Geologic evolution of the Himalayan-Tibetan orogen

A review of the geologic history of the Himalayan-Tibetan orogen suggests t hat at least 1400 km of north-south shortening has been absorbed by the oro gen since the onset of the Indo-Asian collision at about 70 Ma. Significant crustal shortening, which leads to eventual construction of the Cenozoic T ibetan plateau, began more or less synchronously in the Eocene (50-40 Ma) i n the Tethyan Himalaya in the south, and in the Kunlun Shan and the Qilian Shan some 1000-1400 km in the north, The Paleozoic and Mesozoic tectonic hi stories in the Himalayan-Tibetan orogen exerted a strong control over the C enozoic strain history and strain distribution. The presence of widespread Triassic flysch complex in the Songpan-Ganzi-Hoh Xil and the Qiangtang terr anes can be spatially correlated with Cenozoic volcanism and thrusting in c entral Tibet. The marked difference in seismic properties of the crust and the upper mantle between southern and central Tibet is a manifestation of b oth Mesozoic and Cenozoic tectonics. The former, however, has played a deci sive role in localizing Tertiary contractional deformation, which in turn l eads to the release of free water into the upper mantle and the lower crust of central Tibet, causing partial melting in the mantle Lithosphere and th e crust.