Geochemical and Sr-Nd isotopic mapping of source provinces for the Mawson charnockites, east Antarctica: implications for Proterozoic tectonics and Gondwana reconstruction

Large charnockite plutons (similar to 970 Ma) were intruded into high-grade metamorphic rocks of the Mawson Coast area, east Antarctica, immediately after peak granulite metamorphism in the region. Detailed Sr-Nd isotopic studies suggest that charnockites in the central zone have significantly higher initial Sr-87/Sr-86 ratios (0.7205-0.7334), lower initial epsilon(Nd) values (-8.8 to -11.1) and older Nd depleted mantle model ages (T-DM(Nd)) (2.03-2.16 Ga) than those from the western and eastern zones (0.7076-0.7263; -4.0 to -8.4; 1.68-1.96 Ga, respectively). The isotopic compositions of the country rocks also mimic such regional variations. Apart from the isotopic variations, the charnockites can also be divided into two major geochemically distinctive categories, i.e. high-and low-Ti groups, with-the high-Ti group being characterized by higher TiO2, P2O5, K2O, FeO*, Na2O + K2O, Zr, Nb, Y, La, Ce, Rb, Pa, Rb/Sr and Ga-Al and lower MgO, CaO, Al2O3, Na2O, Mg#, Cr and Ni than the low-Ti group. However, the two groups show no obvious difference in terms of Sr-Nd isotopic signatures. Compared with Palaeozoic I-type granites from the Lachlan Foldbelt, both groups of charnockites are generally higher in TiO2, P2O5, K2O, Zr, Nb, Y, La, Ce and Ba, and lower in MgO, CaO, Sr/Ba and Mg#, with the low-Ti charnockites being somewhat transitional between the high-Ti charnockites and I-type granites. On the spiderdiagram, both charnockites and I-type granites show similar degrees of negative Nb anomaly, implying derivation from similar Nb-depleted sources