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Alkaline magmas are characteristic of continental rifting, areas overlying deeply subducted plates, or at intraplate hotspots. [2]: Ch6 They are more likely to be generated at greater depths in the mantle than subalkaline magmas. [2]: Ch23.6. Alkaline rocks are rare in the Archean, but become common in the Proterozoic.
The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. 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 ...
The Sunda Arc is a volcanic arc that produced the volcanoes that form the topographic spine of the islands of Sumatra, Nusa Tenggara, Java, the Sunda Strait, and the Lesser Sunda Islands. The Sunda Arc begins at Sumatra and ends at Flores, and is adjacent to the Banda Arc. [1] The Sunda Arc is formed via the subduction of the Indo-Australian ...
Magma consists of liquid rock that usually contains suspended solid crystals. [14] As magma approaches the surface and the overburden pressure drops, dissolved gases bubble out of the liquid, so that magma near the surface consists of materials in solid, liquid, and gas phases.
Volcanic arcs are characterized by explosive eruption of calc-alkaline magma, though young arcs sometimes erupt tholeiitic magma [7] and a few arcs erupt alkaline magma. [8] Calc-alkaline magma can be distinguished from tholeiitic magma, typical of mid-ocean ridges, by its higher aluminium and lower iron content [9]: 143–146 and by its high ...
The tholeiitic magma series (/ ˌθoʊliˈaɪtɪk /) is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma into a more evolved, silica rich end member. Rock types of the tholeiitic ...
This has been interpreted as fresh magma injected into the magma chamber that may have helped trigger the eruption. [11] Eruption of basanite and other alkaline magmas characterizes the late alkaline phase (rejuvenation phase) [12] of volcanic islands, which often comes 3 to 5 million years after the main shield-building phase. [13]
Trachyandesite is an extrusive igneous rock with a composition between trachyte and andesite. It has little or no free quartz, but is dominated by sodic plagioclase and alkali feldspar. It is formed from the cooling of lava enriched in alkali metals and with an intermediate content of silica. [1][2]