during the formation of the TGB. At least some of these dikes may have been subvolcanic feeders that produced known calc-alkalic felsic volcanic events in the belt. Many pyroxenite dikes less than wide intrude every geologic formation in the township. A pyroxenite dike east of Highway 11 extends roughly to the north-northwest while two others, north of Arsenic Lake, extend to the east.
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This type of basalt contains tabular feldspar phenocrysts that range up to in cross section. Both pillowed and massive lava flows have been known to contain coarse feldspar. Coarse feldspar-bearing, iron tholeiitic basalts are more common east of Highway 11. A number of volcanic rocks comprise the Link Lake Formation, such as feldspar-phyric, calc-alkaline basalt and andesite lava flows and less abundant quartz and quartz-feldspar- phyric felsic lava flows.
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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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Granitoids have crystallized from felsic magmas that have compositions at or near a eutectic point (or a temperature minimum on a cotectic curve). Magmas are composed of melts and minerals in variable abundances. Traditionally, magmatic minerals are crystallized from the melts that have completely separated from their parental rocks and thus are highly evolved because of igneous differentiation. If a granite has a slowly cooling process, it has the potential to form larger crystals.
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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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Between the Beemerville alkaline complex and the Cortlandt igneous complex, this magmatic belt consists of a linear, almost east-west trending, zone of lamprophyre and felsic dikes.Ratcliffe, NM (1981) Cortlandt- Beemerville magmatic belt: A probable late Taconian alkalic cross trend in the central Appalachians. Geology 9(7):329-335. The currently accepted age for the emplacement Beemerville Alkaline Complex is 420 ± 6 Ma. This age is derived by the fission track dating of titanite.
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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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It belongs to the same rock class, felsic, as granite but is much less common. The Amargosa River, which flows through nearby Beatty, gets its name from the Spanish word for "bitter", amargo. In its course, the river takes up large amounts of salts, which give it a bitter taste. "Bullfrog" was the name Frank "Shorty" Harris and Ernest "Ed" Cross, the prospectors who started the Bullfrog gold rush, gave to their mine.
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A projection of the unit cell is shown by the black rectangle. Iron rich olivine is a relatively common constituent of acidic and alkaline igneous rocks such as volcanic obsidians, rhyolites, trachytes and phonolites and plutonic quartz syenites where it is associated with amphiboles. Its main occurrence is in ultramafic volcanic and plutonic rocks and less commonly in felsic plutonic rocks and rarely in granite pegmatite. It also occurs in lithophysae in obsidian.
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The youngest magmatism of the youngest magmatic series is 1,870 million-year- old felsic and carbonatitic volcanics. These igneous rocks of the Labrador Trough cover an area of . To the northwest at the northern tip of Quebec near Hudson Strait, the Cape Smith Belt includes the 2,040 to 1,970 million-year- old Povungnituk volcano-sedimentary group and the 1,880 million-year-old Chukotat Group. The thick Chukotat Group is made of picritic and tholeiitic basalts.
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Syenogranite is a fine to coarse grained intrusive igneous rock of the same general composition as granite. They are characteristically felsic. The feldspar component of syenogranite is predominantly alkaline in character (usually orthoclase). For example, the syenogranite in the Salmon Mountains in Idaho is pink to tan and composed of 45–55% alkali feldspar, 15–20% plagioclase, 15–20% quartz, 5–8% biotite, 3–5% hornblende, and accessory magnetite (Evans and Green, 2003).
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Eclogites in granulite terranes are known from the Musgrave Block of central Australia where a continental collision took place at 550-530 Ma, resulting in burial of rocks to greater than 45 km (15 kilobars) and rapid (in less than 10 million years) exhumation via thrust faults prevented significant melting. Felsic rocks in these terranes contain sillimanite, kyanite, coesite, orthoclase and pyroxene, and are rare, peculiar rocks formed by an unusual tectonic event.
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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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On the rock surface in the case hardening of alkaline felsic rocks, the weathering selectively affects certain minerals. Nepheline is very sensitive to weathering and is altered to natrolita and cancrinite. On the outcropping surface of a nepheline syenite, phonolite or nepheline syenite gneiss, the minerals formed by nepheline alteration appear white in colour on the dark- coloured weathered background. After the nepheline alteration products are leached, small holes are formed on the rock.
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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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Lava domes and coulées are associated with felsic lava flows ranging from dacite to rhyolite. The very viscous nature of these lava cause them to not flow far from the vent, causing the lava to form a lava dome at the vent. When a dome forms on an inclined surface it can flow in short thick flows called coulées (dome flows). These flows often travel only a few kilometers from the vent.
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Three levels were created, two of which had of lateral work. Reserves have been variously estimated at 31,000 tons averaging of gold per ton, 45,700 tons averaging of gold per ton over , or 9,000 tons averaging of gold per ton over . A main and subsidiary quartz- rich zone occur in a ruptured intrusion composed of diorite, which intrudes felsic volcanic rocks in a northwesterly direction with the strike of the Net Lake-Vermilion Lake Deformation Zone.
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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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However, in minerals with low calcium content (under 1/50th of the potassium content), this dating method becomes useful. Examples of such minerals include lepidolite, potassium-feldspar, and late-formed muscovite or biotite from pegmatites (preferably of older than 60 Ma). This method is also useful for zircon-poor, felsic-to-intermediate igneous rocks, various metamorphic rocks, and evaporite minerals (i.e. sylvite).Ahrens., L.H. The feasibility of a calcium method for the determination of geological age. Geochim. Cosmochim.
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Jeju Island, situated off the southern coast, is a large volcanic island whose main mountain Mount Halla or Hallasan (1950 m) is the highest in South Korea. Ulleung Island is a volcanic island in the Sea of Japan, the composition of which is more felsic than Jeju-do. The volcanic islands tend to be younger, the more westward. Because the mountainous region is mostly on the eastern part of the peninsula, the main rivers tend to flow westwards.
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The Svecokarelian Orogeny between 1.95 and 1.85 billion years ago deposited the metavolcanic and metasedimentary Svecofennian-Kalevian rocks, along with calc- alkaline granitoid intrusions. Felsic metavolcanic rocks from 1.9-1.88 billion years ago are the uppermost sequence in the Kiruna area. The region also has some meta-greywacke and mica schist. Dating of rocks in the Finnish part of the Fennoscandian Shield suggests that the rocks there are somewhat older, forming starting two billion years ago.
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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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The usefulness of Sm–Nd dating stems from the fact that these two elements are rare earth elements and are thus, theoretically, not particularly susceptible to partitioning during sedimentation and diagenesis. Fractional crystallisation of felsic minerals changes the Sm/Nd ratio of the resultant materials. This, in turn, influences the rate at which the 143Nd/144Nd ratio increases due to production of radiogenic 143Nd. In many cases, Sm–Nd and Rb–Sr isotope data are used together.
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The geology of South Georgia and the South Sandwich Islands is part of the largely submerged Scotia Ridge. The island of South Georgia is unusual among oceanic islands for having pre-Cretaceous sedimentary rocks underlying much of the island and a significant portion of felsic igneous rocks. Two-thirds of the island consists of intensely folded flysch, capped with Aptian age fossils, tuff and greywacke in the Cumberland Bay Series. The series includes slate, phyllite, conglomerate, siltstone and sandstone.
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The Quinchía Project, covering an area of , encompasses multiple porphyry gold target centers that have been early stage drill tested in 2006. Three historic Miocene intrusive centers have been identified, spaced out over a north to south strike, and are at elevations between . These intrusive centers are composed of dykes and stocks emplaced in intermediate to felsic volcanic rocks of the Miocene Combia Formation and in Cretaceous basalts. All target centers host gold and copper mineralization.
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Another model of Archean SCLM formation suggests that the SCLM formed in a subduction environment in which new Archean crust was created through slab melting. If the primitive mantle is the starting composition for this SCLM formation event, subducting slab would be composed of TTG crust, then the removal of basaltic melt and the enrichment of the mantle wedge with felsic melts could explain the formation of the depleted Archean subcontinental lithosphere. For more information, see Archean subduction.
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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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However, considerable displacement of the dikes at this location is unknown. The most recent tectonic activity of the Big Dan Shear Zone displaced a Proterozoic dike composed of diabase, which intersects the zone. A similar abundance of felsic dikes are adjacent to Arsenic Lake just west of Highway 11, indicating that similar tectonism also occurred along that structural zone. Therefore, these north-trending shear zones may have been tectonically active for at least a billion years.
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In the Mesozoic, rifting in the Triassic began to break apart the supercontinent Pangea which had assembled during the Alleghanian orogeny. Thinning of the crust produced diabase dikes in the early Jurassic 200 million years ago throughout the Piedmont, as well as felsic dikes and diabase sills in the Deep River Basin. Seismic data indicates that large basalt flows found offshore extend onshore, reaching Charleston, South Carolina. Few Cretaceous and Jurassic rocks are rare on the continental margin.
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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 predominant bedrock at Beanland Mine is basalt and andesite. A series of sheared, carbonatized rhyolite lava flows are exposed north of Beanland. These form part of the Older Volcanic Complex, a unit of the Temagami Greenstone Belt made of mostly felsic volcanic rocks.
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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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Igneous rocks can become foliated by alignment of cumulate crystals during convection in large magma chambers, especially ultramafic intrusions, and typically plagioclase laths. Granite may form foliation due to frictional drag on viscous magma by the wall rocks. Lavas may preserve a flow foliation, or even compressed eutaxitic texture, typically in highly viscous felsic agglomerate, welded tuff and pyroclastic surge deposits. Metamorphic differentiation, typical of gneisses, is caused by chemical and compositional banding within the metamorphic rock mass.
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The Sleaford orogeny was an event in the assembly of the Gawler Craton, which now underlies the Eyre Peninsula in South Australia. Between 2.46 and 2.41 billion years ago in the Proterozoic, the Sleaford and Mulgathing complexes emplaced among the older 3.15 billion year old Archean Cooyerdoo Granite 2.82 billion year old Coolanie Gneiss with sedimentary, felsic and ultramafic igneous rocks. The overlapping Sleaford orogeny caused deformation and greenschist and granulite-grade metamorphism on the sequence of metamorphic facies.
