Geochronological and Geochemical Study on Liujiaping Granite in the Border Area between Sichuan and Shaanxi Province and Its Tectonic Significance

The Liujiaping granite intrusion is located in Sichuan-Shaanxi border area. The study of the zircon U-Pb geochronology and the geochemistry of the granite aim at discussing its formation and tectonic significance. The results show that the crystallization age of the granite is 825.9±7.8 Ma, which belongs to the mid-Neoproterozoic. The geochemistry analysis shows that the intrusion is low in potassium and rich in sodium and silica (with the average SiO₂ being 75.32%), with peraluminous characteristics. The abundance of the ∑REE varies in the range of (182.13-243.76)×10^-6, with 197.29×10^-6 on average, which shows an enrichment of the LREE and a depletion of the HREE. Chondrite-normalized REE patterns are of the right sea-gull oblique type with the δEu being 0.57, showing a significant negative Eu anomaly. The results of the Nb/Ta, Rb/Sr and Mg^# show that the magmatic rocks of this region originated from the partial melting of the lower crust. With the characteristics of A type granites, the rock formed in the post-collision extensional tectonic setting, which indicates a collision had occurred between the Eastern Bikou terrane and the Yangtze block before 825Ma. The jointing mode of the two blocks is scissors joint from northeast to southwest.