Final answer:
Oceanic crust melts into magma at subduction zones due to the combination of high pressure and temperature and flux melting caused by water released from hydrated minerals. This leads to the formation of magma and potential volcanic activity. Mantle convection drives plate tectonics, balancing crust creation and destruction.
Step-by-step explanation:
Why Does Subducting Oceanic Crust Melt into Magma?
Subduction zones are areas where two tectonic plates come together, and one, usually the oceanic crust, is forced beneath the other. When this denser oceanic plate is subducted, it encounters high temperature and pressure conditions several hundred kilometers below Earth’s surface, leading to its melting. Water from hydrated minerals within the subducting plate is released, which then lowers the melting temperature of the overlying mantle, causing magma to form. This process is known as flux melting and contributes to the creation of new magma that can lead to volcanic activity.
Plate tectonics are driven by mantle convection, which is the movement of warmer and cooler material within the Earth’s mantle. This circulation of material can cause both the creation of new crust at rift zones and the destruction of old crust at subduction zones, maintaining a balance in Earth’s crust. The subducted material contributes to a downward-flowing convection current, which recycles Earth's lithosphere in a continuous cycle.