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

Abstract

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 εNd(t) values of −5.7 to −0.8 with two-stage Nd model ages of 2.99–2.63 Ga and zircon εHf(t) values of −7.3 to −2.9 with two-stage Hf model ages (TDM2(Hf)) of 2.94–2.61 Ga. These TDM2(Hf) ages are similar to those of ∼ 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.