Flexi Says: An oceanic convergent plate boundary forms where two plates collide. In these collisions, one plate sinks beneath the other. A subduction zone forms along the boundary where the denser plate sinks into the mantle and is heated, causing plumes of molten magma to rise upward through the top plate. The features that form depend on the types of plates that meet. A volcanic island arc forms in an ocean-ocean plate convergence; a volcanic continental arc forms in an ocean-continent convergence.