Plaque des Mariannes

The Mariana Plate is a micro tectonic plate located west of the Mariana Trench which forms the basement of the Mariana Islands which form part of the Izu–Bonin–Mariana Arc. It is separated from the Philippine Sea Plate to the west by a divergent boundary with numerous transform fault offsets. The boundary between the Mariana and the Pacific Plate to the east is a subduction zone with the Pacific Plate subducting beneath the Mariana. This eastern subduction is divided into the Mariana Trench, which forms the southeastern boundary, and the Izu–Ogasawara Trench the northeastern boundary. The subduction plate motion is responsible for the shape of the Mariana plate and back arc. Subduction at the Mariana plate has been going on for over 50 million years. Some theories of the origin of this microplate is that when the Pacific plate began to subduct beneath the Philippine plate the volcanism and spreading ridge started to make an arc. This geological activity caused the section of the Philippine plate to break off and become the Mariana microplate. The Mariana Islands consist of volcanoes that are active and dormant and are made up of volcanic and sedimentary rocks from the Pleistocene. As the Pacific Plate subducts beneath the Mariana Plate, it creates a trench. This is the Mariana Trench, and it is the deepest trench in the world. Another result of this subduction is the Mariana Islands. These are formed from dehydration of the subducting, old oceanic crust creates melt, and the melt rises to the surface through a volcano. This volcanism has been occurring for almost 50 million years. The rock type in the area is volcaniclastic sediments on top of igneous rocks. The source of these rocks are from crustal spreading. Just off the eastern coast of Mariana there are big seamounts made of serpentinized periodic. They are formed from mud volcanism. The composition for the seamounts differs in the Izu–Ogasawara Trench and Mariana systems which indicate regional changes in geology.