Petrology, geochronology, and geochemistry of Paleoproterozoic volcanic rocks in the Xiong’ershan area, NE China: implication for petrogenesis and tectonic setting

The Xiong’er volcanic rocks (XVRs) on the North China Craton (NCC)’s southern margin are vital for understanding the NCC’s late Proterozoic evolution. This study focuses on the Xiong’ershan area’s volcanic rocks and performs detailed investigations on their petrology, chronology, and geochemistry, coupled with re-evaluation of prior geochemical data. Zircon U – Pb dating indicates their eruption ages of 1806–1764 Ma. These volcanic rocks are classified into basic – intermediate and felsic groups. Abundant quartz-filled vesicles and amygdales appear in basic – intermediate volcanic rocks, which can lead to an overestimation of SiO₂ content in geochemical analyses. To remove this bias, the SiO₂ content of the basic – intermediate rocks were re-evaluated by subtracting the quartz contributions from vesicles and amygdales. Our corrected data reveals a clear bimodal distribution (basalt + rhyolite/dacite), contradicting prior interpretations of continuous intermediate compositions. This supports that the XVRs formed in an intracontinental extensional environment, likely to have occurred due to the Columbia supercontinent’s break-up in the late Paleoproterozoic. All volcanic rocks have similar Sr-Nd-Hf isotope ratios and trace element patterns, indicating a common origin. The consistent isotopes and incompatible element ratios imply little crustal contamination during magma ascent. The relationships between MgO and other elements agree with the fractionation of clinopyroxene, olivine, and plagioclase before MgO decreases to ~2 wt%, and then the fractionation of ilmenite and apatite. Additionally, the rocks have lower water content and oxygen fugacity than arc magmas, and contain numerous inherited zircons with ages close to those of the Taihua group’s basement rocks. These results indicate that the XVRs originated from the reworking of the late Paleoproterozoic lithospheric mantle on the NCC’s southern margin, which was enriched by contamination of delaminated lower crust materials and metasomatism of subducted slab fluids before the late Proterozoic.