Zircon SHRIMP U-Pb dating of gneissic granite bodies in the Lubai Mountain of Hami, Xinjiang, and its geological significance

Abstract：Some gneissic granite bodies are exposed in the Lubai Mountain of Hami area, Xinjiang. Zircons from these rocks were dated at （1453±15） Ma by SHRIMP, suggesting that their intrusion occurred in middle Proterozoic. Data of major elements and trace elements show that the gneissic granite bodies are enriched in MgO, FeOt, CaO, depleted in alkaline-earth metals and have low K2O/Na2O ratios. REE partition patterns are inclined to the right. The lithophile elements are obviously concentrated whereas Nb and Ta are depleted relative to MOR granite, suggesting characteristics of I type granite. These data provide important information for the possible geological event of the closure of South Tianshan Ocean in Proterozoic.