Arcmagmatism

Arcmagmatism is a proposed geological concept that describes a specific type of magmatic activity that occurs in arc settings. These arcs, such as volcanic island arcs or continental volcanic arcs, are characterized by the subduction of one tectonic plate beneath another. Arcmagmatism specifically refers to the generation and ascent of magma from the mantle wedge, the region of the upper mantle situated above the subducting slab.

The process is thought to be initiated by the release of water and other volatiles from the descending oceanic crust as it is heated and subjected to increasing pressure. These volatiles rise into the overlying mantle wedge, lowering its melting point and causing it to melt. This partial melting generates basaltic magma, which is typically less dense than the surrounding mantle and begins to ascend. As this magma rises through the overriding plate, it can undergo further differentiation through fractional crystallization and assimilation of the crustal rocks it encounters, leading to a more diverse range of magma compositions, including andesitic and rhyolitic. The surface expression of this process is the formation of volcanic arcs.