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.

西博格达山分隔了中国西北（NW）境内两个最大的含油气沉积盆地，其演化历史或可记录中亚造山带（Central Asian Orogenic Belt, CAOB）的演化历程。西博格达山的初始隆升时间尚存争议，而该时间可为中亚造山带的演化提供可靠约束。本文整合沉积学、地球化学与碎屑锆石年代学研究方法，对西博格达山的初始隆升时间进行限定。
西博格达山内下二叠统晚期芦草沟组以富有机质纹层页岩、重力流沉积与白云岩为主，未见浅水沉积构造，指示深水湖相沉积环境。中二叠统泉子街组主要由分选差、次圆状砾岩组成，表明沉积环境转变为冲积扇体系。上二叠统早期梧桐沟组的沉积环境演变为曲流河体系，其砂岩中广泛发育的交错层理与典型的“二元结构”可为该结论提供佐证。
惰性元素组成与碎屑锆石U-Pb年代学结果揭示了二叠纪早晚期沉积物源的变化。下二叠统晚期芦草沟组的沉积物主要来自北天山，而中二叠统沉积物则多为局地物源。
综合上述证据，我们推断西博格达山的初始隆升大致发生于下二叠统晚期至中二叠世（约289.8 Ma至约265.7 Ma），其成因可能与北部准噶尔地块与南部塔里木地块的陆内碰撞有关。