Petrogenesis of Late Jurassic Pb–Zn mineralized high δ18O granodiorites in the western Nanling Range, South China

Abstract

Amphibole-bearing granites are commonly considered to be I-type granites, derived by partial melting of igneous rocks. However, the contribution of sedimentary rocks to the source of such rocks is difficult to identify and remains debated. Here, we present a study of amphibole-bearing Pb-Zn mineralized granodiorites in the western Nanling Range of South China. LA–ICP–MS zircon U–Pb ages show that these granodiorites were generated during the Late Jurassic (ca. 161 Ma). They have variable SiO2 contents of 61.8–70.7 wt% and have high-K or shoshonitic characteristics, with varied Mg# (0.28–0.54). These granodiorites are enriched in Th and U, and depleted in Nb, Ta and Ti. They display enriched light rare earth element (LREE) and flat heavy rare earth element (HREE) patterns, with slightly negative to negligible Eu anomalies (δEu = 0.74–0.95). Given their high zircon δ18O values (8.8‰–11.9‰), as well as negative εNd(t) (−7.5 to −5.1) and zircon εHf(t) (−13.9 to −7.5) values, we suggest that these Pb-Zn mineralized granodiorites in the western Nanling Range were derived mainly by partial melting of Middle Neoproterozoic mafic volcaniclastic rocks from the Nanhua rift basin, South China, in the lower crust. This study provides an important insight into the genesis of amphibole-bearing granites. We suggest that the partial melting of crustal metasedimentary and metaigneous rocks is an important mechanism for the Mesozoic crustal reworking of South China, and granodiorites generated by such a mechanism should also favor Pb–Zn mineralization.