Petrogenesis of the Late Cretaceous Jiepailing Granitoids in South China: Implications for Sn Mineralization and Tectonic Evolution

Abstract

The Late Cretaceous Jiepailing granitoids, located at the central Nanling Range in South China, are closely associated with significant Sn-Li-Be-F polymetallic metallogeny. The Jiepailing granitoids mainly consist of granitic porphyry and zinnwaldite granite. The two granitoids have an A-type affinity, showing elevated Rb/Sr ratios and significant depletions in Ba, Sr and P. Integrated zircon and monazite U-Pb dating results suggest that granitic porphyry and zinnwaldite granite were emplaced at ~89 Ma and ~94 Ma, respectively. The low Ce⁴⁺/Ce³⁺ ratios of the Jiepailing granitoids, together with significant negative Eu anomalies of the zircons, indicate that their formation occurred under conditions of reduced oxygen fugacity. Through the analysis of zircon Hf-O and whole-rock Nd isotopes, it has been determined that both stages of the Jiepailing granitoids originated in the lower-middle Mesoproterozoic crustal basement [ε_Nd(t) = –5.33 to –4.96, t^C_DM(Nd) = 1289–1234 Ma, ε_Hf(t) = –4.13 to +2.22, t^C_DM(Hf) = 1418–1015 Ma and δ¹⁸O_Zrc = 6.33‰–7.72‰], with the involvement of mantle-derived materials. Both granitic porphyry and zinnwaldite granite exhibit elevated concentrations of fluorine (F), with the positive correlation between F and Sn emphasizing the crucial role of high F sources in tin mineralization. Drawing upon the study of the Late Cretaceous magma systems in southern Hunan and through comparison with the mineralized granites observed in coastal regions during the Late Cretaceous, a genetic model for the mineralized granites in the Nanling region is developed. When the Paleo-Pacific Plate retreated to the coastal region, the continental crust in southern China underwent extensional thinning and asthenospheric upwelling due to gravitational collapse. Such processes resulted in the partial melting of the middle–lower crustal metamorphic sedimentary basement and the subsequent formation of F-rich granitic magmas, related to tin mineralization.