Convergent boundaries

In plate tectonics, a convergent boundary, also known as a destructive plate boundary, is a region of active deformation where two or more tectonic plates or fragments of the lithosphere are near the end of their life cycle. This is in contrast to a constructive plate boundary (also known as a mid-ocean ridge or spreading center). As a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near destructive boundaries, where subduction zones or an area of continental collision (depending on the nature of the plates involved) occurs. The subducting plate in a subduction zone is normally oceanic crust, and moves beneath the other plate, which can be made of either oceanic or continental crust. During collisions between two continental plates, large mountain ranges, such as the Himalayas are formed. In other regions, a divergent boundary or transform faults may be present.

The reason for the existence of convergent boundaries are the mid-ocean ridges that were only beginning to be understood with the acceptance of the theory of plate tectonics in the mid-1960s. The radioactive decay of elements within the rocks in the interior of the earth generates large amounts of heat that moves magma to the surface of the crust in a process called mantle convection. This results in new oceanic crust or sea floor being formed that slowly moves away from the ridges (sometimes called spreading centers) towards the subduction zones. In other words, new sea floor originates from the upwelling rock as it emerges from the depths of the mantle and it slowly cools as it is transported over the millennia to the collision or subduction zones where it is consumed or recycled.

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