Jurassic sedimentation in the south-central Qiangtang terrane reveals successive terrane collisions in central Tibet

Abstract

Our limited knowledge of Mesozoic tectonism in the Tibetan Plateau has hindered understanding of its geologic evolution. This study uses zircon U-Pb geochronology to refine regional chronostratigraphy and infer the Jurassic sedimentary-tectonic evolution of the Bangong suture and the south-central Qiangtang terrane in the central plateau. During the late Early–early Middle Jurassic, fan delta and alluvial fan deposits sourced from the Amdo basement to the south occurred within the Amdo suture zone, as a result of collision between the Amdo basement and Qiangtang terrane. Since the Bajocian of the Middle Jurassic, continued sea-level rise transformed the Qiangtang terrane into a south-facing shallow continental shelf, and sedimentary detritus was predominantly sourced from the Hoh Xil and Kunlun terranes to the north. The contemporaneous magmatic arc in southern Qiangtang terrane was most likely submerged in a marine setting and did not contribute much detritus to the Middle Jurassic strata. Starting from the early Late Jurassic, a depositional hiatus occurred in the southern Qiangtang terrane, whereas the shallow marine to deltaic deposition in the central Qiangtang terrane received detritus not only from the Hoh Xil and Kunlun terranes to the north, but also from the magmatic arc in southern Qiangtang terrane to the south. The arrival of abundant Jurassic arc-derived detritus in central Qiangtang terrane since ca. 163 Ma was most likely caused by the early Late Jurassic initial collision between the Lhasa and Qiangtang terranes, which raised the southern Qiangtang magmatic arc to be a source region.