Early–Middle Permian plutons in the Langshan area, western Inner Mongolia, China, and their tectonic implications

Whether the southward subduction of the Paleo-Asian Ocean (PAO) beneath the northern North China Craton (NCC) was still on-going during Permian is a key issue for understanding the tectonic evolution of the southeastern Central Asian Orogenic Belt (Xing'an–Mongolia Orogenic Belt), and the voluminous Permian plutons distributed along the northern margin of the NCC can provide important insights into this controversy. New LA-ICP-MS zircon U–Pb ages from 4 basic, 6 intermediate and 11 acidic plutons in the Langshan area in northwestern NCC indicate that the plutons were formed during the Early–Middle Permian (290–265 Ma). Four basic diorites show affinities with continental basalts and probably crystallized from mantle-derived melts, whereas the intermediate and most acidic plutons are calc-alkaline I-type granitoids and four acidic plutons have the features of aluminous A2-type granites, and all of them probably originated from partial melting of various crustal materials. The Early–Middle Permian plutons and coeval bimodal volcanic rocks and continental basaltic intrusions occur together in both the northern NCC and adjacent Xing'an–Mongolia Orogenic Belt, implying a uniform extensional setting at that time. In addition to the intense magmatism, the regional extension also resulted in the development of a Red Sea-like limited oceanic basin within the Xing'an–Mongolia Orogenic Belt, and its subsequent closure may have created the Solonker suture. Such a tectonic scenario is in agreement with the Late Permian–Early Triassic blueschist-facies metamorphism induced by warm subduction of young oceanic slabs, Permian stratigraphic and paleontological data, and paleomagnetic record.