Jurassic evolution of the Qaidam Basin in western China: Constrained by stratigraphic succession, detrital zircon U-Pb geochronology and Hf isotope analysis

The formation and evolution of an intrac-ontinental basin triggered via the subduction or collision of plates at continental margins can record intracontinental tectonic pro-cesses. As a typical intracontinental basin during the Jurassic, the Qaidam Basin in western China records how this extensional basin formed and evolved in response to dis -tant subduction or collisional processes and tectonism caused by stresses transmitted from distant convergent plate margins. The Jurassic evolution of the Qaidam Basin, in terms of basin-filling architecture, sediment dispersal pattern and basin properties, re-mains speculative; hence, these uncertainties need to be revisited. An integrated study of the stratigraphic succession, conglomerates, U-Pb geochronology, and Hf isotopes of de-trital zircons was adopted to elucidate the Jurassic evolutionary process of the Qaidam Basin. The results show that a discrete Juras-sic terrestrial succession characterized by alluvial fan, braided stream, braided river delta, and lacustrine deposits developed on the western and northern margins of the Qaidam Basin. The stratigraphic succession, U-Pb age dating, and Hf isotope analysis, along with the reconstructed provenance results, suggest small-scale distribution of Lower Jurassic sediments deposited via au-tochthonous sedimentation on the western margin of the basin, with material mainly originating from the Altyn Tagh Range. Lower Jurassic sediments in the western seg-ment of the northern basin were shed from the Qilian Range (especially the South Qilian) and Eastern Kunlun Range. And coeval sedi-ments in the eastern segment of the northern basin were originated from the Quanji mas-sif. During the Middle-Late Jurassic, the pri-mary source areas were the Qilian Range and Eastern Kunlun Range, which fed material to the whole basin. The Jurassic sedimentary environment in the Qaidam Basin evolved from a series of small-scale, scattered, and rift-related depressions distributed on the western and northern margins during the Early Jurassic to a larger, extensive, and uni-fied depression occupying the whole basin in the Middle Jurassic. The Altyn Tagh Range rose to a certain extent during the Early Ju-rassic but lacked large-scale strike-slip tecto-nism throughout the Jurassic. At that time, the North Qaidam tectonic belt had not yet been uplifted and did not shed material into the basin during the Jurassic. The Qaidam Basin experienced intracontinental exten-sional tectonism with a northeast-southwest trend throughout the Jurassic in response to far-field effects driven by the sequential northward or northeastward amalgamation of blocks to the southern margin of the Qa-idam Block and successive accretion of the Qiangtang Block and Lhasa Block onto the southern Eurasian margin during the Late Triassic-Early Jurassic and Late Jurassic- Early Cretaceous, respectively.