Petrogenesis and implications of similar to 2.1 Ga Jingqishan granites in the Jiaobei Terrane, North China Craton

Widely distributed 2.2-2.1 Ga A-type granites in the North China Craton (NCC) have not only a significant role in unveiling the regional Palaeoproterozoic tectonic evolution but also crucial implications for the spatial and temporal evolution of A-type granite. This paper presents zircon U-Pb dating, geochemistry and Nd and Hf isotopes of Jingqishan Palaeoproterozoic gneissic granites from the Jiao-Liao-Ji Belt (JLJB) of the eastern NCC. The Jingqishan granites are mainly monzogranites. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb analyses of three samples yield concordant ages of 2124 +/- 7 Ma, 2089 +/- 11 Ma and 2088 +/- 10 Ma. The Jingqishan granites are ferroan, calc-alkalic to alkali-calcic, and metaluminous-peraluminous. The high Ga/Al ratios, Zr + Nb + Y + Ce contents and Zr saturation temperatures (861 C on average) of these granites are consistent with the features of A-type granite. The granites have epsilon Nd(t) values of-5.7 to-0.8 with two-stage Nd model ages of 2.99-2.63 Ga and zircon epsilon Hf(t) values of-7.3 to-2.9 with two-stage Hf model ages (T-DM2(Hf)) of 2.94-2.61 Ga. These T-DM2(Hf) ages are similar to those of similar to 2.5 Ga Jiaobei Tonalite-Trondhjemite Granodiorite (TTG) gneisses. Based on petrology, geochemistry and isotopic characteristics, we infer that the Jingqishan A-type granites are mainly partial melts of the Jiaobei 2.5 Ga TTGs. Combining our data with those published for 2.2-2.1 Ga JLJB granites and extensive data, we discover that both 2.1 Ga and 2.18 Ga A-type granites of the JLJB have A2-type granite characteristics and formed in a back-arc basin but were generated from the partial melting of different sources at two magmatic stages. Most 2.2-2.1 Ga A-type granites of the NCC belong to A2-type that sourced from late Achaean crustal rocks in an extensional setting.