The answer is ‘convergent plate margins’. This occurs at subduction zones (When continental and oceanic plates collide, thus the thinner and more dense oceanic plate is overridden by the thicker and less dense continental plate). As the oceanic plate descends, it is forced into higher temperature environments and begin to melt. Buoyant magma chambers above the subducting oceanic plate and slowly ascends through the overlying materials, melting and fracturing their way upwards.