Flexi Says: Plate boundaries are areas of active rock cycle processes. New igneous rock is formed from mantle upwelling along divergent plate boundaries. At convergent boundaries, old rock is subject to intense pressure where plates push together. This causes existing rock to transform into metamorphic rock. In a subduction zone where one plate sinks beneath the other, existing rock melts as the subducting slab becomes heated and subject to extreme pressure. The magma that forms rises upward through the crust and eventually either erupts or cools to form igneous rock. Large mountains that form along a convergent boundary will eventually be worn down into sediments. As wind and water carry the sediments downhill, they become deposited in thick layers and eventually will form new sedimentary rock.
