LA-ICP-MS zircon U-Pb age and geochemical characteristics of Nanyue granites in Hunan Province

Abstract: Located in Hengshan of Hunan Province, Nanyue complex pluton intruded in the Neoproterozoic Lengjiaxi Group. The LA-ICP MS zircon U-Pb ages indicate that the main pluton was formed in the Triassic with a weighted mean age of 215.5±1.5 Ma. However, some small granitic plutons were formed in the early Cretaceous with a 206Pb/238U age of 140.6±0.8 Ma. The late Triassic granites are composed of three individual rock units, being mainly fine- and medium-grained porphyritic hornblende biotite monzonitic granite and surbordinately two-mica monzonitic granite. The early Cretaceous granite is two-mica monzonitic granite. The major and trace element analyses show that the late Triassic granites are of the peraluminous high-K calc-alkaline series, while the early Cretaceous granite is of the high-peraluminous high-K calc-alkaline series. The rocks are enriched in large-ion lithophile elements and depleted in high field-strength elements, with the data ∑REE=92.88-296.56 and weak negative Eu anomaly (δEu=0.28-0.87). The Sr-Nd isotope analyses indicate high ISr values (0.7093-0.7189), low εNd values (-8.04--11.38) and high T2DM values (1.63 Ga-1.90 Ga). The results obtained by the authors show that the Nanyue muscovite-bearing peraluminous granitoids were derived from remelting of Precambrian basement, the magma source of late Triassic granites had the mixed mantle and lower crust materials, and the lithogenesis was related to the lithospheric extension after the orogenesis.