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When the rare earth element-enriched felsic magma cools down to become rock, intense weathering of the rock further concentrates the rare earth element deposit. Therefore, the property of magma and the weathering intensity is the key to concentrate the rare earth element deposits. In South China, 75% of these deposits were derived from granitic and volcanic rocks during the Jurassic to the early Cretaceous. Therefore, the Yanshanian Movement represents one of the vital geological events in South China.
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Other than the plutons, plentiful Eoarchean detrital zircons were reported from the metamorphosed sedimentary rocks in eastern Hebei and few in Anshan. Biotite schist, fuchsite quartzite and paragneiss recorded an isotopic age of 3.88–3.55 billion years. This further reinforces the existence of a Hadean- Eoarchean crust, which later became the sedimentary protolith of the metamorphosed sedimentary rocks. In Xinyang, at the southwestern edge of the Eastern Block, 3.6 billion-year-old zircons from felsic granulite xenoliths were found.
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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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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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Mount Cayley viewed from southeast showing light coloured breccia cut by a central spine of dacite which forms the summit ridge. The early Mount Cayley stage was characterized by the eruption of felsic lava flows and pyroclastic rocks onto a crystalline basement. Initial volcanism formed a southwesterly-dipping prism of dacite flows and tephra cut by several dikes and sills. These rocks have been hydrothermally altered to varying degrees and are light yellow or red in colour.
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The warm water Saraburi Group in the east has numerous fossils, while the Ratburi Group in the west does not. In peninsular Thailand, sandstone is predominant interfingered with Ratburi Group limestones. Along the western edge of the Khorat Plateau, a limestone dominated shelf sequence abuts turbidites and pyroclastic flow deposits. A magmatic arc around a west-dipping subduction zone produced intermediate and felsic volcanic rocks in the north around Lampang to the east of Chiang Mai.
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Skarn formation, as illustrated in the figure on the right, can be explained in three stages: # Intrusion of a felsic to intermediate magma body rich in volatiles. Contact metamorphism and minor metasomatism, skarn formation, occurs in favorable locations. # Continued crystallization of the magma and widespread release of volatiles as a hydrothermal fluid which causes widespread skarn formation and localized brecciation. # Characterized by decreasing temperatures and hydrothermal activity, during which sulfide deposition occurs in veins and retrograde alteration is common.
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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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Modified from Moyen & Martin, 2012. Geochemical similarity shared between TTGs and adakites was long noted by researchers. Adakites are one type of modern arc lavas, which differ from common arc lavas (mostly granitoids) in their felsic and sodic nature with high LREE but low HREE content. Their production is interpreted to be the partial melting of young and hot subducting oceanic slabs with minor interaction with surrounding mantle wedges, rather than mantle wedge melts like other arc-granitoids.
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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 older GMS-like felsic volcanic rocks formed with similar age of TTG has two implications: #GMS may have intruded the crust and GMS-like volcanics at a very shallow depth. Later, intense erosion rips up all GMS suites and deposited at a proximal distance. If this is true, then GMS and TTG intruded the crust together at the same time. No solid evidence is present yet but the irregular geochemical fingerprints may link both to TTG or GMS.
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The felsic shield-building stage ended with the post-explosive phase. This phase of activity created small volcanic plugs, lava flows, minor pyroclastic flows, channelized debris flows and a few glassy dikes at the summit of the shield volcano. These consist of alkali-feldspar porphyritic quartz-trachyte and trachyte. Alkali- feldspar quartz-trachyte plugs formed in rhyolites and trachytes of the pre- explosive phase, as well as pyroclastic deposits and feldspar trachyte lava flows of the explosive phase.
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These metasedimentary rocks were originally composed of particles of quartz, clay, and volcanic rock fragments that have become metamorphosed into various schists. The Vishnu Schist exhibits relict graded bedding and structures indicative of turbidite deposits that accumulated in oceanic trenches and other relatively deep-marine settings. The Brahma Schist has been dated to about 1.75 billion years ago. The felsic metavolcanic rocks that comprise the Rama Schist have yielded an age of 1.742 billion years ago.
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The Lynn Volcanic Complex is a suite of Proterozoic felsic volcanic rocks, situated in a block north of the Boston Basin. It includes rhyolite, rhyodacite, welded ash flows, tuff and some andesite and basalt (although some of these may actually be part of the Middlesex Fells Volcanic Complex). Unlike the neighboring Mattapan Volcanic Complex, the Lynn complex lacks volcanic breccia and has a greater variety of texture and composition in its rhyolitic rocks. It lies unconformably on top of the Dedham Granite.
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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 main exposure lies immediately south of the Kanichee Mine Road, which branches off Highway 11. Minor gold and copper values constitute this zone. This sulfide-bearing unit is located within felsic volcanic rocks of the Older Volcanic Complex and is capped by large, dark green, iron-rich tholeiitic basalts of the Arsenic Lake Formation. It has been interpreted that the sulfide zone represents a volcanogenic massive sulfide ore deposit based on the structure of the sulfide zone and the associated rock types.
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Geologists assume that greenstone belts were formed by many geological processes, such as tectonism, magmatism, metamorphism and sedimentation. They are important economically for large metal deposits, and for the insight they provide into crustal evolution and the tectonics of the early Earth. The TGB is wide and long. It contains the southernmost remnants of Archean intrusive and supracrustal rocks in Eastern Ontario, as well as some of the most ancient felsic magmatic events in this section of the Superior craton.
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The thickest portion of this lava flow or dome is located at the western end of Link Lake, where it is likely associated with a volcanic vent. The bulk of felsic rock in the Link Lake Formation occurs as subaqueous pyroclastic flow deposits. Subearial pyroclastics are normally quartz-phyric and range up to in crosssection. Dark green subearial pyroclastics composed of chlorite and sericite are uncommon and have sustained preferential compression in response to shear throughout the Link Lake Deformation Zone.
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Lakes, volcanic complexes and deformation zones of Strathy Township. Also shown are portions of the massive Chambers-Strathy Batholith Many north-trending shear zones intersect iron-rich tholeiitic basalts of the Arsenic Lake Formation. These zones range in width from less than up to , and might maintain a larger area of weakness that was tectonically active over the past billion years. Evidence for early tectonism, likely related to volcanic activity, include the greater density of felsic dikes concentrated immediately around these zones.
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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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Arvidsjaur porphyry () is a group of igneous rocks of intermediate to felsic composition found near Arvidsjaur in northern Sweden. The Arvidsjaur Porphyry formed 1,870 to 1,880 million years ago during the Paleoproterozoic Era. Most of the porphyry have well-preserved primary structures and textures which have allowed to interpret much of Arvidsjaur porphyry to be ignimbrites. While much of the porphyryry have rhyolite compositions some parts that are interpreted as lava flows are made up of andesite with plagioclase phenocrysts.
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In modern usage, the term acid rock, although sometimes used as a synonym, normally now refers specifically to a high-silica-content (greater than 63% SiO2 by weight) volcanic rock, such as rhyolite. Older, broader usage is now considered archaic. That usage, with the contrasting term "basic rock", was based on an incorrect idea, dating from the 19th century, that "silicic acid" was the chief form of silicon occurring in rocks. The term "felsic" combines the words "feldspar" and "silica".
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Many researchers proposed that the Western Block of the North China Craton was assembled in the Paleoproterozoic (2.5-1.6 billion years ago), creating a linear structure composed ofkhondalite that cuts across the Western Block. The khondalite belt stretches from Helanshan in the west to Jining Complex in the east. Pelitic granulites, quartzite, felsic paragneiss and marble, which are the members of the "khondalite series", are exposed along this belt. The khondalite series is metamorphosed from sedimentary protoliths formed under stable continental margin condition.
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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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Rock veneers commonly arise from the weathering of resistant rocks of quartzite, felsic granites, coarse granites, and dense basalts. As these larger rocks are deposited on a surface, smaller sands either are removed by wind or water erosion, or settle and form a fine-grained layer beneath the larger veneer rocks. The larger clasts then rearrange and settle to form the rock veneer.Lenart, M.T., Osterkamp, W.R., and Toy, T.J., "Development of partial rock veneers by root throw in a subalpine setting".
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The "Copper Coast" has evolved over the last 460 million years after it was formed by volcanic activity in the Ordovician period. The oldest felsic volcanic rocks have intrusive elements and are interspersed with shales. Sedimentary rocks from 370-360 Mya can be seen as reddish-brown conglomerates, sandstones, siltstones and shales. After a wide gap in geological time, the next exposed sequences are from the Quaternary period, and consist of unconsolidated tills, boulder clays and deposits of sand and gravel.
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The Deseado Massif (Spanish: Macizo del Deseado) is a massif in southern Patagonia located in the Argentine province of Santa Cruz. On surface the massif is made up of Middle to Late Jurassic-aged felsic volcanic rocks. Analysis of mantle xenoliths reveals that the lithospheric mantle of the Deseado Massif is about 2100 to 1000 million years old. As such the Deseado Massif is one of the oldest regions of Patagonia as it existed in some form during the Paleo and Mesoproterozoic.
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New Zealand's soils are affected by bedrock, climate, vegetation and the time it has had to develop, In the central North Island the felsic volcanic rocks is deficient in elements (like cobalt) needed by plants. While the rare ultramafic rocks of the South Island are so rich in required elements it is used as fertilizer. The warmer climate of Northland weathers rock more quickly leading to deeper soils. In Fiordland and similar wet steep environments landslides reduce the time for soil formation.
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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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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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Rain containing elevated concentrations of SO2 kills vegetation, which then reduces the ability of the area's biomass to absorb CO2 from the air. It also creates a reducing environment in streams, lakes, and groundwater. [15] Because of its high reactivity with other molecules, increased sulfur concentrations in the atmosphere can lead to ozone depletion and start a positive warming feedback. Volcanoes with a felsic melt composition produce extremely explosive eruptions that can inject massive quantities of dust and aerosols high into the atmosphere.
