Permian mountain building in the bogda mountains of NW China

The West Bogda Mountains separate the two largest petroliferous sedimentary basins in Northwest (NW) China and may record the evolution history of the Central Asian Orogenic Belt (CAOB). The timing of the initial uplift of the West Bogda Mountains is debated, which may provide the robust constraint on the CAOB evolution. Here we present an integrated study of sedimentology, geochemistry, and detrital zircon geochronology to constrain the timing of the initial uplift of the West Bogda Mountains. The late Lower Permian Lucaogou Formation in the West Bogda Mountains is dominated by organic-rich laminated shale, gravity flow deposits and dolomite without shallow-water sedimentary structures, suggesting a deep-water lacustrine depositional environment. The Middle Permian Quanzijie Formation is mainly composed of poorly sorted and sub-rounded conglomerate, which indicates that the depositional environment changed to an alluvial fan. The depositional environment changed to a meandering river system in the early Upper Permian Wutonggou Formation, with evidence from the widely developed cross-bedding in its sandstone and the typical ‘dual structure’. The compositions of immobile elements and detrital zircon U-Pb geochronology reveal changes in sediment sources from the early to late Permian. The sediments of the late Lower Permian Lucaogou Formation were mainly sourced from the North Tianshan, while the sediments in the Middle Permian were mostly locally derived. Combining these evidences, we infer that the initial uplift of the West Bogda Mountains likely occurred in the period from the late Lower to Middle Permian (~289.8 Ma to ~265.7 Ma), and was probably caused by the intracontinental collision between Junggar Block in the north and the Tarim Block in the south.