Petrogenesis of granitoids in the southern Anhui Province, China: Implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogenic belt

Abstract

The Jiangnan orogenic belt is a key component of the South China Block, yet the tectonic-magmatic evolution of the orogenic belt remains widely debated. The eastern segment of the Jiangnan orogenic belt experienced Neoproterozoic magmatism evidenced by widespread granitoids, which is key to understanding the tectonic evolution of the orogenic belt. In this study, we conducted detailed field, petrographic, geochemical, and geochronological studies of the Neoproterozoic Xucun pluton and adjacent magmatic rocks in the southern Anhui province of the eastern Jiangnan orogenic belt. Zircon LA-ICP-MS U-Pb dating of two samples yields interpreted crystallization ages of 830.3 ± 2.9 Ma and 831.2 ± 3.3 Ma. The Xuun pluton is an S-type, peraluminous biotite granodiorite that belongs to the calc-alkaline to high-K calc-alkaline series. εNd(t) values for the pluton range from −2.53 to −0.49, and the TDM2 model ages range from 1.66 to 1.83 Ga. The whole-rock, major and trace element and Sm-Nd isotopic compositions of the Xucun pluton suggest petrogenesis in a magmatic arc-related tectonic setting. These new constraints, combined with previous results, indicate that the Xucun pluton formed in a post-collisional tectonic setting. The source for the Xucun pluton was mainly juvenile crust mixed with some Mesoproterozoic continental crust. The juvenile crustal rocks were generated during arc magmatism before ca. 860 Ma. We interpret that the the eastern Jiangnan orogenic belt was generated during the ca. 860–830 Ma collision of the Shuangxiwu arc and a continental terrane. Subsequent collapse of the Jiangnan orogenic belt resulted in erosion and partial melting of juvenile crustal rocks to form S-type granitoids, including the Xucun pluton.