Zircon U-Pb age and tectonic genesis of the granite in the Beizhan iron ore deposit of western Tianshan, Xinjiang

The Awulale Mineralization Belt in the Western Tianshan Mountains is one of the important iron mineralization belts in China, but there is still controversy over the genetic types and tectonic environment of iron deposits in this mineralization belt.The main reason for the inconsistency in understanding is the lack of in-depth research on the iron-bearing volcanic rocks and granites intruded into them, especially on the granites that may be related to mineralization.By studying the zircon U-Pb age and rock geochemical data of the granites in the Beizhan iron mining area of the Awulale Metallogenic Belt, this paper aims to explore their genesis and tectonic environment and provide new information on the genesis of iron deposits in the Western Tianshan.LA-MC-ICP-MS zircon U-Pb dating of the granites in the Beizhan iron mining area represent that the age of the K-feldspar granite is 321.5±3.6 Ma, and the age of the granite porphyry is 308±1.2 Ma, which was formed in Late Carboniferous.The geochemical characteristics of the rock samples show that they have high K₂O+CaO contents and are characterized by quasi-aluminous features; the chondrite normalized distribution pattern of rare earth elements shows steep left and gentle right, and δEu value is strongly negative; trace elements analysis show enrichment in Rb, K, Th, Sr, U, etc., and depletion in Ba, Nb, Ta, Ti, P and other elements.Combined with the tectonic environment discrimination diagrams, it is believed that they were formed in a post-collisional environment.The ε_Hf(t)values range between 5.7~13.3 and 7.5~12.5, with average values of 10.91 and 10.06 respectively, which are higher positive values.The Hf two-stage mode ages t_MD2 are between 479~947 Ma and 526~843 Ma, with average ages of 700 Ma and 679 Ma, respeetively.Based on comprehensive regional research results, it is believed that the Late Carboniferous Awulale Iron Metallogenic Belt of Western Tianshan was formed in a period of tectonic transition, and may be post-collision stage from convergence to extension evolution.During this period, granite in Beizhan region was formed.