Trace elements, U-Pb ages and Hf isotopes of zircons from Mesozoic granites in the western Nanling Range, South China: implications for petrogenesis and W-Sn mineralization

The E-W trending Nanling Range, located in the southern part of the South China Block (SCB), is characterized by widespread intra-continental Mesozoic granitoids and accompanying W-Sn polymetallic ore deposits. Detailed studies are presented on trace elements, U-Pb ages and Lu-Hf isotopes in zircons from the Mesozoic A2-type like granitoids (including the Qianlishan, Qitianling, Xianghualing, Huashan, Guposhan, Niumiao, Tong'an, Jinziling and Jinjiling Plutons) from the western Nanling Range. LA-ICP-MS U-Pb analyses of zircon indicate that these granites intruded mainly from ca 160-150Ma. Two types of zircon (magmatic and late-magmatic hydrothermal) with similar ages can be distinguished based on their zircon trace element compositions. The late-magmatic hydrothermal zircons have high contents of metallogenic elements (e.g., W and Sn) and may be closely related with the ore deposits. The ε_Hf(t) values of zircons from the Mesozoic granitoids are mildly negative to positive, indicating the reworking of both old and young crustal components. The significant involvement of Mesozoic juvenile mantle-derived materials in the source can be excluded because of the rare occurrences of mafic rocks with radiogenic isotopic signatures in the area. The average crustal residence age patterns of the Mesozoic granites in the western Nanling Range are similar to those of the Neoproterozoic magmatic rocks in the eastern part of the Jiangnan orogen, which may represent the Neoproterozoic collisional belt between the Yangtze and Cathaysia blocks. Considering the specific isotopic and metallogenic features of the Mesozoic granitoids in the study area, we propose that the western Nanling Range may represent a western extension of Neoproterozoic arc-continent collisional belt in South China. The Mesozoic granitoids of this area may have been generated mainly by reworking of deeply-buried Neoproterozoic arc-related volcanic-sedimentary materials due to thermal perturbations triggered by the subduction of the Paleo-Pacific Plate in Mesozoic time.