Where it All Comes Together. Are the result of two plates moving toward one another, in other...

Convergent Plate Boundaries

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, 8-11+ 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 11.03 kilometres It reaches a maximum-known depth of about 11.03 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

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

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