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QAPF diagram with basalt/andesite field highlighted in yellow. Andesite is distinguished from basalt by SiO 2 > 52%. Andesite is field O2 in the TAS classification.. Andesite is an aphanitic (fine-grained) to porphyritic (coarse-grained) igneous rock that is intermediate in its content of silica and low in alkali metals.
For example, andesitic magmatism is associated with the formation of island arcs at convergent plate boundaries while basaltic magmatism is found at mid-ocean ridges during sea-floor spreading at divergent plate boundaries. On Earth, magma forms by partial melting of silicate rocks either in the mantle, continental or oceanic crust. Evidence ...
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.
Composite or stratovolcanoes often have andesitic magma and typically form the extrusive rock andesite. Andesitic magma is composed of many gases and melted mantle rocks. [2] Cinder or scoria cones violently expel lava with high gas content, [2] and due to the vapor bubbles in this mafic lava, the extrusive basalt scoria is formed. [6]
When rock melts, the liquid is a primary magma. Primary magmas have not undergone any differentiation and represent the starting composition of a magma. [96] In practice, it is difficult to unambiguously identify primary magmas, [97] though it has been suggested that boninite is a variety of andesite crystallized from a primary magma. [98]
Before the eruption, Aniakchak was a 2,300 meters (7,500 ft) high [121] deeply eroded stratovolcano [122] with two separate magma bodies, one andesitic and the other rhyodacitic, under Aniakchak at least 4.1–5.5 kilometers (2.5–3.4 mi) in depth. [64] These two magma bodies had evolved independently in the time before the eruption. [123]
The composition of the soil found on Vikram’s landing site is consistent with an ancient magma ocean, the authors conclude. When analyzing the soil, the researchers found a relatively uniform ...
[1] [2] It is typically dark in color (brown, black or purplish-red), and basaltic or andesitic in composition. Scoria has relatively low density , as it is riddled with macroscopic ellipsoidal vesicles (gas bubbles), but in contrast to pumice , scoria always has a specific gravity greater than 1 and sinks in water.