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If the subducted oceanic crust is basaltic, why is the composition of magma felsic?

If the subducted oceanic crust is basaltic, why is the composition of magma felsic?

naxiv

During convergent collisions with the oceanic crust and continental crust. The magma produced when the subducted plate rises is felsic? Why

Reply 1

Surtr

Because the magma does not come from the subducted plate. Water is released from the subducting plate which lowers the melting temperature of the mantle wedge above the subducting plate. This triggers melting, and those melts are basaltic. As those melts rise through the crust they are fractionated or assimilate crystal material. Because felsic magmas have a lower density than magic magmas they rise farther up in the crust so the volcanism you observe is felsic.

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