COLLISION OF THE INDIAN PLATE AND EURASIAN PLATE AND UPLIFT OF THE TIBETAN PLATEAU

The Tibetan plateau is underlain by at least three continental fragments, the Kunlun, Qiangtang and Lhasa terranes, succesively accreted to the southern margin of Asia during early and middle Mesozic time（Allegre, 1984）, and the collision of these fragments with Asia surely did not lead to localized crustal thickening. The mountains that formed at those times, however, must have been eroded away when marine limestones were deposited in much of southern and wetern Tibet in Late Cretaceous time（Chang et al, 1986）. Therefore these areas were below sea level, and the crust beneath them would not have been thick. Now. the Tibetan plateau, with a height ot of above 4,500 to 5,000 m, is one of the Earth’s most extraodinary topographic features.The crustal thickening is surely a consequence of the collision and subsequent penetration of India into the rest of Asia in Cenozoic time. As we know, the closing of the South Tethys Sea and final convergence of the Indian plate with the Enrasian plate occurred at 54-50 Ma ago（Molnar and Tapponnier, 1975）. By the time of collision the land formed by the comlination of the Indian platc and Eurasian plate wass estimated to be less than 1,000m above sea level and the crustal thickness was not over 40 km. In the Neogene（23-20 Ma）, the Tibetan plateau and the Mid-Asia mountains began to uplift simultaneously. So the history of sedimentation and uplift of the Tibetan plateau may have continued from the early Tertiary to the Recent. It is believecl that the uplift of the plateau did notled to the collision of the Indian plate and the Eurasian plate.