Geochemistry and detrital zircon geochronology of the Bagong Formation clastic rocks in the Queerchaka area, central part of the Qiangtang Basin: evidence for the Late Triassic chemical weathering and tectonic evolution

Abstract

Late Triassic was not only a key episode for the evolution of the Qiangtang Basin but also a critical interval marking the final closure of the Paleo-Tethys Ocean on the Qinghai–Tibet Plateau. However, the nature of the Late Triassic Qiangtang Basin and its response to the evolution of the Paleo-Tethys Ocean remain unclear. Here, elemental geochemistry and detrital zircon U–Pb dating data of clastic rocks from the Upper Triassic Bagong Formation in the Queerchaka area (central part of the Qiangtang Basin) were integrated to infer the chemical weathering history, provenance, and tectonic evolution during the Late Triassic. The Bagong Formation may be assigned to the Carnian–Norian of the Late Triassic. Chemical Index of Alteration (CIA) values of the studied samples, which were unaffected by sedimentary recycling and K-metasomatism, reveal a moderate chemical weathering (CIA = 68.3–75.8). Multiple geochemical proxies and zircon U–Pb age distributions suggest a felsic provenance for the Bagong Formation in the Queerchaka area. This provenance was primarily derived from the complex rocks of the Central Uplift Belt, with a minor contribution from the Hoh Xil–Jinshajiang complex rocks. The Late Triassic Northern Qiangtang sub-basin may be a back-arc compound foreland basin that linked to a double subduction and collisional orogenic process involving the northward subduction of the Longmuco–Shuanghu Paleo-Tethys branch Ocean and the southward subduction of the Hoh Xil–Jinshajiang Paleo-Tethys Ocean. These findings provide a foundation for deciphering the nature and dynamic processes of the Late Triassic Qiangtang Basin.