Petrogenesis of the Maixie Pluton in Northwest Jiangxi Province:Constraints from Petrochemistry,Zircon U-Pb Chronology and Hf Isotope

In this paper,two representative samples of Maixie pluton were selected for LA-ICP-MS zircon U-Pb dating,yielding U-Pb ages of(434±2)Ma and(437±2)Ma,which indicates that the Maixie granites were formed in Caledonian orogen.Whole-rock geochemical data indicate that the rocks belong to high-K calc-alkaline series,they are typical metaluminous I-type granite,with some features similar to those of the high Ba-Sr granite,i.e.,high content of Ba and Sr and high ratios of Sr/Y and La/Yb,but low content of Y(19 μg/g) and Yb(1.8 μg/g) and low ratios of K/Rb and Rb/Sr(average 0.37).Besides,the rocks show negative Eu anomaly,and are depleted in high field strength elements,such as Nb,P,Ti and so on.The Hf isotopic compositions of zircons show that the rocks have eHf(t) values of-35.32 to-1.50 and T2DM(Hf) model ages ranging from 3.63 to 1.51 Ga,implying that the magma was derived from Paleo-or Meso-Proterozoic rocks,with involvement of some jurenile mantle in petrogenesis.Combined with the geochemical composition,the inhomogenous zircon Hf isotopic compositions as well as the appearance of common mafic microgranular enclaves,we suggest that the Maixie pluton were formed by magma mixing between the mafic magmas and felsic magmas generated by partial melting of overlying lower crust inducing mafic magmas.