Why did the oceanic Crust subducted

Answer mauritania is in the northwestern part of african, meaning its in the western hemisphere, and how do i know/ the map showed me so; ///: )

Can you show the map?

Magma forms by partial melting of upper mantle and crust. partial melt means that only a fraction of the available material forms a melt, and that the remainder stays solid. the partial melt rises because of its lower density and ascends through he crust. this is so conclusive mean the answer would be magma igneous rocks or balistic magma.