Petrogenesis and tectonic implications of the charnockites in the Yishui Terrane, North China Craton

Abstract

A combined study of zircon U-Pb ages, Lu-Hf isotopes and whole-rock geochemistry was carried out for representative charnockites from the Yishui terrane in the Western Shandong Province, NCC. The results demonstrate that the charnockites in the Yishui terrane are of igneous origin rather than derivation from remelting or metamorphism of supracrustal rocks. Zircon U-Pb dating for the charnockites in the Yishui terrane indicates protolith emplacement around 2.52–2.56Ga and synchronous metamorphism around 2.50–2.53Ga. Zircon Lu-Hf isotopes analyses show that the charnockites have positive εHf(t) values with an average +4.03, and depleted mantle two-stage zircon Hf model ages (TDM2) mainly cluster around 2.7–3.0Ga, indicative of a source of juvenile crust formed around 2.7–3.0Ga. Furthermore, the charnockites with <70% wt% SiO2 tend to be magnesian calcic to calc-alkalic and metaluminous, only a small population of the charnockites with >70wt% SiO2 are ferroan alkali-calcic and weakly peraluminous, which are consistent with geochemical features of Cordilleran-type granitoids, suggesting a deeply eroded magmatic arc derived from remelting of juvenile crust mainly formed around 2.7–3.0Ga. Taken the comprehensives of available whole-rock geochemical and Zircon Lu-Hf isotopic data of the charnockites, synchronous emplacement and metamorphism, high-temperature setting of charnockites, granulite-facies metamorphism of anticlockwise P-T path in the Yishui terrane as well as the whole NCC, we conclude that the combined geodynamics of mantle plume and oceanic crust subduction might contribute to the formation of the charnockites in the Yishui terrane as well as similar late Archean charnockites in other areas of the NCC, further implying extensive occurrences of modern-style plate tectonic accretions in late Archean in the NCC.