However, a cinder cone in the middle of the shield could be much younger, perhaps as young as the basanites at Nazko Cone to the east, which were erupted 340,000 to 7,100 years ago. The older basanites in the Itcha Range may have been erupted contemporaneously with the late feldspar hawaiites.
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Phenocrysts include olivine, plagioclase and pyroxene. Alkali basalts have few vesicles and a gray colour. Basanites contain more olivine and less plagioclase/pyroxene phenocrysts. No non- basaltic magmas have been erupted at Longgang.
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The word "basalt" is ultimately derived from Late Latin basaltes, a misspelling of Latin basanites "very hard stone", which was imported from Ancient Greek βασανίτης (basanites), from βάσανος (basanos, "touchstone") and perhaps originated in Egyptian bauhun "slate". The modern petrological term basalt describing a particular composition of lava-derived rock, originates from its use by Georgius Agricola in 1546 in his work De Natura Fossilium. Agricola applied "basalt" to the volcanic black rock beneath the Bishop of Meißen's Stolpen castle, believing it to be the same as the "basaniten" described by Pliny the Elder in AD 77 in Naturalis Historiae.
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Alkali basalts erupted after the cessation of subduction. These range in age from the tephrites at Mount Pinafore (5.5-7.6 Ma), to the basanites at Rothschild Island (5.5 Ma) and Hornpipe Heights (2.5 Ma), to the alkali and olivine basalts on Beethoven Peninsula (<1-2.5 Ma).
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Those leucite rocks which contain abundant essential plagioclase feldspar are known as leucite tephrites and leucite basanites. The former consist mainly of plagioclase, leucite and augite, while the latter contain olivine in addition. The leucite is often present in two sets of crystals, both porphyritic and as an ingredient of the ground mass. It is always idiomorphic with rounded outlines.
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This brought magmatism commonly associated with rifting and doming to the Freemans Cove area. Nearly all magmatic activity was confined to regions within the fault zone and involved the emplacement of dikes, sills, small volcanic plugs and agglomeratic vents. The magmas are chemically bimodal, consisting mainly of nephelinites or larnite-normative nephelinites and basanites along with lesser olivine melilite nephelinites, phonolites and tholeiitic and alkali basalts.
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The petrology of the Honolulu Volcanics is well studied. The volcanic rocks of the Honolulu Volcanics are diverse; they include alkali basalts, melilite and nepheline basalts, basanites, melilite, nephelinite and websterite, and form an alkaline-nephelinite suite. The variations in composition reflect distinct proportions of melts produced from parent rocks. Phenocrysts include augite, labradorite, olivine and plagioclase; additionally spinels are found in the rocks.
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The leucite-tephrites and leucite-basanites of Vesuvius and Somma are familiar examples of this class of rocks. They are black or ashy-grey in color, often vesicular, and may contain many large grey phenocrysts of leucite. Their black augite and yellow green olivine are also easily observed in hand specimens. From Volcan Ello, Sardinia and Roccamonfina similar rocks are obtained; they occur also in Bohemia, in Java, Celebes, Kilimanjaro (Africa) and near Trebizond in Asia Minor.
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A volcanic suite of Eocene age occurs in the Freemans Cove area of Bathurst Island. It is confined to the Southeast Bathurst Fault Zone, consisting of sills, dikes, agglomeratic vents and small plugs. Most of the suite consists of nephelinite or larnite-normative nephelinites and basanites, with rarer olivine melilite nephelinite, phonolite and tholeiitic and alkali basalt rocks. Extensive erosion has removed all traces of lava flows but lava fragments, bombs and scoria occur as clasts within the agglomerates.
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In: Walter Freudenberger, Klaus Schwerd (Red.): Erläuterungen zur Geologischen Karte von Bayern 1:500 000\. Bayerisches Geologisches Landesamt, Munich, 1996 (online ), p. 259-265 The western two-thirds of Franconia is dominated by the Triassic with its sandstones, siltstones and claystones (so-called siliciclastics) of the bunter sandstone; the limestones and marls of the Muschelkalk and the mixed, but predominantly siliciclastic, sedimentary rocks of the Keuper. In the Rhön, the Triassic rocks are overlain and intruded by volcanic rock (basalts, basanites, phonolites and trachytes) of the Tertiary.
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The Okete Volcanics erupted over short periods, between 1.8 and 3 Ma ago, from at least 27 tuff rings, or scoria mounds, surrounded by lava flows. At Maungatawhiri the initial eruption was of fine-grained volcanic tuffs, thought to be comminuted by water interacting with magma, followed by strombolian activity and lava flows. North of Papanui Point violent phreatomagmatic eruptions have formed tuff rings of airfall and pyroclastic surge deposits. The Okete Volcanics include basanites, alkali olivine basalts, hawaiites, and lavas with ultramafic xenoliths.
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Other igneous rocks such as phonotephrite are present in smaller quantities; these occur in the Satah Mountain volcanic field. Volcanic eruptions in the last 0.33 million years have been mainly basanitic and have occurred at the youngest eruptive centre, Nazko Cone. Basanites produced by these eruptions are significantly more undersaturated than basalts from older Anahim volcanoes in the west and may indicate an eastward shift toward a deeper or less depleted mantle source. It is also possible that as the North American Plate moves over the Anahim hotspot, it underlies thinner continental crust.
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Leucite lavas from which feldspar is absent are divided into the leucitites and leucite basalts. The latter contain olivine, the former do not. Pyroxene is the usual ferromagnesian mineral, and resembles that of the tephrites and basanites. Sanidine, melanite, hauyne and perovskite are frequent accessory minerals in these rocks, and many of them contain melilite in some quantity, The well-known leucitite of the Capo di Bove, near, Rome, is rich in this mineral, which forms irregular plates, yellow in the hand specimen, enclosing many small rounded crystals of leucite.
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Volcanic rocks dredged from Vesteris include basanite as the major component, phonotephrite and tephrite but also alkali basalt, mugearite and trachybasalt. Samples taken are porphyritic, rich in vesicles and contain phenocrysts of amphibole, clinopyroxene, kaersutite, olivine and plagioclase; these minerals also make up the groundmass of the rocks. These volcanic rocks define two separate geochemical suites, one formed by the basanites-tephrites and the other by the alkali basalts-mugearites. The formation of these two magma suites has been explained with fractional crystallization processes, mixing between different magmas and partial melting.
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Minor and major volcanoes of the Northern Cordilleran Volcanic Province, including the Queen Charlotte, Denali and Tintina fault zones A range of more heavily alkaline rock types not commonly found in the Western Cordillera are regionally widespread in the Northern Cordilleran Volcanic Province. These include nephelinite, basanite and peralkaline phonolite, trachyte, and comendite lavas. The most magnesium oxide-rich nephelinites, basanites and alkaline basalts all through the Northern Cordilleran Volcanic Province display trace element abundances and isotopic compositions that are logical with an asthenospheric source like those for average oceanic island basalt and for alkaline basalts younger than five million years in the rift-related Basin and Range Province of southwestern United States and northwestern Mexico. One hypothesized explanation for oceanic island basalt in the Earth's upper mantle under the Northern Cordilleran Volcanic Province is the existence of a slab window.
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