Triassic closure of South Tianshan Ocean: Evidence from provenance analysis of High-Pressure relics-bearing fore-arc sediments and multi-disciplinary data

Abstract A major debate concerning the final welding time of southern Altaids has led to considerable uncertainty regarding the configuration of northeast Pangea and the reconstruction of proto-Asia. Here we report Triassic provenance deposited in a fore-arc accretionary basin closely located with the Akeyazi LT-UHP metamorphic complex in the South Tianshan Orogenic Belt (STOB). Field-based detrital zircon U-Pb analysis of sandstones yield a maximum depositional age of the early Triassic (~ 231.7 ± 1.1 Ma) with a major early Permian peak and few Precambrian records. Hf isotopic analysis, accompanying with multi-disciplinary data compilation, indicate the early Triassic sediment received additional detritus from distal juvenile East Tianshan Arc region, rather than from any proximate tectonic units or a missed intra-oceanic arc. A hypothesis is proposed for STOB geodynamic model with introducing temporary flat subduction beneath the Central Tianshan Arc region. Available data advocates the STO, which serves as an accessory ocean basin paleo-geographically belonging to the Paleo-Asian Ocean, may have been closed in the early Triassic.