Unraveling the early Paleozoic tectonic history of the South Qinling Belt: Evidence from geochronology, geochemistry, and Sm-Nd isotopes of meta-sedimentary rocks

The determination of the petrogenesis and age of meta-sedimentary rocks plays a crucial role in enhancing our understanding of regional tectonic evolution. In this study, we conducted comprehensive geochemical, zircon UPb, and Sm-Nd isotope dating analyses of the biotite gneiss of the Changjiaoba group to investigate the tectonic evolution of the South Qinling belt. The age range of detrital zircons from the biotite gneiss was estimated to be 446-2798 Ma, with prominent peaks observed at approximately 454, 660, 790, 1998, and 2770 Ma. The earliest data indicate that the final sedimentary age of the Changjiaoba group corresponds to the late Ordovician. The protoliths of the biotite gneiss were argillaceous rocks, classified as parametamorphic rock. The chondritenormalized rare earth element (REE) diagram exhibited right-inclined patterns with negative Eu anomalies. The upper continental crust (UCC)-normalized trace element patterns exhibited insignificant enrichment of Ba, Sr, and K; negative anomalies of Hf, Th, U, and Ti; and depletion of Cr and Ni. Geochemical indicators suggest that the precursor sediments are felsic rocks that have undergone moderate weathering. The epsilon Nd (t) values of the biotite gneiss (-10.2 to -3.4) suggest a mixture of a few juvenile crust components and abundant ancient material, indicating an arc-realted setting. Collectively, our findings suggest that the primary material sources of the Changjiaoba group were predominantly the North Qinling belt during the Paleozoic and the Yangtze block during the Neoproterozoic. The tectonic setting discrimination diagrams imply that the biotite gneiss were formed in an active continental margin environment, supporting the notion of the northward oceanic subduction during the early Paleozoic. In conclusion, our study provides valuable insights into the composition and deposition history of the Changjiaoba group in the South Qinling belt, contributing to our understanding of the regional geology.