Geochronology, geochemistry and tectonic significance of Guniujiang A-type granite in Anhui Province
安徽牯牛降A型花岗岩的年代学、地球化学和构造意义

The Guniujiang intrusion in southern Anhui Province is located at the southeastern boundary of Yangtze plate, and situated in Jiangnan uplift. Here we report new zircon U-Pb age and geochemical data, and discuss the petrogenesis and tectonic significance of the Guniujiang granite. Laser ablation ICP-MS zircon U-Pb dating suggests that the age of the Guniujiang granite is 130.1±1.3Ma (95% confidence, MSWD=0.55). Combined with other available high-precision zircon U-Pb data, the ages of these granites from southern Anhui are mainly concentrated in 125~130Ma. The Guniujiang granite is a high calc-alkaline and metaluminous granite with SiO2 contents of 72.21%~74.85%, and high K2O (>5.11%), Fe values (FeOT/(FeOT+MgO)>0.91), and K2O/Na2O ratios (>1.61). The rock also shows relatively high Zr, Nb, Y and Ga concentrations, enriched in REE (>419×10-6) and strong incompatible elements such as Rb, Th and U, low CaO and MgO, extremely depleted in Ba, Sr, and Eu (Eu*/Eu=0.29~0.30). The geochemical characteristics indicate that this granite belongs to A-type. The very low Mg# values (0.14~0.16) and relatively low Cr concentration (Cr=10×10-6), high Yb (7.08×10-6~9.02×10-6), Y (78.7×10-6~90.8×10-6) concentrations and Th/U ratios (5.17~7.79) show that the partial melting of old continental crust materials might have been the main mechanism for petrogenesis of the Guniujiang granite. The Guniujiang granite can be classified into A2 subtype, which is usually believe to be formed under a post-collision extensional tectonic setting.