Petrogenesis and tectonic implications of Mesoproterozoic granites in the western margin of the North China Craton

The multi-stage anorogenic magmatic events during the Mesoproterozoic era in the North China Craton are of great indicative significance for revealing the breakup process of the Columbia supercontinent. In this study, systematic petrological, zircon U-Pb geochronological, and geochemical investigations were conducted on the Tieqi'angou granite porphyry in the Longxian area, located at the southwestern margin of the North China Craton. By comparing with the research results of coeval granites in the study area, the Mesoproterozoic magmatic activities at the western margin were analyzed and discussed. Zircon dating results show that the U-Pb age of the granite porphyry is 1 794±10 Ma, indicating that it formed in the Mesoproterozoic era and recorded an Early Mesoproterozoic magmatic event. Geochemical characteristics reveal that the Tieqi'angou granite porphyry belongs to shoshonitic alkaline A-type granite, which is enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). It has relatively high Rb/Sr ratios (2.95~3.55) and La/Nb ratios (0.91~8.37), obvious negative Eu anomalies, and low Mg# values. These features suggest that the granite porphyry was derived from crustal melting. Meanwhile, the Sr-Yb elemental characteristics indicate that the granites at the western margin are Nanling-type granites, formed in a relatively shallow crustal region. Comprehensive analysis of the geochemical characteristics of intermediate-basic rocks at the western margin and regional tectonics shows that the igneous rock assemblage at the western margin formed in a post-orogenic intracontinental extensional setting. This assemblage represents the initial geological record of the global breakup process of the Columbia supercontinent in the North China Craton, providing key chronological constraints for the study of the dynamic mechanism of supercontinent breakup.