Middle Permian Wuhaolai mafic complex in the northern North China Craton: Constraints on the subduction-related metasomatic mantle and tectonic implication

The Wuhaolai mafic complex is situated at the middle part of the northern margin of the North China Craton (NCC), Inner Mongolia. LA-ICP-MS zircon U-Pb ages, geochemical, and Sr-Nd isotopic data are presented to confirm the formation age of the complex, the nature of Paleozoic lithospheric mantle, and the tectonic evolution of the northern margin of the NCC. The mafic complex is composed of pyroxenite, gabbro, and diorite, which are derived from the same parental magma. The geochronological results show that this mafic complex was emplaced at 265.9 +/- 3.3 Ma. All three different rock types are characterized by calc-alkaline series with enrichment of large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletion of high field strength elements (HFSEs) and high rare earth elements (HREEs), and show negative Nb-Ta anomalies. Besides, they exhibit a low (Sr-87/Sr-86)(i) (0.7059-0.7065) and high epsilon(Nd(t)) (-13.35 to -8.19) values. These geochemical features also indicate that the parental magma of this complex was derived from an EM I-like lithospheric mantle, which has undergone subduction-related metasomatism. Combined with the previous studies on the Late Carboniferous to Late Permian intrusions from the northern margin of the NCC, the Wuhaolai mafic complex belongs to the Within-Plate Basalt, representing a tectonic setting of continental extension environment, and the final closure time of the Paleo-Asian Ocean (PAO) should be earlier than the Middle Permian.