Geochronology Geochemistry and Petrogenesis of the Granite and Diorite in Wusun Mountain Western Tianshan

The study object is located in the Chabuchaer Forest Farm on the northern margin of Wushun Mountain in Yili Basin, the studying of geochemistry, geochronology and petrogenesis have an important indicative significance for discussing crust-mantle magmatism in the southern margin of the West Tianshan. The geochemical characteristics show that the monzogranites is a high-potassium-calcium-alkaline and quasi-aluminous-weak peraluminous rocks, the monzogranites is enriched with LREE、weak negative Eu anomaly (δEu=0.74～0.84)、rich in LILEs and deficient in HFSEs(Nb、Ta、Ti、P), its Zr/Hf radios are 42～44, some samples contain a small amount of corundum mineral, and it show the characteristics of crust-derived granite. The Al₂O₃, FeO^T and CaO of the diorite is obviously higher than that in granite, but the Na₂O and K₂O is lower than the granite, it belongs to high-potassium-calcium-alkaline quasi-aluminous rock; the diorite is enriched with LREE、weak positive anomaly of Eu（δEu=0.90～1.24）、rich in LILEs and deficient in HFSEs(Nb、Ta), in addition, the diorite has high Sr (Sr>400×10⁻⁶), low Y (12.83×10⁻⁶) and Yb (1.34×10⁻⁶) and high Mg^#, therefore, the source rock is the partial melting product of the mantle overlying the subduction slab, which enrichment hornblende. The monzogranite and diorite show the characteristics of island arc magma. The zircon U-Pb dating results show that the age of monzogranite is 361.7±1.8 Ma, and belong to the late Devonian. Combined with previous research data, we believed that in ～360 Ma, due to the rolling-back or subduction of the southern Tianshan ocean plate, the overlying mantle partially melted and produced the basic magma. During the uppouring process of the magma, a large amount of heat were provided, which led to partial melting of the crust and the formation of acidic magma, and the two kinds of magma had uneven mixing. At the same time, mantle convection caused by upwelling magma leads to a certain extension (back-arc extension) in the Yili block.