what drives the process of plate tectonics
What drives the process of plate tectonics. Tectonic plates are pieces of the Earth's crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km thick and consist of two principal types of material: oceanic crust and continental crust. The composition of the two types of crust differs markedly, with basaltic rocks dominating oceanic crust, while continental crust consists principally of lower density granitic rocks.