Continental collision zones

Continental collision zones occur when two plates containing large areas of continental crust are pushed together. As the continental areas converge, the oceanic crust between them is consumed by subduction until the continental areas collide. The results of such a collision can be seen in the Himalayas which formed through the collision of India with Asia about 10 Ma ago (shown on the diagram on the right).
The Alps and Atlas mountains also formed in this way, by the collision of the African and European plates about 60 Ma ago. Although the collision between Asia and India occurred about 45 Ma ago, the area is still not stable. Re-adjustments are still occurring, and this is still causing shallow earthquakes in the Himalayan region.
An episode of mountain building such as this is known as an orogeny. During these events, large belts of fold mountains are generated as large quantities of sediment are scraped off the subducting ocean plate and accumulate in the shrinking ocean basin. When the two continents finally converge, the sediments are compressed and deformed into linear belts of fold mountains. During this compression, the rocks are subjected to the intense pressures and temperatures of regional metamorphism which bakes the rocks and causes them to change into much harder, denser rocks composed of different minerals to the original sediment.

Collision of continental masses causes crustal thickening, and the intense pressure and temperatures which are present in the core of the collision zone causes the rocks to melt and produce bodies (diapirs) of silica-rich magma. Partial melting of continental material generates a granitic magma, which rises and solidifies to produce granitic batholiths in the core of the fold mountains. In the early stages of melting, some of the magma may reach the surface and erupt as magma from volcanoes. Usually this volcanic activity dies out as the collision zones become more established.


Find out more about plate tectonics:

Plate tectonics make the world go round: introduction
Constructive margins: Continental (rift valleys)
Oceanic (mid-ocean ridges)
Destructive margins: Continental collision
Ocean-continent destructive margins
Ocean-ocean destructive margins (island arcs)
Conservative margins
Continental drift
Plume and hotspots
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February 2007