Depositional and detrital zircon geochronological records of Carboniferous system in Wushi, Northwest Tarim Basin: Implications for tectonic evolution

The Visean to Bashkirian profile is well exposed in the Wushi area, the northwestern margin of the Tarim Basin, Northwest China. Numerous sandstone samples were chosen to carry out U-Pb and Lu-Hf isotope test by LA-ICP-MS method. Based on detailed analysis of geochronology, heavy minerals, sandstone skeleton component, this research further explores sedimentary evolution and its geodynamic mechanism about the Tarim Basin and the periphery orogen in Carboniferous. Sandstone skeleton component analysis shows that sandstone grains are dominated by quartz, and volcanic-metavolcanic is lithic fragments. Its main provenance is the recycled orogen, and has the trend to migrate to the inner craton from the bottom to top. The main proportions of heavy mineral assemblages are stable heavy minerals, such as zircon, tourmaline, TiO2 minerals. Heavy mineral analysis reflects the distant source and relatively stable tectonic setting are possible. The geochronological results show that the four samples have approximately similar U-Pb age patterns and Hf isotopic compositions, mainly reflecting multiphase tectono-thermal events with age groups of 392 similar to 496Ma, 708 similar to 868Ma, 893 similar to 1044, with epsilon(Hf)(t) ranged from -15 to 13. In addition, there are also a small amount of 1713 similar to 1917Ma, 2376 similar to 2606Ma age. The geochronological information and provenance system are very similar to Silurian to Devonian strata underlying the unconformity. Comparing with the main potential source areas, the main provenance is the northern Tarim palaeohigh. The redeposition of pre-Carboniferous strata in Tarim Basin, associated with the erosion source in the Kunlun-Altun orogen, may also have some contribution, and became the mainly provenance of detrital zircon of 893 similar to 1044Ma before Early Visean; while the two facts, detrital composition maturity increased and the abundance of 893 similar to 1044Ma decreased rapidly, suggested that the material from the latter source diminished, and the mature material from the palaeohigh raised after Late Visean. In other words, although the radiolarian information shows that the South Tianshan Ocean had closed after Early Visean, the provenance system didn't change greatly until Bashkirian, and the information about collision, orogenic events and their effects of the South Tianshan and the Tarim hadn' t been recorded.