Sm-Nd isochron age evidence for Precambrian metamorphic rocks from the eastern Junggar in northern Xinjiang, China

The characterstic of the basement of Junggar block has been a topic of long-standingdebate.Based on the data of gravity and magnetic anomaly,some researchers deduced thatthere were Precambrian basic-ultrabasic complex on the basement of Junggar block.However,others maintained that the basement of Junggar block was probably the Paleozoicoceanic crust because of the lack of isotopic evidence and older outcrops aroundthe Junggar Basin. In recent years,molecules of fossil community were discovered from Aleandao Groupat the Qingshuiquan and Kamuster of eastern Junggar.Most of the fossils,such asPylocorpus,Retincnlafopora,Asteropyla,were found at the boundary between Cambrianand Sinian in Qinling and South China.An isotopic age of 1908 Ma for leuco-pink graniticgneiss from the lower Huangcaopo Group was gained by evaporated Pb-isotope method forsingle zircon in Xiaoluigou of eastern Junggar by Zhang et al.But all of these results onlyindicate a possibility that the basement of Junggar block consists of Precam