The process involved in plate tectonics is similar to a Hadley cell in climatology.
Hot magma rises to the surface at a rift zone and creates new crust.
The crust spreads away from this zone. At subduction zones, the crust moves down into the earth, where it can be recycled in a loop. At subduction zones, the crust can be melted ad rise to form volcanoes along this zone such as the Ring of Fire around the Pacific Ocean. Also, material that is on the surface of the crust that is suducted can be attached to the other continent as a terrane. It is possible that much of the west coast of North America is comprised of terranes attached like this.