Explain which type of melting (flux, decompression, heat transfer) is responsible for mafic magmas in each of the following plate-tectonic settings and why the resulting magma is mafic.

a) Mid ocean ridges

b) Continental drifts

c) Oceanic and continental volcanic arcs

d) Hot spots

a) Mid ocean ridges

Explanation:

The mid-oceanic ridges underling the hot asthenosphere which creates a depression that causes the melting of the peridotites at shallow depths. As they rise that results in mafic magma and this only takes place at divergent boundaries. Here the plates sperate and move away, causing magma below to rise and ill spaces of low pressure. The rocks then cool and new crust is firmed. The mafic rocks crystallize at higher temperatures and pressure.