The Full Wiki

Convergent boundary: Map

  
  

Wikipedia article:

Map showing all locations mentioned on Wikipedia article:

In plate tectonics, a convergent boundary also known as a destructive plate boundary (because of subduction), is an actively deforming region where two (or more) tectonic plates or fragments of lithosphere move toward one another and collide. As a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near convergent boundaries.

When two plates move toward one another, they form either a subduction zone or a continental collision. This depends on the nature of the plates involved. In a subduction zone, the subducting plate, which is normally a plate with oceanic crust, 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 Himalayasmarker are formed.

Oceanic-continental
Continental-continental
Oceanic-oceanic


Convergent margins

A subduction zone is formed at a convergent plate boundary when one or both of the tectonic plates is composed of oceanic crust. The denser plate, made of oceanic crust, is subducted underneath the less dense plate, which can be either continental or oceanic crust. When both of the plates are made of oceanic crust, convergence is associated with island arcs such as the Solomon Islandsmarker.

An oceanic trench is found where the denser plate is subducted underneath the other plate. There is water in the rocks of the oceanic plate (because they are underwater), and as this plate moves further down into the subduction zone, much of the water contained in the plate is squeezed out when the plate begins to subduct. However, the recrystallization of ocean floor rocks, such as Serpentine, which are unstable in the upper mantle, recrystallize into Olivine, causing dehydration through loss of hydroxyl groups. This addition of water to the mantle causes partial melting of the mantle, generating magma, which then rises, and which normally results in volcanoes. This normally happens at a certain depth, about 70 to 80 miles below the Earth's surface, and so volcanoes are formed fairly close to, but not right next to, the trench.

Some convergent margins have zones of active seafloor spreading behind the island arc, known as back-arc basins.

When one plate is composed of oceanic lithosphere and the other is composed of continental lithosphere, the denser oceanic plate is subducted, often forming an orogenic belt and associated mountain range. This type of convergent boundary is similar to the Andes or the Cascade Range 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 most spectacular example of this is the Himalayasmarker.

When the subducting plate approaches the trench obliquely, the convergent plate boundary includes a major component of strike-slip faulting. The best example of this is the Sumatramarker convergent margin, where convergent action is occurring intermixed with a strike-slip boundary.

Examples



Other types of plate boundaries



See also



External links




Embed code:






Got something to say? Make a comment.
Your name
Your email address
Message