Zircon U-Pb ages, geochemical characteristics and geo-logical significance of Yaganbuyang gneiss in Qingbaikou period along the Altun orogenic belt

The Yaganbuyan gneiss is outcropped in the Kumutashisayi area of the Azhong Block. The gneiss rocks are composed mainly of biotite plagioclase gneiss and biotite monzonitic gneiss. The U-Pb dating of zircons from the gneiss using LA-ICP-MS yielded an age of 900.2 ±2.9Ma, which indicates that Yaganbuyan gneiss was generated in Early Neoproterozoic. Geochemical analy-sis shows that major elements are characterized by high SiO₂, Al₂O₃ and K₂O+Na₂O content, and low Na₂O, MgO, CaO and TiO₂ content, with A/CNK being 0.95~1.22, suggesting that the granite belongs to the typical high-K calc-alkaline series with peralumi-nous nature. The gneisses are enriched in large ion lithophile elements of Rb, Th, K and depleted in high field strength elements of Nb, Sr, P, Hf, Ti. These characteristics are similar to features of the continental collision type granite. REE distribution patterns show negative anomaly of Eu and distinct enrichment of LREE relative to HREE. The chondrite-normalized REE patterns are right-in-clined, with a clear Ⅴ trough. The source rock of the gneiss was mainly from the partial melting of sedimentary rocks in the crust and generated in a subduction-collisional environment. These features indicate that the Yaganbuyan gneiss was formed in the Neopro-terozoic, and that a subductional collision event took place in the Qaidam microplate and the Azhong plate, which coincides with the assembly event of the supercontinent Rodinia.