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The oldest supracrustal rocks are the Sebakwian Group (3.5 Ga) exposed around Shurugwi and Mashava, and northwest of Gweru, within the central craton. This group consist of metavolcanic rocks, including komatiite and basalt, banded iron formation, and clastic metasedimentary rocks. The Sebakwian Group is succeeded by the Bulawayan Group, further differentiated by the Lower Greenstones (2.9 Ga) and Upper Greenstones (2.7 Ga). The Lower Greenstones include felsic volcanic and volcaniclastic rocks, komatiites, and komatiitic basalts with interbedded iron-formations and polymict clastic sediments.
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Since the impact, 7–8 km of rock has eroded away, leaving no visible depressions (compare, in contrast, Iso-Naakkima, Lumparn). Sparse gravity data shows a negative anomaly (an area of lower gravity) in the area of the impact structure. However, there are other negative gravity anomalies nearby which are not believed to be related to the impact event. In addition, there are less dense felsic rocks in the western shore of the lake, which can contribute to the gravity low.
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This was followed by the third and final Shovelnose stage about 300,000 to 200,000 years ago with the emplacement of parasitic lava domes and flows. Although one of the Shovelnose domes has been potassium-argon dated at 310,000 years old, this date may be in error from excess argon. The Shovelnose stage rocks could be much younger, perhaps less than 15,000 years old. Eruptions during the three stages produced volcanic rocks of felsic and intermediate compositions, including andesite, dacite and rhyodacite.
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336x336px Detrital zircon geochronology is the science of analyzing the age of zircons deposited within a specific sedimentary unit by examining their inherent radioisotopes, most commonly the uranium–lead ratio. The chemical name of zircon is zirconium silicate and its corresponding chemical formula is Zr SiO4. Zircon is a common accessory or 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.
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Intermediate or andesitic lavas are lower in aluminium and silica, and usually somewhat richer in magnesium and iron. Intermediate lavas form andesite domes and block lavas, and may occur on steep composite volcanoes, such as in the Andes. Poorer in aluminium and silica than felsic lavas, and also commonly hotter (in the range of ), they tend to be less viscous. Greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and also a greater tendency to form phenocrysts.
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Valles Caldera National Preserve, New Mexico, United States Lava domes are formed by the extrusion of viscous felsic magma. They can form prominent rounded protuberances, such as at Valles Caldera. As a volcano extrudes silicic lava, it can form an inflation dome, gradually building up a large, pillow-like structure which cracks, fissures, and may release cooled chunks of rock and rubble. The top and side margins of an inflating lava dome tend to be covered in fragments of rock, breccia and ash.
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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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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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Above this in south east Tasmania are more marine units that include Nassau Formation Berriedale Limestone, up to 60 m thick, siltstone and sandstone rich in fossils and dropstones (Malbina Formation, and Deep Bay Formation), and the upper part is dark grey siltstone rich in dropstones. The very top layers are coloured black, probably from an estuary (Risdon Sandstone and the Abels Bay Formation). Felsic volcanic ash is found near the top of the sequence of sediments. Fresh water deposits form the Upper Parmeener Super Group.
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Klein, Cornelis and Hurlbut, Cornelius S. (1986), Manual of Mineralogy, Wiley, p. 484 The mass of the rock consists of a fine-grained matrix of felsic materials, particularly quartz, sodium and potassium feldspar, and may be termed a quartz felsite or quartz porphyry if the quartz phenocrysts are present. This rock is typically of extrusive origin, formed by compaction of fine volcanic ash, and may be found in association with obsidian and rhyolite. In some cases, it is sufficiently fine-grained for use in making stone tools.
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The fossils in this group were discovered by Arthur Hugh Hickman in 1983 in Warrawoona, , a region on the Pilbara craton in the northern part of Pilbara province. Whether or not the fossils are authentic was disputed in the past, as abiotic processes could not be ruled out. Currently the fossils are thought to be of biological origin, however there is no conclusive evidence of fossilized organisms in the formation, and whether the lines in the rock are fossilized stromatolites. The rocks also include felsic volcanic rocks.
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The geology of this whole region is considered to be part of the Mazaruni Group. The Wenot zone occurs along an approximately east-west regional shear dividing tuffaceous meta-sediments in the south from andesitic and basaltic meta- volcanics in the north. Small elongate vertical felsic intrusions with quartz veinlets within 100m of the shear contact host most of the gold. Much of this zone is hidden under later palaeo-alluvial sediments, and has been saprolitised to depths of up to 50m below the surface.
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Labrador is part of the eastern Canadian Shield and intrusive igneous or metamorphic rocks are the most common, with sedimentary rocks in some areas. Four of the seven Canadian Shield provinces make up Labrador. Archean age rocks and east-west structural trends mark the Superior Province (a small area in the west near Quebec) which encompasses the Ashuanipi Complex granulite and granodiorite intruded by pyroxene-rich felsic plutons. The Nain Province runs along the northeast coast and also has Archean-age rocks, although a greater northward trend.
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The geology of Saint Pierre and Miquelon is part of the 680 to 550 million year old, late Proterozoic Avalon Zone, a part of the Canadian Appalachians. The oldest rocks are 615 million year old metasedimentary and metavolcanic rocks, intruded by diorite and trondhjemite in the Cap de Miquelon Group. The metamorphic rocks are descended from an earlier volcanic arc-marine platform, rather than more ancient basement rock from the Avalonia microcontinent. The St. Pierre Group formed 581 million years ago with felsic and pyroclastic flows.
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The closer to the center of the undersea volcanoes the composition of the rocks shifts towards more felsic rock types such as Rhyolite, Rhyodacite, and Dacite. The source of this phenomenon is interpreted as a result from indicate formation from partial melting or fractional crystallization. This type of volcanism is commonly observed in Phanerozoic volcanic massive sulfide systems, and is not commonly observed in modern back-arc basins. Examples of where bimodal volcanism can be observed are the Okinawa Trough and the Sumizu Rift.
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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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Obsidian is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) causes a high viscosity, which, upon rapid cooling, results in a natural glass forming from the lava.Petrology The Study of Igneous...Rocks, Loren A. Raymond, 1995, McGraw-Hill, p. 27 The inhibition of atomic diffusion through this highly viscous lava explains the lack of crystal growth.
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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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Hot springs are also present in Iskut River Hot Springs Provincial Park and Choquette Hot Springs Provincial Park in northwestern British Columbia. Xenoliths, rock fragments that become enveloped in a larger igneous rock, are widespread in the Northern Cordilleran Volcanic Province. Xenoliths that originated in the Earth's crust include rich metamorphic rocks and felsic intrusive rocks. Granulite xenoliths exist mainly at the Fort Selkirk Volcanic Field in central Yukon, Prindle Volcano in easternmost Alaska and at Castle Rock and the Iskut River in northern British Columbia.
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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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The sedimentary rocks have been faulted and intruded by numerous felsic intrusives. The old Freiberg mine was worked for gold and silver starting in 1865. Later the New Freiberg mine was worked with underground and open pit methods for silver, lead, zinc and copper from 1919 through 1948.Tingley, Joseph P., The Mineral Resources of the Timpahute Range 30x60 Minute Quadrangle, Nevada Bureau of Mines and Geology, Report 46, 1991, pp 6-10 The Upper Devonian Guilmette Formation outcrops in the southern portion of the range.
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Other Paleogene igneous rocks on Arran include extensive felsic and composite sills in the south of the island, and the central ring complex, an eroded caldera system surrounded by a near- continuous ring of granitic rocks. Sedimentary rocks dominate the southern half of the island, especially Old and New Red Sandstone. Some of these sandstones contain fulgurites – pitted marks that may have been created by Permian lightning strikes. Large aeolian sand dunes are preserved in Permian sandstones near Brodick, showing the presence of an ancient desert.
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Schematic illustration of regional denudation for felsic alkaline intrusive rock bodies of the State of Rio de Janeiro, Brazil: Cabo Frio Island and Itaúna Body. In geology, denudation involves the processes that cause the wearing away of the Earth's surface by moving water, by ice, by wind and by waves, leading to a reduction in elevation and in relief of landforms and of landscapes. Endogenous processes such as volcanoes, earthquakes, and plate tectonics uplift and expose continental crust to the exogenous processes of weathering, of erosion, and of mass wasting.
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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 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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The Coquihalla Complex also has a different igneous composition than Canadian Cascade Arc volcanoes that formed in the last two million years. Rhyolite tuffs are the primary igneous rocks comprising the Coquihalla Volcanic Complex, with small amounts of basalt or andesite present. This contrasts with modern Canadian Cascade volcanoes in that they are mainly composed of volcanic rocks in the basalt to andesite composition range, with few rocks of more felsic composition than dacite. Changes in magma composition have also occurred in the American portion of the Cascade Arc.
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At the headwaters of Salal Creek is a roughly circular composite stock known as the Salal Creek Pluton. It is estimated to be 8.0 million years old, indicating that it is one of the youngest felsic plutons exposed in the Pacific Ranges. Like other Pemberton Belt plutons, the Salal Creek Pluton is generally thought by geologists to be the root of a deeply eroded volcano. Episodic eruptions may have formed a large dome, but rapid erosion to a depth of about has removed the overlying volcanic structure, exposing the wide Salal Creek Pluton.
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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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Yet Lorence G. Collins does not agree with the assumption of the K-feldspar being primary magmatic and the myrmekite being formed due to deformation-induced Na-Ca-metasomatism. His sampling beyond the shear zone revealed an undeformed, felsic biotite diorite whose primary plagioclase was being replaced from the inside out by K-feldspar due to K-metasomatism. The deformations were therefore more or less continuous and had not only affected the shear zone but also the older plutonic country rocks, thence bringing about a metasomatic change in mineralogy.
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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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Rhodochrosite on a Quartz "spear", from Climax mine The ore deposit is a porphyry type, similar to many large copper deposits, where many intersecting small veins of molybdenite form a stockwork in an altered quartz monzonite porphyry. Like other porphyry-type ore deposits, the ore is low- grade, much less than one percent molybdenum, but the ore bodies are very large. Beside molybdenum, the mine has also produced tin (from cassiterite), tungsten (from hübnerite), and pyrite as by-products. The rocks of the Climax Stock are alkaline felsic intrusives.
