Origin of dyke swarms by mixing of metasomatized subcontinental lithospheric mantle-derived and lower crustal magmas in the Guocheng fault belt, Jiaodong Peninsula, North China Craton

Cretaceous dyke swarms are widespread in the Guocheng fault belt, Jiaodong Peninsula, eastern North China Craton (NCC). Elemental analyses show that these dykes are classified as high-K calc-alkaline to shoshonitic series, and are characterized by high MgO (up to 10.33wt%; Mg-#<69.8), Cr (<571ppm) and Ni (<235ppm) at low silica contents. They are enriched in LILEs (e.g. Sr, Ba, K and Pb) and LREEs, depleted in HFSEs (e.g. Nb-Ta, Zr-Hf, Ti and P), and possess relatively radiogenic Sr (initial Sr-87/Sr-86=0.7078 to 0.7116) and Nd [epsilon(Nd)(t)=-20.8 to -13.5] and much less radiogenic Pb (Pb-206/Pb-204=17.13 to 17.56) isotope signatures. These data, combined with inversely zoned amphibole and pyroxene phenocrysts, suggest a hybrid origin for the Guocheng dykes. The inferred magma evolution is dominated by repeated injection of basic magma from metasomatized subcontinental lithospheric mantle (SCLM) into a lower crustal reservoir of intermediate-felsic composition. This refertilized lithospheric mantle source, probably together with its overlying enriched lower crust, was formed by subduction-related fluid metasomatism in the Palaeoproterozoic, which resulted from final cratonization of the NCC at ca. 1.8Ga during assembly of Columbia supercontinent. Our observations also imply that similar mixed magma system with oxidized and sulphur-rich signatures may be the key to the formation of hydrothermal polymetal deposits and the potential target for mineral exploration in some undiscovered areas. Copyright (c) 2012 John Wiley & Sons, Ltd.