What is a subduction zone?

1 Answer

It is a location on the earth surface where an ocean plate is pushed under another plate either oceanic or continental.


The plates are theorized to move via convection currents and the relatively new theory of slab pull.

Slab pull is now thought to be the main driver of the movement of plates in subduction. Convection currents, are rising semi-liquid material warmed by the nuclear processes in the core, they're thought to contribute to plate movement.
Where hot, rising semi-liquid mantle, reaches the crust, there are often mid-ocean ridges and rift valleys, where new crust is formed. There are also locations where the cooler liquid in the mantle sinks down.

Usually where the mantle sinks, the crust is subducted down under the weight of a less dense plate and it's own weight.
When this plate (usually oceanic) made of basalt meets a less dense plate (usually continental) made of granite it is subducted below it, due to its much greater density and is helped by the movement of the mantle below it.
As it is melting in the mantle, it can form smaller convection currents, that help pull it down, this is the subduction zone.

The area where the two plates meet and the oceanic plate is subducted, is known as the subduction zone.

A classic example of a subduction zone is found off the coast of South America. Part of the Pacific Ocean plate is pushed under the Continental plate of South America. Deep ocean trenches can be found off the coast, where the plate goes down, and where the continental plate rises, is the formation of the Andes.
Volcanoes most often occur where the magma escapes up through the continental crust, as more of the oceanic crust is melted down to form new mantle.
There is also the increase of dangerous earthquakes, as the plates become stuck and sea water leads to more violent releases of energy.