Paleoproterozoic rifting of the North China Craton: Geochemical and zircon Hf isotopic evidence from the 2137 Ma Huangjinshan A-type granite porphyry in the Wutai area

SHRIMP zircon U-Pb dating of the Huangjinshan granite porphyry in the Wutai area, North China Craton (NCC) yielded concordant ages, with a weighted mean Pb-207/Pb-206 age of 2137 +/- 9 Ma, which indicates that the granite was emplaced in the middle Paleoproterozoic. The granite porphyry is enriched in SiO2, REEs (except Eu), Zr, Nb, Ga, Y and Zn, and depleted in MgO, CaO, Al2O3, Sr, Ba, V, Cr and Ni, with high FeO*/MgO ratios. With the zircon saturation temperatures ranging from 856 to 895 degrees C and a lack on detected inherited zircon, this indicates it is a 'hot' A-type granite, of the type emplaced in anorogenic or extensional settings with high heat flow. Zircons in the granite porphyry have epsilon(Hf)(t) values ranging from -1.72 to +1.84, and Hf model T-DM1 ages of 2429-2554 Ma. The Hf isotopes indicate source of the granites was pre-Neoarchean continental crust mixed with mafic rocks derived from depleted mantle, or directly from the partial melting of ca. 2.5 Ga crust. Given that there are no syn-plutonic gabbro enclaves in the Huangjinshan granite porphyry, it is preferred that it originated mainly from partial melting of ca. 2.5 Ga upper crust without mixing with mantle-derived magma. 2.2-2.0 Ga volcanic and plutonic rocks, which exhibit bimodal magma characteristics emplacing in rifting setting, are abundant in the central NCC. The results presented here are further evidence for that 2.2-2.0 Ga is an important stage of Paleoproterozoic rifting in the central NCC. (C) 2012 Elsevier Ltd. All rights reserved.