Geochronology and significance of the early Mesoproterozoic tectono-magmatic event in the western segment of the North Qinling Mountains

Two early Mesoproterozoic granite intrusions—the Gongjiangou deformation intrusion in the Taibai batholith and Hudian deformation intrusion in the BaoJi batholith—are for the first time identified in Baoji in the western segment of the North Qinling orogenic belt. Their protoliths are both medium- and fine-grained monzogranite. The authors studied the features of CL images of zircons and analyzed their origin. U-Pb LA-ICPMS dating of zircons yielded magmatic crystalline ages of 1741±12 and 1770±13) Ma. Both petrological and geochemical data show that: the deformation intrusions formed in a subduction-collision environment at plate margins and the magma originated by partial melting, which shows that there occurred a strong tectono-magmatic event in the western segment of the North Qinliing orogenic belt in the early Mesoproterozoic. The LA-ICPMS U-Pb dating zircon age (450.5±1.8 Ma) of the Gongjiangou deformation intrusion in Taibai and Hudian deformation intrusion in BaoJi and the age (1765 Ma±8 Ma) of zircons captured in the Honghuapu tonalite in Fengxian, Shaanxi, provide a basis for defining the time range of the early Mesoproterozoic Lüliangian tectono-magmatic event in the western segment of the North Qinling (~1.8 Ga). Based on an analysis of the tectonic attribute of the western segment of the North Qinling orogenic belt, the authors suggest that the nearly 1.8 Ga tectono-magmatic event might be the response of the convergence of the supercontinent Columbia in the western segment of the North Qinling orogenic belt.