Cenozoic Uplift And Growth Of Northwestern Margin Of The Tibetan Plateau

The Tibetan Plateau is the focus of international geoscientists. The long-distance effect of India-Eurasia collision on the northern plateau has been emphasized recently. The northern boundary of the Tibetan plateau, constituting of a series of faults including the Northern Qilian and the West Kunlun thrust system, is an important adjuster of ongoing plate convergence between India and Eurasia. Locating near the Pamir structural knot, the research on uplift and denudation of the West Kunlun is of fundamental significance for investigating uplift of the Tibetan plateau.Basing on previous research, Cenozoic sediments along the northern West Kunlun and in the Mazar Tag have been studied here on paleomagnetic feature, structural geomorphology, satellite image, detrital zircon provenance and seismic data. The deformation and sedimentary features were employed to discuss the tectonic uplift process and paleoenvironment change.The eastward spreading of Cenozoic tectonic activity can be supported by all following evidences: the molasse is thicker in the west than the east, volcanic and metamorphic rocks occur in the east firstly; anti-clockwise paleocurrent directions from Wuqia to Xiyu formation indicated by AMS; the identical eastward bend of various rivers, the anisomerous terraces developed from west to east and the west-to-east provenance transition of zircons in Miocene conglomerate collected from Mazar Tag.According to the features of fold in Miocene strata and deformation in quaternary lacustrine sediments, the faults in Mazar Tag are mainly northward thrust, as the front of the northern West Kunlun thrust. After developed the anticline where the Kekeya gas-field occur, the fault might further extend to the north. Defined by quaternary strata, the thrust in Mazar Tag was considered to be started in Pleistocene or Holocene, implying that the northward fault from the piedmont of West Kunlun Mountain continued to the late Quaternary period and might keep active presently. The orange incompact sandstone occurred in Miocene strata developed in Mazar Tag might be Aeolian and formed no late than 5.3Ma, suggesting the possible latest formation of the Taklimakan Desert. The pattern that fluvial sediments interlaid with Aeolian demonstrated the evolvement between river and desert. The reason why coarse sediments occurred in Mazar Tag is less than piedmont of West Kunlun is the closer to the desert.Then the conclusion can be summarized as follows: the growth of the Tibetan Plateau in different parts is not synchronous, as the western structural knot of the India-Eurasia collision, Pamir underwent intense tectonic movement. The frontal West Kunlun thrust made the mountain uplift firstly in the west segment and then spread to the east. Intense denudation accompanied with the rapid rise developed huge piedmont sediments; the rapidly uplifted height of the West Kunlun Mountain in late Cenozoic could have modified atmospheric circulation patterns, partially accounting for the arid climate in the Tarim Basin, and developed the aeolian interlaid with the fluvial sediments. The end of the frontal thrust from West Kunlun to Tarim Basin might have expanded to the hinterland and enhanced the ancient faults. In Mazar Tagh, the activity extended into the present and made the significant deformation in Quaternary lacustrine sediments.