Geochronology and geochemistry of volcanic−sedimentary successions in the Qiangtang terrane: Implications for provenance and the tectonic evolution of late Paleozoic−early Mesozoic central Tibet

The Paleozoic−Mesozoic tectonic evolution of the central Tibetan Qiangtang terrane and the opening and closure of the Paleo-Tethys Ocean remain debated. By integrating lithofacies observations with geochemical data and detrital zircon U-Pb geochronology from key pre-Ordovician to Jurassic volcanic−sedimentary successions of the Qiangtang terrane—particularly those within the Central Uplift Belt—we constrain the lithology and magmatic−tectonic setting of volcanic rocks, reconstruct the chemical weathering history and provenance of sedimentary rocks, and thereby elucidate the Paleozoic−Mesozoic tectonic evolution of the region. In the southern Qiangtang terrane, most Carboniferous−Permian mafic rocks were derived from a depleted mantle source in a continental arc setting and were primarily influenced by melts from subducted sediments, whereas the Triassic granites originated from an enriched mantle source within an alkaline arc setting. In the northern Qiangtang terrane, Permian volcanic rocks formed in an oceanic arc environment. The tectonic settings inferred from sedimentary and volcanic rocks are consistent. Pre-Ordovician and most Carboniferous−Permian samples indicate a passive margin setting, while the Triassic samples reflect an active margin setting. Sedimentary rocks experienced limited sediment recycling and transport, with the chemical weathering index controlled by grain size and hydraulic sorting rather than by recycling. Carboniferous and Triassic samples exhibit weak chemical weathering, whereas most Permian samples display moderate chemical weathering. Combined with the provenance analysis, the results indicate that the Paleo-Tethys Ocean formed prior to the Permian. During the Early Permian, the Qiangtang terrane separated from the Gondwana supercontinent. In the Late Permian, the Paleo-Tethys Ocean continued to subduct northward, and slab rollback induced asthenospheric upwelling into the subduction zone, leading to the development of a proto-uplift in central Qiangtang. During the Early to Middle Triassic, the Shuanghu Paleo-Tethys experienced subduction, and diachronous collisions between the northern and southern Qiangtang terranes from east to west produced subduction-related mélanges and high-pressure rocks, while the Central Uplift continued to rise. In the Late Triassic, the closure of the Paleo-Tethys Ocean resulted in the uplift and erosion of the Central Uplift.