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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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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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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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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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Vertical movement may be thousands of meters and horizontal movements of many kilometers occur along some fault zones. Some time before , masses of magma intruded under and within the igneous and sedimentary rocks, heating and pressing the rocks to metamorphose them into hard greenish greenstones. They began with fissure eruptions of basalt, continued with intermediate and felsic rocks erupted from volcanic centers and ended with deposition of sediments from the erosion of the volcanic pile. The rising magma was extruded under a shallow ancient sea where it cooled to form pillowed greenstones.
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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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Earth Surface Process and Landforms, 24, 271-278 A similar phenomenon is observed in felsic alkaline rocks, such as nepheline syenite, alkaline syenite, phonolite, and trachyte, because of weathering vulnerability of nepheline and alkaline feldspar.Motoki, A., Soares, R., Lobato, M., Sichel, S.E., Aires, J.R. 2007. Feições intempéricas em rochas alcalinas félsicas de Nova Iguaçu, RJ. Revista Escola de Minas, 60-3, 451-548 The case hardening on trachytic clasts of volcanic breccia shows peculiar fabrics. The Mars scientific exploring machine Spirit has observed case hardening present of the rock surface present at Gusev meteorite Crater.
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The tailings of that operation can be seen today, and the area is part of the Petersville State Recreation Mining Area. A cluster of deposits is in the main part of the Yentna district, near the Dutch Hills. The productive deposits here have been placer gold deposits with byproduct platinum and locally abundant cassiterite. Gold-bearing lodes in the Yentna district, which have not been as well described, include small and locally very rich deposits associated with felsic dikes and apparently low-grade deposits in major shear and altered zones.
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The positive early results have created great interest for gold-finding efforts, and the Mount Meager massif has proven to be an ideal candidate. Granitic intrusions within the caldera complex include the McDougall Brook Microgranite and the somewhat younger Mount Pleasant Granite. Gold quartz breccias and veins cut the McDougall Brook Microgranite and its volcanic wall- rock, while molybdenum-bismuth-tungsten and later polymetallic mineralization are related to the multiphase Mount Pleasant Granite. The numerous felsic sections are associated with episodes of fractional crystallization in a high- level, zoned magma chamber.
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Sulfur is not strongly enriched during differentiation, in contrast to water, chlorine, and fluorine. The reason could be pre- or syn-eruptive degassing of a separate vapor phase, such as that postulated for the Pinatubo and Redoubt eruptions. The ultimate source for the excess volatile observed during the 1991 Pinatubo eruption is assumed to be sulfur-rich basaltic magmas underlying, and syn- eruptively intruded, into the overlying felsic magmas. The sulfur-rich trachytic and trachyandesitic magmas which underlay the rhyolitic magma at Changbaishan may have been a possible source for excess sulfur accumulation.
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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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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 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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Silicic magmas typically form blocky lava flows or steep-sided mounds, called lava domes, because their high viscosity does not allow it to flow like that of basaltic magmas. When felsic domes form, they are emplaced within and on top of the conduit. If a dome forms and crystallizes enough early in an eruption, it acts as a plug on the system, denying the main mechanism of degassing. If this happens, it is common that the eruption will change from effusive to explosive, due to pressure build up below the lava dome.
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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 Miocene model suggested that the Indian-Asian collision is the major cause for Tibet's uplift, which is likely to be wrong due to reasons discussed above. In this model, the Lhasa tectonic block, equivalent to the southern Tibet, experienced initial uplift due to compressional force created when the Indian and Asian continent collided and the Tethys oceanic slab broke off (45—30 Ma). This is supported by the presence of Adakite in the Lhasa block. Adakite is an intermediate to felsic rock which is commonly related to oceanic subduction.
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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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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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No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed so much by the atmosphere that they do not create an impact crater. Incoming projectiles less than in diameter will fragment and burn up in the atmosphere before reaching the ground. The stratigraphically oldest tessera terrains have consistently lower thermal emissivity than the surrounding basaltic plains measured by Venus Express and Magellan, indicating a different, possibly a more felsic, mineral assemblage.
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Felsic intrusive xenoliths are a lot more common and usually originate from adjacent granitic intrusions, including those that form the Coast Mountains. More than 14 volcanic zones throughout the Northern Cordilleran Volcanic Province comprise xenoliths that originated from the Earth's mantle and are located mainly at the Yukon–Tanana Terrane, the Cache Creek Terrane and at volcanoes occupying the Paleozoic and Mesozoic Stikinia terrane. They consist of lherzolite, harzburgite, wehrlite, dunite, websterite and garnet composed pyroxenite. The highest and lowest temperatures recorded by mantle xenoliths increase to the south and decrease to the north.
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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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Although it is known that the Capitanian mass extinction occurred after Olson's Extinction and before the Permian–Triassic extinction event, the exact age of the Capitanian mass extinction remains controversial. This is partly due to the somewhat circumstantial age of the Capitanian–Wuchiapingian boundary itself, which is currently estimated to be approximately 259.1 million years old,Zhong, Y.-T., He, B., Mundil, R., and Xu, Y.-G. (2014). CA-TIMS zircon U–Pb dating of felsic ignimbrite from the Binchuan section: Implications for the termination age of Emeishan large igneous province.
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The spherules resemble the glassy chondrules (rounded granules) in carbonaceous chondrites, which are found in carbon-rich meteorites and lunar soils. Remarkably similar lithostratigraphic and chronostratigraphic structural sequences between these two cratons have been noted for the period between 3.5 and 2.7 billion years ago. Paleomagnetic data from two ultramafic complexes in the cratons showed that at the two cratons could have been part of the same supercontinent. Both the Pilbara and Kaapvaal cratons show extensional faults which were active about during felsic volcanism and coeval with the impact layers.
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It is of especial interest for astrobiology since this is one of the most Mars like environments on the Earth. In a 34-day experiment when placed in a Mars simulation chamber, it continued to photosynthesize, and it adapted to Mars conditions and even adapted physiologically by increasing its photosynthetic activity, and producing new growth. It is similar to Acarospora schleicheri, which grows on soil (terricolous lichen) and rarely on rock, and to Pleopsidium flavum. that grows in high elevations (montane to alpine) on vertical or overhanging hard felsic rock (e.g.
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A sample of granodiorite from Massif Central, France QAPF diagram for classification of plutonic rocks Mineral assemblage of igneous rocks Photomicrograph of thin section of granodiorite from Slovakia (in crossed polarised light) Granodiorite () is a phaneritic-textured intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. According to the QAPF diagram, granodiorite has a greater than 20% quartz by volume, and between 65% to 90% of the feldspar is plagioclase. A greater amount of plagioclase would designate the rock as tonalite. Granodiorite is felsic to intermediate in composition.
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The host rocks are mainly volcanic, with the felsic volcanic rocks pointing to a convergent setting such as an island arc or orogenic belt. Minor sedimentary beds such as chert and slate are found in VMS deposits and they indicate marine deposition, below the wave base. VMS deposits formed on the seafloor, in the same way that modern seafloor smokers are forming today. The most recent compilations of VMS deposits on land include about 1,100 deposits in more than 50 countries and 150 different mining camps or districts.
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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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Allanite (also called orthite) is a sorosilicate group of minerals within the broader epidote group that contain a significant amount of rare-earth elements. The mineral occurs mainly in metamorphosed clay-rich sediments and felsic igneous rocks. It has the general formula A2M3Si3O12[OH], where the A sites can contain large cations such as Ca2+, Sr2+, and rare-earth elements, and the M sites admit Al3+, Fe3+, Mn3+, Fe2+, or Mg2+ among others. However, a large amount of additional elements, including Th, U, Be, Zr, P, Ba, Cr and others may be present in the mineral.
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The Mattapan Volcanic Complex is a suite of Proterozoic felsic volcanic rocks, situated at the edge of the Boston Basin into the Blue Hills and lying unconformably atop the Dedham Granite. The complex is overlain by the Roxbury Conglomerate. In terms of its petrology, the rock types and compositions in the Mattapan Volcanic Complex are very similar to the Lynn Volcanic Complex and include ancient rhyolite and rhyodacite flows, some of which have porphyry characteristics, welded ash flows, tuff, breccia, extrusion domes and breccia pipes. The Mattapan Volcanic Complex rhyolites are thinner and have less varied composition and texture than the Lynn complex.
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Magmatism in the area during the Cretaceous resulted from easterly-directed subduction of the Farallon plates. This instigated felsic to intermediate arc-trench related magmatic activity spanning the Yukon Territory from 99 to 89 Ma. In central Yukon, these rocks were deformed in a northerly-directed, fold-and-thrust belt in the Jurassic to Cretaceous possibly due to more accretion on the West coasts. This deformation resulted in the development of three major faults in the area, the Dawson, Tombstone and Robert Service faults. The gold bearing Tombstone Plutonic suite of intrusions were emplaced into these rocks at 92 Mas.
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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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Several east-trending high-strain zones related to the Link Lake Deformation Zone, less than wide, are found in the intrusion, indicating that it formed at least before the last increment of strain along the Link Lake Deformation Zone. The dioritic intrusion might be the remains of a magma chamber that was the product of calc-alkaline feldspar-phyric felsic volcanism, the erupted products of which are mostly located in the Sherman Mine area. A dike intruding igneous rock exposed along Highway 11 immediately north of Temagami North. This dike is about wide At least three large granitoid intrusions penetrate the TGB.
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Volcanism 22 to 21 million years ago constructed the Coquihalla Volcanic Complex about northeast of Hope. It comprises volcanic and intrusive rocks that are calc-alkaline felsic to intermediate in composition. Coquihalla Mountain, the highest summit of the Bedded Range with an elevation of , is a major preserved stratovolcano and represents one of the few remaining Miocene volcanoes in southwestern British Columbia. As a result, the Coquihalla Volcanic Complex has been a subject of geological studies to annunciate the remains of what might have been an extensive cover of volcanic rocks during the early Miocene epoch.
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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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During the Neoproterozoic, Central Congo or Bas-Congo became a passive margin on which was deposited sediments. At the end of the Neoproterozoic, Bas-Congo was only affected by the Pan-African orogeny at 566 Ma to a limited extent protected by this passive margin and by the thickness of the craton. At 1000 Ma peralkaline magmatism initiated an early transtensional setting along the western edge of the Congo Craton. An LIP at 930–920 Ma was followed by felsic magmatism between 920–910 Ma which had a short emplacement interval and resulted in a thick sequence.
