Confirmation of gneissic granite of Qingbaikou period and its constraint on the timing of the Rodinia supercontinent on the Altun orogenic belt

The study of the Neoproterozoic granites in the Altun orogenic belt is significant for revealing the area of the Rodinia supercontinent convergent stage tectonic evolution. In this paper, a detailed study of petrology, chronology and geochemistry was carried out for a new division of Qingbaikou gneissic granite in Yaganbuyang area. The U-Pb dating of zircons from the gneissic granite using LA-ICP-MS yielded (883.0±3.3)Ma and (883.1±3.3)Ma, indicating that the gneissic granite was generated in Qingbaikou period. The geochemical analysis shows that major elements are characterized by high SiO₂, Al₂O₃ and K₂O values and low Na₂O, MgO, CaO and TiO₂ values, thus belonging to the calc-alkaline-high-K calc-alkaline series, and peraluminous.REE distribution patterns show negative anomaly of Eu, obvious fractionation of LREE and weak fractionation of HREE, with a clear V trough, which shows the features of crustal derived granite. The gneissic granite is rich in large ion lithophile elements of Rb, Th, LREE, slightly depleted in Ba and mightily depleted in high field strength elements of Nb, Sr, P, Hf, Ti. These characteristics are similar to features of the continental collision type granite. The source rock of the gneissic granite was formed by the partial melting metasandstone from the crust in the subduction-collisional environment about Rodinia supercontinent. Comprehensive study shows that these syn-collisional granites were generated between 871 Ma and 940 Ma, which constrained the timing of the Rodinia supercontinent in Early Neoproterozoic along the Altun orogenic belt. These rock bodies have the characteristics of zonal distribution in space and confirm the existence of syn-collisional granites belt about Rodinia supercontinent on the Altun orogenic belt.