Oceanic-Oceanic Convergence
When two oceanic plates meet, one plate sinks below the other. As with the convergence of oceanic and continental plates, trenches are formed at the subduction zone. Challenger deep, the deepest part of the oceans is part of the Marina Trench in the subduction zone between the Pacific and Philippine Plates. Challenger Deep is so deep that even Mount Everest could not fill in and that's what Oceanic-Oceanic Convergence.