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Geology of the Tibetan Plateau

The Tibetan Plateau has been built up by a number of colliding continental fragments. Paleomagnetic data shows that the fragments came from southern latitudes during the Paleozoic era and moved north, stacking up against each other during the Paleozoic and subsequent Mesozoic era. There are four main crustal blocks underlying the Tibetan plateau. These are, from north to south, the Kunlun, Songban-Ganzi, Qiangtang, and Lhasa terranes. With the exception of the Songban-Ganzi Complex, these are all continental fragments, underlain with Precambrian basement. It is thought that the uplift of the plateau brought it to its present height at 8 Million years ago from beginnings in the early Miocene. Under the plateau the thickness of the Earth's crust is approximately 65 kilometres (40 mi), which compares to a more usual thickness of 30 kilometres (19 mi) found elsewhere. The unusual thickness of the crust found here could be explained by one of three theories: continental subduction, distributed shortening or lower crustal flow.

Research published in 2008 showed that uplift did not occur across the entire plateau at the same time, but happened in a number of stages. The central plateau experienced a raise in height much earlier than the north and south (now the Himalayan mountains) areas.

http://oak.ucc.nau.edu/wittke/Tibet/Plateau.html http://www.geo.arizona.edu/~ozacar/frontp~1.htm