What is the difference between Oceanic and Continental Crust? What happens to the Oceanic crust when they collide?
Both oceanic and continental crust are less dense than the underlying mantle rocks which are ~3.3g/m3 and therefore they 'float' on top of the mantle. Oceanic crust is formed primarily of dense basaltic rock (~2.8g/m3). This crust is relatively thin, ~7km thick whereas the less dense (~2.7g/m3), granitic continental crust is thicker, ~30-40km. The differences in density and thickness of the two crusts mean that, due to isostasy, the continental crust sits higher at the earths surface than the ocean crust, hence continents are found above sea level.These crusts can collide with one another in an Oceanic-Continental convergence boundary. Here the two plates are moving towards one another and the denser Oceanic crust is subducted beneath the Continental crust.
