A Calymmian anchor point for the northern fringe of the North China Craton: Constraints from SHRIMP U–Pb geochronology of the Sailinhudong Group in the Bayan Obo Area, Inner Mongolia

Abstract

The North China Craton (NCC), confined by a series of late Paleoproterozoic–Neoproterozoic extensional basins, is likely a key piece in welding the supercontinent Columbia. The debate regarding the connection between the northern NCC and either the North Australia Craton or the Siberia Craton is essential for understanding the assemblage and break-up of Columbia. The northern marginal rift system (NMRS) of the NCC is an ideal region in which imprints related to neighboring cratons could be preserved. However, the absence of a well-calibrated chronologic framework obstructs subregional attribution and regional correlation and obscures the tectothermal reconstruction of the Proterozoic NMRS, although the zircon U–Pb ages of the volcanic interbeds and crosscutting dykes were sporadically obtained from the Bayan Obo, Zha’ertai, Huade, Shi’nagan and Langshan groups. This study presents two SHRIMP U–Pb ages constraining the Sailinhudong Group (SG) in Darhan–Muminggan Joint Banner to the early Mesoproterozoic (probably the early Calymmian), including one zircon U–Pb age of ca. 1.58 Ga from a volcanic interbed and the other baddeleyite Pb–Pb age of ca. 1.31 Ga from a crosscutting gabbro–diorite dyke. Zircon Hf isotopic compositions of the ca. 1.58 Ga tuff layer in the volcanic–seismic succession from the lower SG are all depleted, similar to those of the ca. 1.58 Ga tuffite layer overlying the seismic succession in the third member of the Gaoyuzhuang Formation in the Yanliao Rift. In conjunction with previous studies, we propose an external origin for the tuff layers and associating seismic successions. A ca. 1.58 Ga catastrophic eruption is inferred to have transmitted substantial tephra and emanated considerable energy to the northern NCC. The ca. 1.58 Ga catastrophic event is considered an anchoring point for attributing and correlating the Calymmian successions through the northern NCC. According to the latest lithostratigraphic and chronostratigraphic advances, the late Paleoproterozoic–Neoproterozoic successions outcropping in the NMRS are further subdivided into the Statherian (the Zha’ertai Group and lower parts of the Bayan Obo and Huade groups), Calymmian (the Sailinhudong, Shi’nagan and middle parts of the Bayan Obo and Huade groups) and Tonian (the northern Langshan Group).