Adakites are intermediate to felsic volcanic rocks that have geochemical characteristics of magma that have partially melted from the altered basalt that is subducted below volcanic arcs. Most magmas derived in subduction zones come from the mantle above the subducting plate when hydrous fluids are released from minerals that break down in the metamorphosed basalt, rise into the mantle, and initiate partial melting. However, Defant and Drummond recognized that when young oceanic crust is subducted, adakites are typically produced in the arc. They postulated that when young oceanic crust is subducted it is "warmer" than crust that is typically subducted. The warmer crust enables melting of the metamorphosed subducted basalt rather than the mantle above. Experimental work by several researchers has verified the geochemical characteristics of "slab melts" and the contention that melts can form from young and therefore warmer crust in subduction zones. The geochemical characteristics Defant and Drummond gave for adakites are: ⁕SiO2 greater than 56 wt % ⁕Al2O3 greater than or equal to 15 wt % ⁕MgO normally less than 3 wt %8786 Wikipedia [ - ]

Adakites are intermediate to felsic volcanic rocks that have geochemical characteristics of... [ + ]