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Typical sial material, a Precambrian granite from St. Francis Mountains, Missouri, showing the potassium feldspar (felsic) matrix. In geology, the term 'sial' refers to the composition of the upper layer of the Earth's crust, namely rocks rich in silicates and aluminium minerals. It is sometimes equated with the continental crust because it is absent in the wide oceanic basins,Continental crust has been defined as That type of the Earth’s crust which underlies the continents and the continental shelves: it is equivalent to the sial. but "sial" is a geochemical term rather than a plate tectonic term.
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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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Large floating pumice blocks such as these observed in Kikai, Japan, in 1934–1935 may be comparable to lava balloons, but they are produced by eruptions of felsic magma, which are rich in silicates and lighter elements. By contrast, lava balloons are generally produced by eruptions of alkali basalt, although few basaltic eruptions produce them. Lava balloons are probably limited to a depth range of : too deep, and gas bubbles do not form; too shallow, and degassing fragments the rocks. Only a few sufficiently large balloons can rise all the way to the sea surface; smaller ones fill quickly with water and sink.
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An earlier phase of felsic volcanism during the Tertiary was followed during the Quaternary by more basaltic volcanism, often in the form of short-lived volcanic vents. Examples of this kind of volcanism are the Cima volcanic field, the San Francisco volcanic field (Arizona), the Southwest Nevada volcanic field (Nevada) and the Zuni-Bandera volcanic field (New Mexico). The Cima volcanic field is part of the Mojave Desert, which in turn belongs to the Basin and Range Province and features both mountains exceeding height which trend in southeast-northwest direction, with broad valleys between the mountains.
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Temperatures of have been estimated for the lava erupted by the Black Tank cone. The magma erupted in the field ultimately appears to originate from the lithospheric or asthenospheric mantle with little contribution of crustal components, unlike earlier felsic volcanism. Upwelling of asthenosphere material appears to be responsible for the volcanism at the end, possibly associated with the change in the tectonics of the region from subduction-dominated to tectonics of a transform boundary. Fractional crystallization, magma ponding in the crust, differences in the mantle sources and partial melting processes have been invoked to explain certain compositional differences in the erupted rocks.
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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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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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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 Big Dan Mine. Feldspar-phyric basalt lava flows contain tabular feldspar phenocrysts that range up to in cross section. Sills and dikes are widespread throughout the Arsenic Lake Formation and range in composition from ultramafic to felsic.
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The Iceland Lake Pluton, formerly known as the Ingall Lake Batholith, is a large granitic intrusion in Briggs and Strathcona townships of Temagami, Northeastern Ontario, Canada. It is one of the three separate granitoid intrusions that constitute the Temagami Greenstone Belt, consisting of rocks ranging from diorite to quartz monzonite. The age of the intrusion is estimated to be about 2,736 million years old, as well as an adjacent rhyolitic lava flow using the uranium–lead dating technique. This suggests that the Iceland Lake Pluton might be the remnants of a magma chamber of a volcano that erupted felsic magma.
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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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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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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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These exhalative sediments need a deep geothermal vent whose water is hot enough to dissolve gold from inside the crust. The hot water precipitates the dissolved minerals onto the ocean floor as fine crystals when it mixes with cold ocean floor water and cools off. A later, epithermal (cooler geothermal vents closer to the surface) process concentrated the gold further by dissolving other minerals surrounding the gold and leaving the gold behind. The South Pit's ore is made from fine sediments of felsic (rich in feldspar and quartz) ash from a volcano that flowed underwater and settled into thin laminated layers.
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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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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 mineralogy of an ignimbrite is controlled primarily by the chemistry of the source magma. The typical range of phenocrysts in ignimbrites are biotite, quartz, sanidine or other alkali feldspar, occasionally hornblende, rarely pyroxene and in the case of phonolite tuffs, the feldspathoid minerals such as nepheline and leucite. Commonly in most felsic ignimbrites the quartz polymorphs cristobalite and tridymite are usually found within the welded tuffs and breccias. In the majority of cases, it appears that these high-temperature polymorphs of quartz occurred post-eruption as part of an autogenic post- eruptive alteration in some metastable form.
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The Burwash Basin consists of turbidites interbedded with felsic to indermediate volcanic tuff. At 2634 Ma the Slave switched to a compressional regime and the Burwash Basin started to close, possibly due to shallow subduction from the NW or SE. By 2.6 Ga the Slave had collided with the much larger Sclavia, resulting in shortening and cross-folding over the craton. The presence of three rifted margins around the Slave, as well as similarly aged 3.3–3.5 Ga basement rocks, fuchsitic quartzite, and 2.9 Ga tonalites, suggest that the Dharwar, Zimbabwe, and Wyoming cratons were also part of Sclavia.
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This in turn produced thicker oceanic crust and thicker regions of underlying depleted lithospheric mantle. As such, the density of the lithosphere was reduced due to both differentiation of the crust from the mantle and the ensuing relative depletion of the residual mantle in Fe and Al. These expected properties have led to suggestions that oceanic lithosphere was so light that it subducted very shallowly or not at all. Scientists who favour this hypothesis argue that felsic material formed from hydrous partial melting of thickened oceanic crust in the root zones of oceanic plateaus, and not from subduction zones as generally believed.
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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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Hypothetical cross-section of an island arc volcano showing intrusions emplaced into the core of the volcano. During the development of porphyry-type ore, one or more intrusions would have generated a separate hydrothermal fluid phase and/or acted as a heat source to drive convection of meteoric waters (see red arrows). Porphyry deposits account for most of the copper and molybdenum world production, 60 and 95 percent of its supply respectively. Porphyry-type ore deposits form in hydrothermal fluid circulation systems developed above and around high-level, subvolcanic felsic to intermediate magma chambers and/or cooling plutons.
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They are characterized by greenstone belts, tonalites, and other high-grade metamorphic lithologies. The cratons are of significant importance in terms of mineral resources, with major deposits of gold, antimony, iron, chromium and nickel. A large volume of continental flood basalts erupted during the Oligocene, with the majority of the volcanism coinciding with the opening of the Red Sea and the Gulf of Aden approximately 30 Ma. The composition of the volcanics are a continuum of ultra-alkaline to tholeiitic and felsic rocks. It has been suggested that the diversity of the compositions could be partially explained by different mantle source regions.
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During the first eruptive period between 2,200,000 and 1,900,000 years ago, eruption of intermediate to felsic pyroclastic rocks occurred at the southern end of the massif. Basal breccia, perhaps from an exhumed vent, underlies andesite and tuffs, flows, lava domes and breccia of Devastator Peak. It has a maximum thickness of and overlies a high ridge of bedrock that formed between 251,000,000 and 65,500,000 years ago during the Mesozoic era. At the southwestern end of the massif, dacite with sparse phenocrysts (large and conspicuous crystals) of quartz, plagioclase and hornblende represents a thick remnant of subhorizontal lava flows.
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The felsic shield-building stage began with the eruption of phonolite, trachyte, phonolitic trachyte, quartz-trachyte and rhyolite lava. Subsequent volcanism of the pre-explosive phase produced a basal sequence of aphyric trachyte lava flows and domes with minor altered flow-banded rhyolite, sulfide-bearing rhyolitic tuffs and a few thin hawaiite lava flows. This activity was concentrated at the summit of the volcano as shown by the increasing thickness of volcanic material towards the summit. A hydrothermally altered aphyric trachyte dike, which forms a narrow ridge linking Mount Downton and Itcha Mountain, might have been the source for these eruptions.
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The high frequency of gold mineralization in and near the Net Lake-Vermilion Lake Deformation Zone suggests that this deformation zone may very well also contain gold deposits; at least 11 have been discovered within a length of the deformation zone. The gold deposits are found in many rock types, indicating a stronger gold-bearing system with the potential of larger gold deposits. A number of gold-pyrite deposits exist in felsic volcanic rocks overlying the Older Volcanic Complex, near and on the northwestern part of the Net Lake-Vermilion Lake Deformation Zone. These deposits were likely formed during the creation of the Net Lake-Vermilion Lake Deformation Zone.
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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 primary disadvantage to K–Ca dating is the abundance of calcium in most minerals; this dating method cannot be used on minerals with a high preexisting calcium content, as the radioactively added calcium will increase calcium abundance in the sample only very slightly. As such, K–Ca dating is effective only in circumstances where K/Ca>50 (in a potassium-enriched, calcium-depleted sample). Examples of such minerals include lepidolite, potassium-feldspar, and late-formed muscovite or biotite from pegmatites (preferably older than 60 Ma). This method is also useful for zircon-poor, felsic-to-intermediate igneous rocks, various metamorphic rocks, and evaporite minerals (i.e. sylvite).
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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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A U-shaped valley of Level Mountain with extensive elevated plateau in the foreground After the basal shield volcano was constructed, several vents produced oversaturated, undersaturated, peralkaline and metaluminous lavas. This tremendous variation in the erupted magmas and influence of adjacent vents gave rise to a high and volumnous complex bimodal stratovolcano centrally located atop the shield. Mapping indicates that the headwaters of Kakuchuya Creek were the site of this large stratovolcano cap and that it grew over in elevation. Volcanic rocks of felsic composition, notably peralkaline trachyte and comendite, were the primary products comprising this edifice, forming more than 80% of its volume.
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In the area of Snofleld Lake in the northern part of the Slave Province, the remains of Archean stromatolites are preserved in a dolomite unit between felsic volcanic and greywacke-mudstone turbidites, some of the earliest evidence of life, forming in the shallows around volcanic islands. Around 1.27 billion years ago in the Proterozoic, a series of major magmatic events affected the region, referred to as "Mackenzie magmatic event," by some geologists. In the Coppermine River Province, tholeiite flood basalts emplaced at the same time over a rapid span of five million years. Strontium-neodymium- lead analysis indicates that the rocks included older, partially melted basement rocks.
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TTG is a prevalent rock type in archean formations. All 3 regions contain an abundance of Archean felsic volcanic rocks, including tonalite, trondhjemite and granodiorite (TTG) series rocks, with minor granulite to amphibolite facies gneiss complexes, which means that the original characters of the rocks has been disturbed by at least one ductile deformation at deep crustal conditions. Eoarchean geology is important in investigating earth's tectonic history. It is because the earth had just undergone an transformation to the present-day-similar convective mode and lithosphere from a magma ocean in Hadean Eon, to either a protoplate tectonics or an unstable stagnant lithosphere lid at its infant stages.
