Mariana Trench - Geology

Geology

The Mariana Trench is part of the Izu-Bonin-Mariana Arc convergent boundary system that forms the boundary between two tectonic plates. In this system, the western edge of one plate, the Pacific Plate, is subducted beneath the smaller Mariana Plate that lies to the west. Because the Pacific plate is the largest of all the tectonic plates on Earth, crustal material at its western edge has had a long time since formation (up to 170 million years) to compact and become very dense; hence its great height-difference relative to the higher-riding Mariana Plate, at the point where the Pacific Plate crust is subducted. This deep area is the Mariana Trench proper. The movement of these plates is also indirectly responsible for the formation of the Mariana Islands (which are caused by volcanism as a result of subduction of water trapped in minerals).