LAUSR

Abstract The Jiao–Liao–Ji belt (JLJB) of the North China Craton is commonly regarded to have been involved in the global-scale collisional events that led to the amalgamation of the Columbia/Nuna supercontinent during the late Paleoproterozoic. Previous studies have revealed that the JLJB underwent a high-pressure granulite-facies metamorphic event with a clockwise P–T–t path during ca. 1.95–1.90 Ga. However, few studies have examined the contemporaneous magmatism and its genetic relationship to the high-pressure granulite-facies metamorphism. In addition, the petrogenesis of the ca. 1.95–1.90 Ga magmatism and its possible constraints on the crustal-thickening process are poorly understood. Our field investigations have discovered a series of late Paleoproterozoic granitoid plutons in Liaodong Peninsula, including the Fangjiawei, Qingchengzi, Songshugou, and Shizijie plutons. Systematic analyses of geochronology, petrology, and geochemistry were conducted to constrain the formation ages, petrogenesis, and tectonic environment of these granites. Zircon U–Pb dating reveals that the granites formed during ca. 1.95–1.88 Ga, coeval with the timing of the regional prograde or peak metamorphism and collision in the JLJB. They show geochemical characteristics of typical adakites, including high Sr (393–860 ppm) contents, low Y (1.03–3.30 ppm) and Yb (0.09–0.27 ppm) contents, and relatively high Sr/Y (125–832) and LaN/YbN (9.34–33.6) ratios. Low MgO, Cr, and Ni contents and the existence of ca. 2.5–2.0 Ga inherited zircons with ancient TDM2 ages indicate that the parental magmas were generated from partial melting of a thickened lower crust. The positive correlation between Dy/Yb and La/Yb ratios and the relatively low Nb/Ta (5.1–18.9, average of 13.6) ratios all suggest that garnets, rather than amphiboles or rutiles, were the dominant phase in the residual source, indicating a melting depth of 30–50 km. Our new results, combined with previous findings, support a rifting-and-collision model whereby the JLJB underwent a transformation from early intracontinental rifting to subsequent opening and closure of an incipient ocean, with the final collision between the Longgang Block and Nangrim Block occurring at ca. 1.95–1.88 Ga with substantial crustal thickening.