A tectonic plate (also called lithospheric plate) is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. Plate size can vary greatly, from a few hundred to thousands of kilometers across; the Pacific and Antarctic Plates are among the largest. At convergent plate boundaries, sedimentary rock from the ocean floor gets pushed down into the mantle. The crust increases in temperature as it dives deeper into the mantle. Eventually, the crust melts and rises to the surface causing a volcanic eruption, creating igneous rocks.