This process causes the oceanic crust to return to the mantle were it is re-melted into magma . The process also causes the movement of continental crust across the surface of the Earth. Beneath the rift zone upwellings of magma occur in the mantle . These upwellings produce fissures and volcanoes on the ocean surface. The added rock, produced from the solidification of magma, pushes previously formed oceanic crust horizontally away from the rift zone like a conveyor belt.
Ocean crust is returned to the mantle through subduction .
This can occur when ocean crust meets continental crust or other ocean plates.