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Additionally, the removal of the higher melting point material will raise the concentration of felsic components such as silicates potentially making the magma more viscous, adding to the explosive nature of the eruption. The area around the volcano is now densely populated. The government emergency plan for an eruption therefore assumes that the worst case will be an eruption of similar size and type to the 1631 VEI 4 eruption. In this scenario, the slopes of the volcano, extending out to about from the vent, may be exposed to pyroclastic surges sweeping down them, whilst much of the surrounding area could suffer from tephra falls.
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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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Lamproites form from partially melted mantle at depths exceeding 150 km. The molten material is forced to the surface in volcanic pipes, bringing with it xenoliths and diamonds from the harzburgitic peridotite or eclogite mantle regions where diamond formation is stabilized. Recent research, for example on the lamproites at Gaussberg in Antarctica, and lead-lead isotope geochemistry have revealed that the source of lamproites may be transition zone melts of subducted lithosphere which has become trapped at the base of the lithospheric mantle. This observation also reconciles the depth of melting with the peculiar geochemistry, which is most easily explained by melting of already felsic material under deep mantle conditions.
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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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In addition felsic pyroclastic rocks are very common in places and one sandstone-conglomerate lava flow can be found. The sedimentary breccia is dominated by pebble to boulder size angular metasedimentary stratas, and a few crystal tuff layers that contain about 1% biotite, the only such high amount of a typically trace mineral outside of Rothea formation in the Extracaldera sequence. A pumice-ridden lapilli-tuff section near the believed top section additionally has a 1% composition of the mineral amphibole. The exposed portion of the flows loosely flank the slopes of the volcano on the left and right, and are represented by bright orange on the map.
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Photomicrograph of a porphyritic-aphanitic felsic rock, from the Middle Eocene in the Blue Ridge Mountains of Virginia. Plagioclase phenocrysts (white) and hornblende phenocryst (dark; intergrown with plagioclase) are set in a fine matrix of plagioclase laths that show flow structure. Rocks can be classified according to the nature, size and abundance of phenocrysts, and the presence or absence of phenocrysts is often noted when a rock name is determined. Aphyric rocks are those that have no phenocrysts, or more commonly where the rock consists of less than 1% phenocrysts (by volume);Some use a 1% boundary condition, and , while others suggest a limit of 5%.
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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 national park’s distinctive hard black boulders (often termed granite) and range are composed of the igneous felsic intrusive Trevethan Granodiorite which is predominantly a white to grey, medium-grained, porphyritic biotite monzogranite to granodiorite. The age of the intrusive is Late Permian and has been dated from 259.1 to 251.902 million years old. The Trevethan Granodiorite was originally magma that slowly solidified under the earths crust. The softer land surfaces above the solidified magma eroded away over time, leaving the magma's fractured top to be exposed as a mountain of grey granite boulders blackened by a film of microscopic blue-green algae growing on the exposed surfaces.
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Low-temperature, but high-pressure conditions led rocks to reach eclogite-grade on the sequence of metamorphic facies. The added presence of diamonds and felsic gneiss indicates deep burial up to 100 kilometers below the surface. The China Continental Scientific Drilling Project was approved in China's ninth Five-Year Plan in 1997, with the CCSD-1 well inaugurated on 25 June 2001 drilling into the Dabie-Sulu orogen at Lianyungang City, Jiangsu Province. The goal of the project throughout the 2000s was to collect data about rheology and mantle mineralogy, as well as study processes similar to those in the center of the Himalayas, but at lower cost.
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Effusive eruptions are most common in basaltic magmas, but they also occur in intermediate and felsic magmas. These eruptions form lava flows and lava domes, each of which vary in shape, length, and width. Deep in the crust, gasses are dissolved into the magma because of high pressures, but upon ascent and eruption, pressure drops rapidly, and these gasses begin to exsolve out of the melt. A volcanic eruption is effusive when the erupting magma is volatile poor (water, carbon dioxide, sulfur dioxide, hydrogen chloride, and hydrogen fluoride), which suppresses fragmentation, creating an oozing magma which spills out of the volcanic vent and out into the surrounding area.
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During that time period, a number of volcanic eruptions occurred in Antarctica as recorded by ash layers in ice; this coincides with the coldest period of the Wisconsin glaciation and it is possible that the effects of ash clouds from the Antarctic eruptions caused this period of cold global temperatures. On the other hand, it is also possible that growing ice sheets during this period compressed magma chambers and thus triggered explosive eruptions. Toney Mountain lies in Marie Byrd Land, a tectonically and volcanically active region of Antarctica. There, a layer of basaltic rocks up to thick underlie a series of felsic volcanic edifices.
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The rocks in the North China craton consist of Precambrian (4.6 billion years ago to 541 million years ago) basement rocks, with the oldest zircon dated 4.1 billion years ago and the oldest rock dated 3.8 billion years ago. The Precambrian rocks were then overlain by Phanerozoic (541 million years ago to present) sedimentary rocks or igneous rocks. The Phanerozoic rocks are largely not metamorphosed. The Eastern Block is made up of early to late Archean (3.8-3.0 billion years ago) tonalite-trondhjemite-granodiorite gneisses, granitic gneisses, some ultramafic to felsic volcanic rocks and metasediments with some granitoids which formed in some tectonic events 2.5 billion years ago.
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Arenal Volcano, Costa Rica, is a stratovolcano. Volcanoes are the primary landforms built by repeated eruptions of lava and ash over time. They range in shape from shield volcanoes with broad, shallow slopes formed from predominantly effusive eruptions of relatively fluid basaltic lava flows, to steeply-sided stratovolcanoes (also known as composite volcanoes) made of alternating layers of ash and more viscous lava flows typical of intermediate and felsic lavas. A caldera, which is a large subsidence crater, can form in a stratovolcano, if the magma chamber is partially or wholly emptied by large explosive eruptions; the summit cone no longer supports itself and thus collapses in on itself afterwards.
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The northwestern parts of the Shield, located roughly north and west of Sudbury, are known as the Superior Province; this is the largest of the three sections, covering about 70% of the Shield portion in Ontario. This region is more than 2.5 billion years old and is composed of felsic intrusive rocks. In the northernmost parts of the Superior Province, the geology of the region is dominated by granite and gneiss rocks. The central region of the Shield, known as the Grenville Province and located south of Sudbury, is 1.0 to 1.6 billion years old and is dominated by sedimentary rocks showing evidence of being subjected to metamorphism.
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Within the metamorphic belts, pegmatite tends to concentrate around granitic bodies within zones of low mean strain and within zones of extension, for example within the strain shadow of a large rigid granite body. Similarly, pegmatite is often found within the contact zone of granite, transitional with some greisens, as a late-stage magmatic- hydrothermal effect of syn-metamorphic granitic magmatism. Some skarns associated with granites also tend to host pegmatites. Aplite and porphyry dikes and veins may intrude pegmatites and wall rocks adjacent to intrusions, creating a confused sequence of felsic intrusive apophyses (thin branches or offshoots of igneous bodies) within the aureole of some granites.
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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 oldest rocks in Arkansas are igneous granites encountered in deep wells in the Ozarks and the northern part of the Mississippi Embayment, dated to be 1.4 billion years old. These felsic rocks likely formed sometime soon after the breakup of the supercontinent Columbia, into its component continents, including Laurentia, which today forms the stable basement rocks of most of North America. The Precambrian, including the Archean and Proterozoic eons is poorly understood in Arkansas, but the entire state is believed to be underlain by deep, igneous and metamorphic crystalline basement rock. In the Ouachita region, geologists have found igneous and metamorphic Precambrian erratic boulders as well as metamorphosed igneous rock intrusions.
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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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Magma mixing is the process by which two magmas meet, comingle, and form a magma of a composition somewhere between the two end-member magmas. Magma mixing is a common process in volcanic magma chambers, which are open-system chambers where magmas enter the chamber, undergo some form of assimilation, fractional crystallisation and partial melt extraction (via eruption of lava), and are replenished. Magma mixing also tends to occur at deeper levels in the crust and is considered one of the primary mechanisms for forming intermediate rocks such as monzonite and andesite. Here, due to heat transfer and increased volatile flux from subduction, the silicic crust melts to form a felsic magma (essentially granitic in composition).
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Komatiite magma is extremely dense and unlikely to reach the surface, being more likely to pool lower within the crust. Modern (post-2004) interpretations of some of the larger olivine adcumulate bodies in the Yilgarn craton have revealed that the majority of komatiite olivine adcumulate occurrences are likely to be subvolcanic to intrusive in nature. This is recognised at the Mt Keith nickel deposit where wall-rock intrusive textures and xenoliths of felsic country rocks have been recognised within the low-strain contacts. The previous interpretations of these large komatiite bodies was that they were "super channels" or reactivated channels, which grew to over 500 m in stratigraphic thickness during prolonged volcanism.
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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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Mount Hasan has been active for the last 13 million years, with the , Paleo-Hasan, Mesovolcano and Neovolcano stages during the Miocene, Miocene-Pliocene and Quaternary; the older two stages might actually not be part of Mount Hasan at all. Aside from the felsic central vent volcanism, basaltic volcanism also took place at Mount Hasan throughout its activity; this activity has been dated to 120,000, 65,000 and the most recent event 34,000 years ago. is the oldest (13 million years) volcanic structure, it is among the oldest volcanoes of the Central Anatolian volcanic province. This volcano is a small sized volcano with a caldera which crops out on the southwestern side of Mount Hasan.
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Close to the Mount Skokum gold mine, the south Dawson Range and the Sifton Range west of Whitehorse have the Eocene felsic volcanic rocks of the Skukum Group. In the Oligocene, the Yakutat terrane, a section of Cretaceous flysch and mélange together with Paleogene basalt from the Pacific Plate split off the western edge of the Canadian Cordillera and added on to the western edge of the Yukon. The Chugach terrane, with siltstone, argillite and sandstone trench fill from the Cretaceous and early Paleogene layered on top of the Yakutat terrane along the Border Ranges Fault. The fault is interpreted as the subduction zone fault shifted onto land by the Yakutat collision.
