when two tectonic plates collide the oceanic crust usually subducts beneath the continental crust because it is

When two tectonic plates collide, the oceanic crust usually subducts beneath the continental crust because it is denser and thinner than the continental crust. The oceanic crust is primarily composed of dense basalt and is about 6 km thick, while the continental crust is thicker (about 45 km) and made mostly of less dense granitic rocks. Due to this density difference, the denser oceanic crust bends and sinks beneath the lighter continental crust at a subduction zone during the collision of the two plates.