Zircon U-Pb age, geochemistry and Sr-Nd-Hf isotopic geochemistry of the intermediate-acid rocks from the Heishan-Mulonggou area in the southern margin of North China Block
Zircon U-Pb LA-ICPMS dating for the Xiaxie and Mulonggou granitoid plutons from the southern margin of the North China block yield 154±2Ma (2σ, N=16) and 151±1Ma (2σ, N=15), respectively. These granitoids are metaluminous or weakly peraluminous and high-K calc-alkaline or shoshonite series with A/CNK=0.75～1.04, Na2O+K2O=6.15%～8.42%, K2O/Na2O=0.77～2.29. They are riched in LILE, e.g. LREE, Rb, Ba, K, Pb, Sr and depleted in HFSE, e.g. HREE, Zr, Hf, Ta, Nb, P, Ti with weak negative abnormal of Eu (δEu=0.85～0.99). Whole rocks Sr-Nd compositions of the granitoids are characterized by ISr=0.708676～0.711480 and eNd(t)=-22～-16.1 with Nd model ages of 2.37Ga to 2.96Ga. The granitoids show a large variation in zircon Hf compositions with eHf(t)=-27.8～-18.4 and two-stage model ages of 2.37Ga to 2.96Ga. Geochemistry and Sr-Nd-Hf isotopic compositions of the granitoids suggest that they are derived from an ancient continental crust such as the Archaean Taihua Group, but the zircon Hf compositions and the mafic magmatic enclaves in the granitoids may imply that juvenile component contribute to their formation. Acording to the petrography and regional geological features, the juvenile component are mainly mantle related material. Therefore, the formation of these granitoids could be interpreted as mixing/mingling of an underplated mantle-derived magma and its induced crustal-melted magma in a deep crust.