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The types of minerals present in volcanic ash are dependent on the chemistry of the magma from which it erupted. Considering that the most abundant elements found in silicate magma are silicon and oxygen, the various types of magma (and therefore ash) produced during volcanic eruptions are most commonly explained in terms of their silica content. Low energy eruptions of basalt produce a characteristically dark coloured ash containing ~45–55% silica that is generally rich in iron (Fe) and magnesium (Mg). The most explosive rhyolite eruptions produce a felsic ash that is high in silica (>69%) while other types of ash with an intermediate composition (e.g., andesite or dacite) have a silica content between 55–69%.
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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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Plate tectonics of the Coast Range Arc about 75 million years ago Volcanism in the arc began during the Late Cretaceous period 100 million years ago based on andesitic composition of the Early Cretaceous volcanic sections and their close temporal and spatial association with masses of felsic intrusive igneous rock with phaneritic texture called tonalite. The basement of the Coast Range Arc was likely Early Cretaceous and Late Jurassic intrusions. Stratigraphic and field relations in the arc suggest that the Coast Range Arc was created on Stikinia, a geologic feature that formed in an older volcanic arc environment during the Paleozoic and Mesozoic periods. Plate distribution between 64 and 74 million years ago.
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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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Subsequently, felsic magmatism and explosive eruption resumed. All of this has been thought to be linked to changes in the stress field of the volcanoes and their plumbing system caused by unloading of ice. As deglaciation proceeded faster in the north there is an apparent lag in the onset of this behavior among volcanoes. The period of less explosive volcanism spanned from about 17–4 ka BP in Villarrica (39°25' S), 10–2 ka BP in Mocho- Choshuenco (39°55' S), 6–2 ka BP in Puyehue-Cordón Caulle (40°35' S) and Calbuco (41°20' S). Various ephemeral proglacial lakes existed during the deglaciation including Paleolake Tehuelche in Torres del Paine (51° S).
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Pleopsidium flavum (gold cobblestone lichen)The Laws Field Guide to the Sierra Nevada, John Muir Laws , 2007 is a distinctively colored, bright lemon-yellow to chartreuseCrustose Rock Lichens, Wayne P. Armstrong, Wayne's World online textbook of natural history, crustose lichen that grows in high elevations (montane to alpine) on vertical or overhanging hard felsic rock (e.g. granite) in western North America.Mosses Lichens & Ferns of Northwest North America, Dale H. Vitt, Janet E. marsh, Robin B. Bovey, Lone Pine Publishing Company, Its thallus grows in a circular outwardly radiating pattern (crustose placoidioid), with 1mm wide lobed edges. This is the identity of the vivid, lime-green lichens often photographed on granite boulders in the Wichita Mountains Wildlife Refuge of Oklahoma.
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Although extensive rifting has not yet been recognized in the Northern Cordilleran Volcanic Province, volcanism throughout the past 1.6 million years is possibly due to repetitive upper mantle upwelling and adjacent transtension throughout the Queen Charlotte Fault, accommodated partly by numerous east-west trending fault zones that extend all through the Northern Cordilleran Volcanic Province. The volcanics comprising the Northern Cordilleran Volcanic Province are consistent with the rifting environment. Alkaline basalt, lesser hawaiite and basanite magmas from effusive eruptions create the massive shield volcanoes and small cinder cones throughout the volcanic province, several of which comprise lherzolite magma. Felsic magmas from more viscous eruptions create the massive central volcanoes and largely consist of trachyte, pantellerite and comendite lavas.
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Metal sulfide ores were formed in two different epochs, lead and zinc sulfide ores were formed in the sedimentary rocks around 1.8 Ga years ago during Paleoproterozoic phase. The tectonic setting of Zinc-lead-copper sulfides mineralisation in Delhi supergroup rocks in Haryana-Delhi were formed in mantle plume volcanic action around 1 Ga years ago covering Haryana and Rajasthan during mesoproterozoic. In the southern part of Aravalli supergroup arc base metal sulfides were generated near the subduction zone on the western fringe and in zones of back- arc extension to the south-east. Continued subduction produced W-Sn (Tungsten- Tin) mineralisation in S-type (sedimentary unmetamorphosed rock) felsic (volcanic rock) plutons (underground crystallised solidified magma).
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The regional, local and property geology of the Rosemont deposit consists of Precambrian sedimentary and intrusive rocks, which form the regional basement under a Palaeozoic sequence of quartzites, siltstones, and carbonate rocks. Sedimentary deposition ceased for a time during uplift and formation of a widespread unconformity in the early Mesozoic, and then resumed with the deposition of continental and shallow marine deposits.Geology and Seismotectonic Review, Vector Colorado Subsequent granitic intrusions and felsic volcanic eruptions dominated the late Mesozoic and early Cenozoic, corresponding to the Laramide Orogeny when most of the porphyry copper deposits of the region formed. Compressional tectonics during the Laramide Orogeny created both low-angle thrust faults and high-angle strike-slip faults.
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The Interagency Volcanic Event Notification Plan (IVENP) was created to outline the notification procedure of some of the main agencies that would respond to an erupting volcano in Canada, an eruption close to the Canada–United States border or any eruption that would affect Canada. Because of the remote location of the Itcha Range, future eruptions are not a major hazard. Future volcanism is most likely in the form of basaltic cinder cones, but eruptions of felsic magma can not be ruled out. The most immediate hazard relating to future eruptions is of local concern only and includes the possibility of forest fires by lava flows and the disruption of local air traffic if an eruption column is produced.
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The central portion of the Anahim Volcanic Belt contains three complex shield volcanoes, known as the Rainbow, Ilgachuz, and Itcha ranges. These fairly dissected shield volcanoes lie on the northern end of the Chilcotin Group lava plateau and distal lava flows at the margins of the shield volcanoes merge imperceptibly with flat- lying lava flows comprising the Chilcotin Group lava plateau. Unlike the Chilcotin Group basalt, which is not associated with any felsic derivatives, the volcanoes of the central Anahim Volcanic Belt are markedly bimodal, comprising a mixed assemblage of basalt and peralkaline silicic rocks. While volcanoes of the Anahim Volcanic Belt appear to merge laterally with the Chilcotin Group lavas, the particular nature and connection between the Anahim Volcanic Belt and the Chilcotin Group is unknown.
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Montana Mountain is a deeply eroded Late Cretaceous stratovolcano located south of Carcross, Yukon, Canada. As well as its main peak, the mountain includes many sub-peaks and contains felsic pyroclastics and flows;Jurassic to Cretaceous volcanics Retrieved on 2007-07-04 typically altered and orange- weathering. Montana Mountain was formed when the ancient Kula Plate was subducting under southwestern Yukon during the Late Cretaceous period. A flurry of quartz mining activity took place on Montana Mountain starting in 1899, peaking in 1905-1906 when American mining promoter John Conrad consolidated claims on Montana Mountain and built three tramways to carry the ore back down, including a 4-mile-long one from Windy Arm on Tagish Lake to the Mountain Hero mine.
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The Napier Complex is among the most ancient terrestrial terranes on Earth. Its evolution is characterized by high- grade metamorphism and several strong deformations. At least four distinct tectonothermal events occurred in the Archaean Eon: # 3.8 billion years ago: occurrence of initial felsic igneous activity over a long period of time # 3.0 billion years ago: emplacement of charnockite at Proclamation Island # 2.8 billion years ago: occurrence of a very-high grade discrete tectonothermal event (a UHT metamorphic event) # 2.5 billion years ago: occurrence of a subsequent, protracted high-grade tectonothermal event Much of the East Antarctic craton was formed in the Precambrian period by a series of tectonothermal orogenic events. Napier orogeny formed the cratonic nucleus approximately 4 billion years ago.
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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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The Paipa–Iza volcanic complex is a volcanic field of Late Pliocene to Early Pleistocene age on the Altiplano Cundiboyacense in the Eastern Ranges of the Colombian Andes. It is the northernmost volcanic complex of the Andean Volcanic Belt with Fueguino in Tierra del Fuego, Chile, at the opposite end of the Andean mountain belt. The complex, comprising mainly felsic extrusive volcanic rocks as rhyolites, also is the only confirmed volcanic province in the Eastern Ranges, with traces of probably contemporaneous explosive volcanic activity in the vicinity of Guatavita, Cundinamarca. The Paipa-Iza volcanic field is important as a touristic site with thermal baths in both Paipa and Iza and is being studied for the potential of geothermal energy production and for the extraction of uranium in the area.
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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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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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This is exemplified by the Mount Keith MKD5 orebody, near Leinster, Western Australia, which has recently been reclassified according to a subvolcanic intrusive model. Extremely thick olivine adcumulate piles were interpreted as representing a 'mega' flow channel facies, and it was only upon mining into a low-strain margin of the body at Mount Keith that an intact intrusive-type contact was discovered. Similar thick adcumulate bodies of komatiitic affinity which have sheared or faulted-off contacts could also represent intrusive bodies. For example, the Maggie Hays and Emily Ann ore deposits, in the Lake Johnston Greenstone Belt, Western Australia, are highly structurally remobilised (up to 600 m into felsic footwall rocks) but are hosted in folded podiform adcumulate to mesocumulate bodies which lack typical spinifex flow-top facies and exhibit an orthocumulate margin.
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A unique geological feature of Battle Mountain is that the western slope outcrops are composed entirely of alkalai feldspar granite, while the eastern slope up to and including the summit is entirely rhyolitic. This provides strong evidence of a theorized lateral explosive eruption event centered on the eastern slope at approximately 704 Ma as proposed by Woolman (2016). Further mathematical geology evidence which supports this theory includes a paleaogeographic reconstruction of the mountain by Woolman utilizing artificial neural networks and Markov chain geostatistical models including period climate condition- based soil erosion rates, Kirkby's hillslope movement evolution equations and recursive biogeochemical soil erosion rates in felsic granitic conditions. The result was the digital reconstruction image shown on the left, indicating what Battle Mountain may have looked like 704 million years ago on the western slope.
