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.
Plate thickness also varies greatly, ranging from less than 15 km for young
oceanic lithosphere to about 200 km or more for ancient continental lithosphere
(for example, the interior parts of North and South America).