Zircon U-Pb-Lu-Hf Isotopic Characteristics and Geological Implications of Mesozoic Granites in Western Qinling

LA-ICP-MS zircon U-Pb isotopic analyses reveal that the granitoid intrusions of Zhongchuan, Baijiazhuang and Jiaochangba in Western Qinling orogeny emplaced at ages of 220±1, 216±6 and 222±6 Ma, respectively, showing that all of them belongs to Middle-Late Triassic granitoid magmatism. Whole rock geoche-mistry analyses indicate that the primitive mantle-normalized trace element patterns and Chondrite-normalized REE patterns of the rock samples from the three intrusions show significant similarity, for example, depletion in high field strength elements of Nb, Ti and P, and enrichment in LREE. Analyses for zircon Lu-Hf isotopes indicate that the εHf(t) values range from -3.31 to +1.68 of the three intrusions with the two-stage model ages between 1151 and 1456 Ma. Petrogenetic studies indicate that the granitoid magmas of these Indosinian granitoid intrusions were derived mainly from the partial melting of mesoproterozoic crust material. Combined with the formation age, petrogenesis and tectonic background, these Indosinian intrusions were most likely formed in the collision process between South Qinling orogen and South China Block along Mianlue suture zone, and might be related to the subducted slab break off of South China Block. © 2020 Peking University.