Mesoproterozoic (∼1.3 Ga) S–type granites in Shangdu area, Inner Mongolia of the North China Craton (NCC): Implications for breakup of the NCC from the Columbia supercontinent

Abstract

Mesoproterozoic (∼1.3 Ga) magmatism in the North China Craton (NCC) was characterized by diabase sills, while contemporary granitic magmatism was relatively rare, limiting our understanding of the NCC’s evolution during this period. In this manuscript, we report newly identified ∼1.3 Ga S–type granitic plutons in the Shangdu area, the western part of the northern NCC. Based on the results of geochemical, geochronological and zircon in–situ Lu–Hf isotope analyses, we discussed the petrogenesis, tectonic setting of the granitic plutons and the regime that drove the break–up of the NCC from the Columbia supercontinent. The zircon laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating results indicate that these granites were emplaced at some time between 1315 ± 21 Ma and 1307 ± 32 Ma. Moreover, the geochemical results show that they have high contents of SiO2 (75.34–76.97 wt%), Al2O3 (12.90–13.61 wt%) and Na2O + K2O (6.21–8.31 wt%), but low MgO (0.09–0.25 wt%) and Mg# (14–34). The A/CNK ratios varied between 1.10 and 1.28, indicating that the granites belong to the peraluminous series. Furthermore, the existence of Al–rich minerals (e.g., muscovite and garnet) suggests that they are the S–type granites. The ∼1.3 Ga zircon display negative to slightly positive εHf(t) values (−9.28–3.1) and old two–stage model ages (TDM2) (3.3–2.1 Ga). The ages of the inherited zircon and Lu–Hf isotope compositions of the ∼1.3 Ga zircon in the granite are consistent with those of the detrital zircon from Jining complex, the eastern part of the Khondalite Belt. Based on these facts, we infer that the granites in this study derived from the partial melting of the Jining complex. The coeval mafic dykes (in the Yanliao large igneous province) and the Shangdu granite in the north margin of the NCC strongly suggest an extensional setting, which was related to the break–up of the NCC from the Columbia supercontinent. A mantle plume was likely the dominant driver of the break–up and it should have provided heat for the partial melting of Jining complex.