Geochemistry,Geochronology Characteristics and Tectonic Significance of Yitiaoshan Diorite in the Southern Margin of Beishan Orogenic Belt

The Yitiaoshanbei diorites are located between the Beishan orogenic belt and Dunhuang terrane. The study of these diorites has important geological implications for the Paleozoic tectonic evolution and geodynamic processes of the Beishan orogenic belt. In this study, we present zircon U-Pb ages, and whole-rock major and trace element compositions for diorites from the Yitiaoshanbei area. LA-ICP-MS zircon U-Pb dating suggests that Yitiaoshanbei diorites were emplaced at the Early Permian(ca. 274.6 Ma). Geochemical characteristics imply that these diorites belong to the metaluminous and calc-alkaline series rocks. These diorites are enriched in large ion lithophile elements(LILEs; e.g., Rb, Th, K, U and Pb), and depleted high field strength elements(HFSEs; e.g., Ba，Nb, Ta, Ti, P, Zr and Hf). The Early Permian Yitiaoshanbei diorites were derived by partial melting of lower crustal materials, induced by lithospheric mantle magmatism and mixed with a small amount of mantle derived basaltic magma.Along with related discriminant diagrams and regional geological data, we suggest that the Yitiaoshanbei diorites were generated in a post-collisional extensional setting. These results also indicate that the southern belt of the Beishan has been underwent post-collisional stage or partially entered the post collisional evolution stage during the Early Permian.