Pliocene tectonics and lithofacies paleogeography of the Tibetan Plateau

Based on the data obtained from 1:250 000 geological mapping conducted by China Geological Survey in 1996-2008 and available data concerning the Pliocene strata,the authors recognized 95 remnant basins in the Tibetan Plateau and its adjacent areas.In this study,the Pliocene tectonic evolution and lithofacies paleogeography of Tibetan Plateau has been discussed.The continuous collision between the Indian plate and the Eurasian plate along the Brahmaputra suture zone controlled the overall tectonic geomorphology of the Tibetan Plateau in the Pliocene and extensively affected the tectonic uplift.The Kunlun Mountains and Qilian Mountain to the northeast were two tectonic uplift erosion source areas,which sandwiched the Qaidam basin from the south and the north respectively. The Qaidam basin is the largest interior basin in northeastern Tibetan Plateau.The northern and eastern areas of the Qilian Mountain were characterized by the alternate range-basin pattern,which received denudation materials from surrounding mountains.Further strong uplift in the late Pliocene(called Episode A of the Qinghai-Tibet Movement) changed these intermontane basins into erosional regions.The Tarim basin in Xinjiang and Qiangtang and Hoh Xil in northern Tibet constituted an extensive tectonic sag basin-blunt flood plain deposition region.Southeastern Tibet was composed mainly of pull-apart basins caused by a series of strike-slip faults, which accumulated flood alluvial conglomerates in the early Pliocene and lacustrine and delta deposits in the middle Pliocene.Flood alluvial conglomerates were deposited again in the late Pliocene due to the further uplift of the mountains.Some nearly NS-trending rift basins were developed in the southern part of the Tibetan Plateau in response to a certain degree of plateau collapse.Sedimentary facies of these basins were divided into three stages from early to late Pliocene,similar to those of southeastern Tibetan Plateau.The Ganges area deposited coarse clastic sediments due to the Pliocene rapid uplift of the Himalaya and formed long and narrow Siwalik Group.The general topography of the Tibetan Plateau in the Pliocene inherited the Miocene topography but was higher in the east and the south and lower in the east and the north,with the height difference obviously increasing relative to the Miocene.