LA-ICP-MS zircon U-Pb dating and tectonic setting of Zhongchuan intrusion, Lixian area, western Qinling orogen

Located in the middle of western Qinling orogen, the Zhongchuan intrusion is closely related to mineralization. The main intrusive body consists of biotite adamellite, which is generally considered to have been formed in Indo-Chinese epoch. LA-ICP-MS zircon U-Pb ages and major and trace elements of whole-rock were determined for Zhongchuan intrusion. The results show that the intrusion belongs to high-K calc-alkaline series with high content of Na2O, K2O and low content of MgO. Chondrite-normalized REE patterns are characterized by strong LREE enrichment and variable degrees of negative Eu anomalies (δEu=0.60～0.67) ; The ORG normalized trace element patterns show that the intrusion is enriched in LILE (K, Th, Rb) and depleted in HFSE (Ta, Nb, Y and Yb) . The Zhongchuan intrusion basically shows the characteristics of low content of Sr and Yb and was formed in the syn-collision circumstances. U-Pb age determination of zircon indicates that the earliest biotite adamellite intruded at 264.4±1.3Ma in the Late Permian, earlier than 219-232Ma. Taking into account the tectonic environment, the authors hold that the continent-continent collision of western Qinling area began at the end of Permian and lasted to Triassic.