Convergent boundary

A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Wadati–Benioff zone.[1] These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.

Simplified diagram of a convergent boundary

Plate tectonics is driven by convection cells in the mantle. Convection cells are the result of heat generated by the radioactive decay of elements in the mantle escaping to the surface and the return of cool materials from the surface to the mantle.[2] These convection cells bring hot mantle material to the surface along spreading centers creating new crust. As this new crust is pushed away from the spreading center by the formation of newer crust, it cools, thins, and becomes denser. Subduction begins when this dense crust converges with less dense crust. The force of gravity helps drive the subducting slab into the mantle.[3] As the relatively cool subducting slab sinks deeper into the mantle, it is heated, causing hydrous minerals to break down. This releases water into the hotter asthenosphere, which leads to partial melting of asthenosphere and volcanism. Both dehydration and partial melting occurs along the 1,000 °C (1,830 °F) isotherm, generally at depths of 65 to 130 km (40 to 81 mi).[4][5]

Some lithospheric plates consist of both continental and oceanic lithosphere. In some instances, initial convergence with another plate will destroy oceanic lithosphere, leading to convergence of two continental plates. Neither continental plate will subduct. It is likely that the plate may break along the boundary of continental and oceanic crust. Seismic tomography reveals pieces of lithosphere that have broken off during convergence.

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