Week 5 - continental crust against continental crust or oceanic crust against continental crust

During a family vacation, we had visited California, where an old oceanic crust inhabits the earth, the Andreas fault.

"The plate margins is where one plate is overriding another,which forces the other into the mantle beneath it. These boundaries are in the form of trench and island arc systems. All the old oceanic crust is going into these systems as new crust is formed at the spreading centers. Convergent boundaries also explain why crust older than the Cretaceous cannot be found in any ocean basin-- it has already been destroyed by the process of subduction. "

http://blogs.ei.columbia.edu/2016/02/22/how-does-continental-crust-form-scientists-have-a-new-bottom-up-theory/