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

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 degrees C, all of which are consistent with the features of A-type granite. The epsilon(Hf)(t) values of zircon in all samples are much lower than that of the depleted mantle at the same stage, while Hf model T-DM1, T-DM(C) 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.