Continental collision

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In

sutured together. Continental collision is only known to occur on Earth.

Continental collision is not an instantaneous event, but may take several tens of millions of years before the

occurred in a relatively brief interval, about 50 million years long.

Subduction zone: the collision site

The process begins as two

.

Deep subduction of continental crust

The

. The fact that most UHP terranes consist of thin sheets suggests that much thicker, volumetrically dominant tracts of continental crust are more deeply subducted.

Orogeny and collapse

An

. Crustal thickening provides one of two negative feedbacks on mountain growth in collision zones, the other being erosion. The popular notion that erosion is responsible for destroying mountains is only half correct - viscous flow of weak lower mantle also reduces relief with time, especially once the collision is complete and the two continents are completely sutured. Convergence between the continents continues because the crust is still being pulled down by oceanic lithosphere sinking in the subduction zone to either side of the collision as well as beneath the impinging continent.

The pace of mountain building associated with the collision is measured by

.

Far-field effects

The effects of the collision are felt far beyond the immediate site of collision and mountain-building. As convergence between the two continents continues, the region of crustal thickening and elevation will become broader. If there is an oceanic free face, the adjacent crustal blocks may move towards it. As an example of this, the collision of India with Asia forced large regions of crust to move south to form modern

, the deepest lake on Earth.

Fossil collision zones

Continental collisions are a critical part of the supercontinent cycle and have happened many times in the past. Ancient collision zones are deeply eroded but may still be recognized because these mark sites of intense deformation, metamorphism, and plutonic activity that separate tracts of continental crust having different geologic histories prior to the collision. Old collision zones are commonly called "suture zones" by geologists, because this is where two previous continents are joined or sutured together.

References

• Ernst, W.G. (2006). "Preservation/exhumation of ultrahigh-pressure subduction complexes".
  doi:10.1016/j.lithos.2006.03.049
  .
• Ernst, W.G.; Maruyama, S. Wallis; Wallis, S. (1997). "Buoyancy-driven, rapid exhumation of ultrahigh-pressure metamorphosed continental crust". Proceedings of the National Academy of Sciences. 94 (18): 9532–9537.
  PMID 11038569
  .
• O'Brien, P.J. (2001). "Subduction followed by collision; Alpine and Himalayan examples". Physics of the Earth and Planetary Interiors. 127 (1–4): 277–291.
  doi:10.1016/S0031-9201(01)00232-1
  .
• Toussaint, G.; Burov, E.; Avouac, J.-P. (2004). "Tectonic evolution of a continental collision zone: A thermomechanical numerical model" (PDF). Tectonics. 23 (6): TC6003.
  S2CID 18607619
  .
• Song, S.G. (2014). "Continental orogenesis from ocean subduction, continent collision/subduction, to orogen collapse, and orogen recycling: The example of the North Qaidam UHPM belt, NW China". Earth-Science Reviews. 129 (3–4): 59–84.
  doi:10.1016/j.earscirev.2013.11.010
  .

External links

• Where Continents Collide
• Dynamics of Continental Collision Zones
• The Wilson Cycle