Andesites in island arcs and continental margins: Relationship to crustal evolution

Andesites of both island arc and continental margin environments contain petrologic evidence of mixing of mantle and crustal melts. Andesitic volcanism appears to involve addition of mantle-derived basaltic magma to the crust and fractionation of preexisting crustal material. Changes in andesitic volcanism with increasingly continental character of the crust reflect changes in a rhyolitic component derived from increasingly aged and fractionated crust. The initial stage in development of continental crust is partial melting of oceanic crust.