西藏东巧—北拉地区班公湖—怒江洋俯冲闭合及对南羌塘盆地演化的制约OA北大核心CSTPCD

The Bangong Lake-Nujiang suture zone is an extreme important tectonic boundary in the Tibetan Plateau which is not only closely related to evolution of the Tethyan tectonic domain,but also directly controls the formation and inversion of the Mesozoic southern Qiangtang oil and gas-bearing basin.Based on stratigraphic correlation,sandstone petrography analysis and detrital zircon U-Pb dating,this paper reconstructs provenance changes in the Dongqiao-Beila area and reveals multi-stage subduction processes and microblock amalgamations in the central Bangong Lake-Nujiang Ocean(BNO).The BNO branch(Amdo Ocean)at Dongqiao-Beila area began to subduct in the Early Jurassic,resulting in amalgamation of the Amdo block to the southern Qiangtang terrane and rifting the Dongkaco microblock away from the northern Lhasa terrane and formed two new BNO branches of the Dongqiao Ocean to the north and Beila Ocean to the south.The lower Xihu Group close to the Beila suture in the south of the Dongkaco micoblock shows recycle deposits from the underlying Upper Triassic Quehala Group,while the upper Xihu Group close to the Dongqiao suture in the north of the Dongkaco microblock began to receive detritus from the southern Qiangtang terrane,indicating the Dongqiao Ocean demised and the Dongkaco microblock has amalgamated on the southern margin of the Qiangtang terrane with a peripheral foreland basin developed during the Middle Jurassic.Subsequent subduction of the Beila Ocean droved the Dongkaco microblock continuing to converge with south Qiangtang terrane in the Middle Jurassic and promote abundant materials from the south Qiangtang terrane transporting into the Middle-Upper Jurassic Jienu Group in the foreland basin on the Dongkacuo microblock.Wide collision between the Qiangtang and Lhasa terrane occurred during the latest Jurassic and Early Cretaceous(147-141 Ma)and continued during Aptian(ca.120 Ma)until the Beila Ocean finally dimed at Dongqiao-Beila Area. In response to multi-stage northward subductions of the BNO,the south Qiangtang Basin changed from passive continental margin to active continental margin during earliest Jurassic and developed arc-related basin system of east-west extending back-arc basin,volcanic arc and fore arc basin from north to south.The Lower Jurassic Quse black shale and overlying Buqu bioclastic limestone deposited in the back-arc basin.Continuous convergence and microblock collision contributed to rapid regression and uplift of the south Qiangtang basin,resulting in the deposition of tidal Xiali Formation with gypsum and mudstone during the Middle Jurassic.As the result of collision between the Lhasa and Qiangtang terrane in the Early Cretaceous,the south Qiangtang Basin evolved in fold thrust belt of the peripheral foreland basin and resulted in differential burial and denudation of the Jurassic successions.During the Late Jurassic-Early Cretaceous,the Quse black shale and Buqu bioclastic limestone were correspondingly buried rapidly due to the tectonic compression and entered the stage of oil generation and dolomitization,making it become the most important accumulation period in the south Qiangtang Basin.