Late Triassic basin inversion of the Qiangtang Basin in northern Tibet: Implications for the closure of the Paleo-Tethys and expansion of the Neo-Tethys

Abstract

Sedimentologic and tectonic records in the Qiangtang Basin, northern Tibet, indicate a negative basin inversion during the Late Triassic, which reveals Paleo-Tethys closure and Neo-Tethys expansion. In the Triassic sedimentary succession, there is a clear sedimentary facies shift. The Middle Triassic to Carnian (Late Triassic) sequence displays typically shallowing-upward changes related to regional uplift and terrestrial erosion. On the other hand, the Norian (Late Triassic) to Middle Jurassic sequence has typically deepening-upward changes due to the tectonic subsidence and transgression. The negative basin inversion underwent a transition from previous marine environment to terrestrial erosion in the North Qiangtang depression but a terrestrial erosion to marine environment transition in the South Qiangtang depression during the Late Triassic. Elemental data show bimodal volcanic rocks for the Nadi Kangri Formation with intracontinental rift setting. The initial negative inversion started with the Nadi Kangri bimodal volcanic eruption and alluvial/fluvial basal conglomerate that overlapped angular unconformably, disconformably, or conformably on the underlying formations. The U-Pb ages of volcanic samples from the Nadi Kangri Formation range from ∼220 to 201 Ma, and its initial eruption age (∼220 Ma) represents the onset time of negative basin inversion. Our data reveal that the exhumation of northern Qiangtang foreland basin during the early Late Triassic recorded the closure of the Paleo-Tethys Ocean and its branches along the Hoh Xil–Jinshajiang and the Longmu Co–Shuanghu, respectively. The initiation of Qiangtang rifting during the late Late Triassic could be related with the rapid expansion of the Neo-Tethys Ocean along the Bangong–Nujiang.