Meso–Neoproterozoic rift system along the southwestern North China Craton: evidence from recent drilling and seismic data

It is widely accepted that three Meso–Neoproterozoic rift systems exist within the North China Craton (NCC): Xiong’er Rift System, Zhaertai-Bayan Obo Rift System, and Yanliao Rift System. However, the presence of an additional rift system on the southwestern margin of the NCC has long been debated, primarily because volcanic rocks have not been identified in outcrops. To address this gap, we conducted geochronological, geochemical, and stratigraphic investigations using drilling cores from the Pantan 1 well together with a regional two-dimensional seismic profile. Moreover, by comparing the lithology of the Xiong’er Group in the Mesoproterozoic Changcheng System of the Xiong’er Rift System, we reconstructed a Mesoproterozoic sedimentary – volcanic stratigraphic sequence for the southwestern margin of the NCC. Therefore, this study proposes the existence of a fourth Meso–Neoproterozoic rift, here referred to as the Guyuan Rift, located along the southwestern margin of the NCC. This rift is distinguished by a unique lithological assemblage that includes volcanic rocks such as basaltic andesite and diabase. The U–Pb ages of the basaltic andesite are 1768.51 ± 0.39 Ma and 1778.70 ± 8.0 Ma. These values correspond to the U–Pb age of 1772.50 ± 4.9 Ma obtained for volcanic rocks in the upper part of the Xiong’er Group in the Zhongtiao Mountains. In addition, the U–Pb age of the diabase is 813.5 ± 7 Ma. The basaltic andesite appears as a wave-impedance layer in the deep seismic reflection profile. The geochemical characteristics of both the basaltic andesite and the diabase dykes indicate that continental rift basins formed along the southwestern margin of the NCC during the Early Mesoproterozoic and Neoproterozoic. Taken together, these findings support the existence of a Meso–Neoproterozoic rift system on the southwestern margin of the NCC. They also provide new evidence for reconstructing the tectonic framework of the NCC during this interval.