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At the Younger Volcanic Complex, gold exists in quartz veins containing base metal sulfides. It is also known to exist in pyrite associated with deformed magnetite-rich iron formations, sericitized and carbonatized felsic volcanic rock, quartz-pyrrhotite-chalcopyrite-pentlandite-pyrite zones within deformation zones and in north-trending, chloritized shear zones containing arsenopyrite, pyrrhotite, pyrite and chalcopyrite. Samples of pyrite in quartz obtained from a wide quartz vein at Beanland Mine A variety of iron, copper, arsenic and zinc ores such as arsenopyrite, pyrrhotite, pyrite and chalcopyrite with sphalerite, are present as small veins and in quartz veins throughout north-trending shear zones that cut the iron-rich tholeiitic basalts of the Arsenic Lake Formation. Dikes composed of quartz- feldspar porphyry run parallel to or lie within the shear zones and are cut by the mineralization.
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The laser studies create plasma, and the results are suggestive that constraining inner core conditions will depend on whether the inner core is a solid or is a plasma with the density of a solid. This is an area of active research. In early stages of Earth's formation about 4.6 billion years ago, melting would have caused denser substances to sink toward the center in a process called planetary differentiation (see also the iron catastrophe), while less-dense materials would have migrated to the crust. The core is thus believed to largely be composed of iron (80%), along with nickel and one or more light elements, whereas other dense elements, such as lead and uranium, either are too rare to be significant or tend to bind to lighter elements and thus remain in the crust (see felsic materials).
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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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Dendi Caldera, a collapsed volcano in the mountain region The Ethiopian Highlands began to rise 75 million years ago, as magma from the Earth's mantle uplifted a broad dome of the ancient rocks of the Arabian- Nubian Shield. The opening of the Great Rift Valley split the dome of the Ethiopian Highlands into three parts; the mountains of the southern Arabian Peninsula are geologically part of the ancient Ethiopian Highlands, separated by the rifting which created the Red Sea and Gulf of Aden and separated Africa from Arabia. Around 30 million years ago, a flood basalt plateau began to form, piling layers upon layers of voluminous fissure-fed basaltic lava flows. Most of the flows were tholeiitic, save for a thin layer of alkali basalts and minor amounts of felsic (high-silica) volcanic rocks, such as rhyolite.
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With this appreciation, the author has concluded that the igneous activity of St. Mary's Islands may represent Cretaceous-Tertiary igneous activity. In a further analysis of the age of the break-up of Greater India (India plus Seychelles) and Madagascar it has been inferred to have occurred in the Upper Cretaceous at 88 Ma. The strength of this inference is based on the approach that the Felsic volcanics (rhyolites and Rhyodacites) of the St. Mary's Islands (SMI), Southern India, were originally interpreted as a distant outlier of the 66 Ma Deccan volcanic province of west–central India, comprising dominantly flood basalts. Later studies had dated it at 93 Ma by the K-Ar dating technique. Since the technique used was a simple use of an average of five out of six widely varying dates and arbitrary data selectivity chosen, the results were not considered reliable.
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Iron oxide copper gold (IOCG) deposits are considered to be metasomatic expressions of large crustal-scale alteration events driven by intrusive activity. The deposit type was first recognised, though not named as IOCG, by discovery and study of the supergiant Olympic Dam copper-gold-uranium deposit (Olympic Dam mine), and South American examples. IOCG deposits are classified as separate to other large intrusive related copper deposits such as porphyry copper deposits and other porphyry metal deposits primarily by their substantial accumulations of iron oxide minerals, association with felsic-intermediate type intrusives (Na-Ca rich granitoids), and lack of the complex zonation in alteration mineral assemblies commonly associated with porphyry deposits. The relatively simple copper-gold +/- uranium ore assemblage is also distinct from the wide spectrum of Cu-Au-Ag-Mo-W-Bi porphyry deposits, and there is often no metal zonation within recognised examples of IOCG deposits.
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The Kam Group is a 0.3–6 kilometre thick sequence that overlies banded iron formations of the Central Slave Cover Group. The contact between these two groups is not well preserved due to the intrusion of gabbro sills and moderate shearing. The Kam group is separated into a lower and upper group based on the existence of a thin felsic volcaniclastic layer (Ranney Chert) dated at 2722 Ma. The lower Kam group consists of the Chan Formation which contains flows of pillowed basalts intruded by a series of gabbroic sills and dikes that were produced in an extensional back-arc basin setting. Sedimentary rocks exposed in the northern part of the formation are between 2.84 and 2.80 Ga. The Upper Kam Group contains three formations deposited between 2772 and 2701 Ma. It is composed mainly of intermediate and basaltic volcanic rocks with thin intercalated rhyolite tuff layers and minor komatiite flows.
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The often rapid accumulation of unconsolidated pyroclastic material on steep sideslopes tends to be inherently unstable over time; pyroclastic dams may be emplaced by the landsliding of such material into rivers and streams. Pyroclastic material, given sufficient time to consolidate or 'weld' into hard rock, produce assemblages variously classified as ignimbrites, variously brecciated or agglomerated, along with various types of tuffs and volcanic ash, and are mostly of felsic composition. While evidence of pyroclastic dams occur within the geologic record,Andrews, Graham D.M., Russell, J. Kelly, and Stewart, Martin L., LAHAR FORMATION BY CATASTROPHIC COLLAPSE OF A PYROCLASTIC DAM: HISTORY, VOLUME, AND DURATION OF THE 2360 BP SALAL LAKE, MOUNT MEAGER, BRITISH COLUMBIA, CANADA, (Abstract) Geological Society of America, 2009 they are best known and studied in relation to recent and current volcanic eruptions. Examples worldwide include associations with El Chichon in Mexico,El Chichon, Mexico and the Karymsky Volcano in Russia.
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Its formation has been attributed to the thermal metamorphosis process due to which the rocks attained the andalusitic horn-felsic form. Tegar is one of the villages in the Nubra Valley (average elevation of about 10,000 ft), known as the village of alfalfa and fertile soil, on the silk route, and caravans used to halt here while travelling from between Central Asia and Kashmir and the locals used to lease out grazing land to the traders so that their livestock can graze ; the other important villages on this route are Khardong, Khalsar, Tirit, Sumoor, Pinchemik, Chamshein, Tirisha and Panamic (see map). The principal hotels in the village are Lchang Nang Retreat, Hotel Yarab Tso and the Hotel Rimo which are about 500 m away from the village. It is under the Diskit administrative Sub-Division and the main approach road to the valley passes through the highest Khardung La mountain pass (18,380 ft), which is accessible throughout the year.
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A system of regional faults, although partially obscured by the volcanic product, has two distinct orientations: a NNE-SSW alignment that could be an extension of Cameroon line, and a NNW-SSE alignment that could extend to the Great Rift Valley; however, the relationship between these fault systems has not been conclusively demonstrated. More recently in geologic time, the volcanic activity has deposited dacite and ignimbrite, as well as trachyte and trachyandesite. This trend towards the production of more felsic, viscous lavas could be a sign of a waning mantle plume. Animation showing the phases of volcanic activity in the Tibesti Mountains Satellite image of the volcanic field on Tarso Tôh, which includes 150 cinder cones, two maars, and several basalt lava channels Satellite image of the more recent lava rock, in black, with Toussidé volcano (center) and the Trou au Natron crater (bottom right) The volcanic activity took place in several phases.
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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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Ilmenite from Froland, Aust-Agder, Norway; 4.1 x 4.1 x 3.8 cm Ilmenite and hematite under normal light Ilmenite and hematite under polarized light Ilmenite most often contains appreciable quantities of magnesium and manganese and the full chemical formula can be expressed as (Fe,Mg,Mn,Ti)O3. Ilmenite forms a solid solution with geikielite () and pyrophanite () which are magnesian and manganiferous end-members of the solid solution series. Although there appears evidence of the complete range of mineral chemistries in the (Fe,Mg,Mn,Ti)O3 system naturally occurring on Earth, the vast bulk of ilmenites are restricted to close to the ideal composition, with minor mole percentages of Mn and Mg. A key exception is in the ilmenites of kimberlites where the mineral usually contains major amounts of geikielite molecules, and in some highly differentiated felsic rocks ilmenites may contain significant amounts of pyrophanite molecules. At higher temperatures it has been demonstrated there is a complete solid solution between ilmenite and hematite.
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During this era, the earliest global-scale continent-continent collision belts developed. These continent and mountain building events are represented by the 2.1–2.0 Ga Trans-Amazonian and Eburnean orogens in South America and West Africa; the ~2.0 Ga Limpopo Belt in southern Africa; the 1.9–1.8 Ga Trans-Hudson, Penokean, Taltson–Thelon, Wopmay, Ungava and Torngat orogens in North America, the 1.9–1.8 Ga Nagssugtoqidian Orogen in Greenland; the 1.9–1.8 Ga Kola–Karelia, Svecofennian, Volhyn-Central Russian, and Pachelma orogens in Baltica (Eastern Europe); the 1.9–1.8 Ga Akitkan Orogen in Siberia; the ~1.95 Ga Khondalite Belt and ~1.85 Ga Trans-North China Orogen in North China. These continental collision belts are interpreted as having resulted from one or more 2.0–1.8 Ga global-scale collision events that then led to the assembly of a Proterozoic supercontinent named Columbia or Nuna. Felsic volcanism in what is now northern Sweden led to the formation of the Kiruna and Arvidsjaur porphyries.
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It formed due to extensional cracking, faulting, and rifting of the North American Plate as the Pacific Plate grinds and slides past the Queen Charlotte Fault, unlike subduction that produces the volcanoes in Japan, the Philippines, and Indonesia. The region has Canada's largest volcanoes, much larger than the minor stratovolcanoes found in the Canadian portion of the Cascade Volcanic Arc. Several eruptions are known to have occurred within the last 400 years. Mount Edziza is a huge volcanic complex that erupted several times in the past several thousand years and has formed several cinder cones and lava flows. The complex comprises the Mount Edziza Plateau, a large volcanic plateau (65 km long and 20 km wide) made of predominantly basaltic lava flows with four large stratovolcanoes built on top of the plateau. The associated lava domes and satellite cones were constructed over the past 7.5 million years during five magmatic cycles beginning with eruption of alkali basalts and ending with felsic and basaltic eruptions as late as 1,340 years ago.
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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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