Late Cenozoic geological evolution of the foreland basin bordering the West Kunlun range in Pulu area: Constraints on timing of uplift of northern margin of the Tibetan Plateau

With an average elevation of 5000 m the West Kunlun range marks northwestern margin of the Tibetan Plateau and formed as an orogen in response to the collision of India and Asia 50 Ma ago. Its history of uplift and erosion in the late Cenozoic is recorded in a unique sedimentary sequence exposed through the highest terrace along the southern margin of the Tarim basin in Pulu area. The terrace is composed of coarse-grain conglomerate at the bottom, alkaline-enriched volcanic rocks in the middle and eolian sediments on the top. The underlying basement rocks are formed by Neogene rocks and Paleozoic granite. Named the Xiyu conglomerate, the coarse-grained conglomerate is assigned a depositional age in the late Pliocene and the early Pleistocene (3.4-1.6 ma) and generally considered to be the products of rapid uplift of the Tibetan Plateau. To reveal the relations between uplift, erosion, and sedimentation, we have collected samples of granite overlain by the Xiyu conglomerate for dating the fission track age of apatite. The fission track ages date the absolute time of cooling through the track retention temperature of the granite within the West Kunlun range to be Miocene to early Pliocene (20-4.8 Ma). The cooling event was coeval with the north-verging thrusting along the northern boundary fault and the associated foreland basin deposition, suggesting that the West Kunlun range once underwent significant tectonic uplift in the Neogene. In contrast to the underlying Tertiary foreland basin strata, the Xiyu conglomerate thins toward the West Kunlun range and contains granite pebbles of cooling ages of 93, 18, and 12 Ma. Our study suggests that the primary cause for accumulation of the Xiyu conglomerate and the correspondent sediments is the increase of erosion and sedimentation rates after the main pulse of tectonic uplift due to Quaternary climate change.