The Neoproterozoic S‐Type Granites in the Western Jiangnan Orogen: Petrogenetic and Geodynamic Implications

ABSTRACT The mid‐Neoproterozoic tectonic evolution of the western Jiangnan Orogen in the context of the Rodinia supercontinent remains unresolved due to debates regarding the interpretation of the petrogenesis of igneous rocks. In this study, we present an integrated dataset of petrology, whole‐rock geochemistry, zircon U‐Pb ages, and Hf isotopes for granitic samples from the Fanjingshan area in the western Jiangnan Orogen. LA‐ICP‐MS zircon U‐Pb dating indicates that they crystallised ca. 810 Ma. Whole‐rock geochemical data demonstrate that they exhibit typical features of S‐type granites and were derived from dehydration melting of a metasedimentary protolith. Zircon ε Hf ( t ) values range from −7.9 to 1.6, with a main peak value of −3.5. Two‐stage Hf model ages of 1.5–1.9 Ga suggest that these granites were derived from ancient crustal materials. Extensive fractional crystallisation and magmatic–hydrothermal interactions are inferred from low rare earth element (REE) contents, low Nb/Ta and Zr/Hf ratios, and a distinct REE tetrad effect. Combined with coeval arc‐related magmatism and rift basins, the Fanjingshan granites were most likely emplaced in a back‐arc setting. Available data indicate that rift basins occurred extensively at the periphery of the Yangtze Block ca. 810 Ga, implying their involvement in the breakup of the Rodinia supercontinent.