Continental collision

The collision between Gondwana and Laurasia to form Pangea occurred in a relatively brief interval, about 50 million years long.

The subduction zone runs along the edge of one of the continents and dips under it, raising volcanic mountain chains at some distance behind it, such as the Andes of South America today.

Oceanic crust is thin (~6 km thick) and dense (about 3.3 g/cm3), consisting of basalt, gabbro, and peridotite.

Because it contains thick continental crust, this lithosphere is less dense than the underlying asthenospheric mantle and normal subduction is disrupted.

Suture zones are often marked by fragments of the pre-existing oceanic crust and mantle rocks, known as ophiolites.

Examples of UHP terranes are known from the Dabie–Sulu belt of east-central China, the Western Alps, the Himalaya of India, the Kokchetav Massif of Kazakhstan, the Bohemian Massif of Europe, the North Qaidam of Northwestern China, the Western Gneiss Region of Norway, and Mali.

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

Crustal rocks are thrust faulted over the sediments and the mountain belt broadens as it rises in height.

A crustal root also develops, as required by isostasy; mountains can be high if underlain by thicker crust.

Another example is the collision of Arabia with Asia, which is squeezing the Anatolian sub-plate (present day Turkey).