Tectonics of the Xining Basin in NW China and its implications for the evolution of the NE Qinghai-Tibetan Plateau

The continuous Cenozoic strata in the Xining Basin record the growth and evolution of the northeastern Qinghai-Tibetan Plateau. Here, the mechanisms and evolution of the Xining Basin during the Cenozoic were investigated by studying the sedimentary facies of 22 Cenozoic sections across the basin and detrital zircon U-Pb ages of three Cenozoic sections located in the eastern, central and western basin, respectively. In the Eocene (ca. 50-44Ma), the India-Eurasia Collision affected the northeastern Qinghai-Tibetan Plateau. The Central Qilian Block rotated clockwise by ca. 24 degrees to form the Xining Basin. The Triassic flysch sediments surrounding the basin were the primary sources of sediment. Between ca. 44-40Ma, the basin enlarged and deepened, and sedimentation was dominated by saline lake sediments. Between ca. 40-25.5Ma, the Xining Basin began to shrink and dry, resulting in the deposition of saline pan and saline mudflat sediments in the basin. After ca. 20Ma, the Laji Shan to the south of the Xining Basin was uplifted due to the northward compression of the Guide Basin to the south. Clasts that eroded from this range dominated the sediments as the basin evolved from a lacustrine environment into a fluvial system. The Xining Basin was an extensional basin in the Early Cenozoic, but changed into a compressive one during the Late Cenozoic, it was not a foreland basin either to the Kunlun Shan or to the western Qinling Shan in the whole Cenozoic. The formation and deformation of the Xining Basin are the direct responses of the India-Eurasia Collision and the growth of the Qinghai-Tibetan Plateau.