800~780Ma continental rift magmatism in the eastern part of the Jiangnan Orogen: Implications from~790Ma aluminous A-type granites in Zhejiang-Anhui-Jiangxi border area

In this paper, the authors report geochronological and geochemical data obtained for Lingshan granite porphyries of the eastern Jiangnan Orogen in the Zhejiang-Anhui-Jiangxi border area. Zircon LA-ICP-MS U-Pb dating of Lingshan granite porphyries shows that these rocks were crystallized at 791.8±2.6Ma. Lingshan granite porphyries are characterized by high Si, high TFeO/ (TFeO+MgO) ratio, low Mg, Ca, Mn, and P, and peraluminous nature (A/CNK=1.04~1.18); REE data show that the granite porphyries have high concentrations of Rb, Ga, Th, Zr, Y, but are depleted in Sr, P, Ti, Ba; additionally, the granite porphyries have high total REE concentrations and high LREE/HREE ratio, exhibiting strong negative Eu anomalies; these characteristics are consistent with features of the typical aluminous A-type granite. Geochemical analysis and results of previous researches show that the Lingshan granite porphyries were formed in a continental rift environment, and most likely derived from partial melting of juvenile crust. In combination with the previous study, the authors hold that the magmatic activities that occurred between 800 and 780 Ma not only played an important role in the formation of South China Neoproterozoic basin but also has important geological significance for the study of the tectonic environment during this period and calibration of sedimentary cycle during Banxi period.