Final closure of the Paleo Asian Ocean basin in the early Triassic

The timing of the final welding of the southern Altaids to construct Pangea is a matter of debate which has led to considerable uncertainty regarding the configuration of northeast Pangea and the reconstruction of proto-Asia. Here we investigate the provenance of sediments deposited within a fore-arc accretionary basin located close to the Akeyazi low temperature ultra-high pressure metamorphic complex in the South Tianshan Orogenic Belt. Detrital zircon U-Pb analysis of sandstones yields a maximum depositional age in the early Triassic (around 231.7 million years ago) with a major early Permian peak and few Precambrian records. Bulk-rock composition and zircon Hf isotopic analysis, combined with a compilation of existing data, indicate the early Triassic sediment received additional detritus from the distal juvenile East Tianshan Arc region, rather than from any proximate tectonic units or an intra-oceanic arc. Available data suggests that the South Tianshan Ocean, an accessory ocean basin to the Paleo-Asian Ocean, could close in the early Triassic.