Convergent boundary
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In plate tectonics, a convergent boundary – also known as a convergent plate boundary, active margin, compression boundary or a destructive boundary – is a region of the Earth's crust where two tectonic plates are in motion toward one another.
The motion of two plates toward one another forms either a subduction zone or a continental collision. This depends on the nature of the plates involved.
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[edit] Convergent margins
A subduction zone forms at a convergent plate boundary when one or both of the tectonic plates is composed of oceanic crust. The less dense plate usually rides over the denser plate, which is subducted. This type of plate convergence is associated with island arcs such as the Solomon Islands. The island arc is formed above the subduction zone within the over-riding plate, with a deep oceanic trench formed by warping of the crust.
Some convergent margins have zones of active seafloor spreading, known as back-arc basins.
When one plate is composed of oceanic crust and the other is composed of continental crust, the oceanic plate is subducted, forming an orogenic belt and associated mountain range, often with an oceanic trench offshore. This type of convergent boundary is similar to the Andes or the Cascade Ranges in North America.
When two plates containing continental crust collide, both are too light to subduct. In this case, a continent-continent collision occurs, creating especially large mountain ranges. The typical example of this is the Himalayas.
Occasionally plate convergent boundaries are involved with complex faulting and can form transform plate boundaries, where some component of strike-slip faulting is involved at a zig-zag section of the plate boundary. The best example of this is the New Zealand convergent margin, where convergent action is occurring intermixed with a strike-slip boundary.
[edit] Examples
- the collision between the Eurasian Plate and the Indian Plate which is forming the Himalayas.
- the collision between the northern part of the Pacific Plate and the NW North American Plate which is forming the Aleutian Islands.
- the collision between the Nazca Plate and the South American Plate which has formed Andes Mountains.
- the collision between the Pacific Plate and the Australian Plate, forming the New Zealand transform boundary.
