Where it All Comes Together

  Are the result of two plates moving toward one another, in other words they collide.  The specific processes and features formed during the collision depend on the types of crust involved in the collision  Since lithospheric material is generally destroyed during convergence these plate boundaries are also referred to as destructive plate boundaries. Convergent Plate Boundaries

  There are three types of convergent plate boundaries, depending on the crustal material in contact at the collision zone  Oceanic-continental convergence  Oceanic-oceanic convergence  Continental-continental convergence

  Because oceanic plates are more dense than continental crust, therefore when they collide the less dense continental material override the oceanic plate which is thrust under the continental plate.  This process is called subduction.  The resultant subduction zone is a long narrow zone where a lithospheric plate is sinking into the asthenosphere. Ocean-Continental Convergence

  The site of subduction is marked by a deep sea trench where the subducting oceanic plate bends.

  They may be thousands of kilometres long,  km deep  And about 100 km wide Deep Sea Trenches The Mariana Trench is the deepest part of the world's oceans, and the lowest elevation of the surface of the Earth's crust. It reaches a maximum-known depth of about kilometres It reaches a maximum- known depth of about kilometres The trench is about 2,550 kilometres long but has a mean width of only 69 kilometres. If Mount Everest, the highest mountain on Earth at 8,848 metres, were set in the deepest part of the Mariana Trench, there would be 2,076 metres of water left above it.

  Associated with subduction zones are earthquakes or seismic activity.  The region of earthquake activity is referred to as the Benioff zone.  As the subducting plate descends into the asthenosphere it is heated.  The resulting magma may solidify to form intrusive igneous rocks or it may upwell (as the magma is less dense than the surrounding rock) to form volcanoes on the overriding plate Benioff Zone

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  The volcanoes that form on the continental plate are aligned parallel to the subduction zone.  This arrangement of volcanoes is termed a volcanic arc.  An example of the an oceanic-continental convergence zone is the Andes Mountain Range

  Where two oceanic lithospheric plates meet and collide, the older plate, which will be thicker and denser will be subducted.  These two plates colliding will also create a subduction zone.  Its features are similar to that of the oceanic- continental convergence. Oceanic-Oceanic Convergence

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  A difference with oceanic-oceanic convergence is that volcanoes form on the ocean floor.  These volcanoes may breach the sea level to form islands.  The linear arrangement of the islands is termed an island arc.  An example of an island arc are the Aleutian Islands

  Since both plates are of the same density neither can subduct under the other.  This leads to the plates being fused and compressed into a single continental block.  Earthquake and seismic activity is common. Continental-Continental Convergence

  An example of continental – continental convergence is the Himalayan mountains, where India has collided with Asia Everest & Lotus K2