| Abstract: | The volcanic rocks of the Xiong'er Group are situated in the southern margin of the North China Craton (NCC). Research on the Xiong'er Group is important to understand the tectonic evolution of the NCC and the Columbia supercontinent during the Paleoproterozoic. In this study, to constrain the age of the Xiong'er volcanic rocks and identify its tectonic environment, we report zircon LA-ICP-MS data with Hf isotope, whole-rock major and trace element compositions and Sr–Nd–Pb–Hf isotopes of the volcanic rocks of the Xiong'er Group. The Xiong'er volcanic rocks mainly consist of basaltic andesite, andesite, dacite and rhyolite, with minor basalt. Our new sets of data combined with those from previous studies indicate that Xiong'er volcanism should have lasted from 1827 Ma to 1746 Ma as the major phase of the volcanism. These volcanics have extremely low MgO, Cr and Ni contents, are enriched in LREEs and LILEs but depleted in HFSEs (Nb, Ta, and Ti), similar to arc-related volcanic rocks. They are characterized by negative zircon εHf(t) values of ?17.4 to ?8.8, whole-rock initial 87Sr/86Sr values of 0.7023 to 0.7177 and εNd(t) values of ?10.9 to ?6.4, and Pb isotopes (206Pb/204Pb = 14.366–16.431, 207Pb/204Pb = 15.106–15.371, 208Pb/204Pb = 32.455–37.422). The available elemental and Sr–Nd–Pb–Hf isotope data suggest that the Xiong'er volcanic rocks were sourced from a mantle contaminated by continental crust. The volcanic rocks of the Xiong'er Group might have been generated by high-degree partial melting of a lithospheric mantle that was originally modified by oceanic subduction in the Archean. Thus, we suggest that the subduction-modified lithospheric mantle occurred in an extensional setting during the breakup of the Columbia supercontinent in the Late Paleoproterozoic, rather than in an arc setting. |
