Petrogenesis and tectonic implications of the 2.1–2.0 Ga granitoids in Fuping Complex, North China Craton: Constraints from petrology, geochemistry and zircon U-Pb-Hf isotopes

Abstract

Mid-Paleoproterozoic (2.2–2.0 Ga) magmatism in the Trans-North China Orogen (TNCO) is of great significance for the Paleoproterozoic geological evolution of the entire North China Craton (NCC). In this paper, we present geochemical, SHRIMP zircon U-Pb and Hf isotopic data on the 2.1–2.0 Ga granitoids in the Fuping Complex of the TNCO. These include the Nanying granitic gneiss, which yielded ages of 2075 ± 13 Ma, 2079 ± 9 Ma and 2073 ± 10 Ma, the Gangnan granitic gneiss, dated at 2081 ± 8 Ma, 2082 ± 14 Ma and 2063 ± 7 Ma, the Baiyangling granite with ages of 2077 ± 6 Ma, 2070 ± 19 Ma and 2069 ± 12 Ma, and the Shangzhuang granite, which yielded ages of 2072 ± 12 Ma and 2070 ± 12 Ma. The 2.1–2.0 Ga granitic rocks in Fuping Complex are enriched in SiO2, K2O + Na2O, rare earth elements (REEs) (except Eu), high field strength elements like Zr, Nb, Ga and Y, and depleted in CaO, Al2O3 and Sr. Their Ga/Al ratios and absolute Zr + Nb + Y + Ce contents are high and their average Zr saturation temperatures are as high as 890 °C, all of which are consistent with the features of A-type granite. The εHf(t) values of zircon in all samples are much lower than that of the depleted mantle at the same stage, while Hf model TDM1, TDMC ages have ranges of 2.3–2.7 Ga and 2.4–2.9 Ga, respectively, which are much older than the age of the granitoids. These zircon Hf model ages are similar to those of the Neoarchean TTG (Tonalite-Trondhjemite-Granodiorite) gneisses in the Fuping Complex. Therefore, based on a combination of petrology, geochemistry and isotopic characteristics, we infer that these four 2.1–2.0 Ga granitic plutons in the Fuping Complex are partial melts of the Neoarchean TTG gneiss generated in an extensional environment. Based on extensive data, the 2.1–2.0 Ga A-type granites and the mafic dikes in the Fuping Complex represent a bimodal magma association. Considering the sedimentary rocks of the Gantaohe Group, deposited in the same period, we deduce that the 2.1–2.0 Ga A-type granite in the TNCO Fuping Complex was emplaced in an intra-continental rift setting in the NCC. This evidence indicates that the North China Craton was initially stabilized at the end of the Neoarchean.