What happens to the plates and the mantle at plate boundaries?

The plate boundaries are the locations where the plates shares either a divergent, transform or convergent type of boundaries. The convection current that is generated in the mantle region of the earth's interior led to the breakdown of the lithosphere into various large and small plates.

At the divergent plate boundaries, the magma rises upward from the interior of the earth, causing upwelling of the mantle, and thereby adding new materials to the crust along the mid-oceanic ridge.

At the convergent plate boundaries, the plates collides and denser one sinks to the interior of the earth, causing the mantle to shrink.

At the transform plate boundaries, the plates are conserved and the mantle remains unchanged.