U-Pb Chronology of Detrital Zircons from the Carboniferous Sequences and its Geological Implications in West Junggar

The exposed strata in Karamay district, West Junggar in Xinjiang, are comprised mainly of the Lower Carboniferous Xibeikulasi, Baogutu and Tailegula Formations, a series of thick bathyal continental slope facies clastic sedimentation. The stratigraphy and ages of the sedimentary rocks are still a matter of debate. This paper focuses on the U-Pb chronology of detrital zircons from the Xibeikulasi and Tailegula Formations in this area, in purpose of constraining the age of the formations, reconstructing the geological sequences, determining the source material and further discussing the tectonic evolutionary history of West Junggar. Detrital zircon dating of the Xibeikulasi Formation gives two young age peaks of 309.3 Ma and 331 Ma, respectively. The same dating method on the Tailegula Formation gives two young age peaks of 304 Ma and 318 Ma, respectively. The youngest age peaks in those two formations match with the peak period of post-collisional magmatism in West Junggar. The maturity of the sandstones in this region is low, which may relate to the undivided volcanogenic arc, suggest almost the same time between the secondary peak age of detrital zircons and volcanic activities. Hence, the second young age peak could roughly indicate the strata sedimentary period. No Precambrian zircon has been founded among those detrital zircons, which suggests that the crystallized Precambrian basement may not exist, or the basement is small and scattered distribution, cannot be the source of carboniferous strata in West Junggar.