Chronostratigraphic Framework for the Mid-Proterozoic in the Northern Margin of the North China Craton

Recent significant advances have been achieved in supercontinent-reconstruction, metallogenic prospection, and coevolution between early-life and environment through probing the Mid-Proterozoic volcanic-sedimentary formations and intrusive magmatic rocks. Comparing with the others, the Mid-Proterozoic cover sequence exposed in the northern North China Craton (NCC) is the most profoundly studied, since it preserves the most successive depositional sequences, hosts the largest REE-Nb-Fe ore deposit, and documents a potential causal link between the advent of multicellular eukaryote and several conspicuous intervals of atmospheric oxidation. It is generally accepted that the Mid-Proterozoic sedimentary successions in the northern NCC are confined by two major rift systems, including the Yanliao Rift and the Northern Marginal Rift System (NMRS). Benefiting from a series of high-quality age constraints from the newly identified tuffite beds and mafic intrusions, the Mid-Proterozoic in the Yanliao Rift is well-subdivided to Changchengian (Statherian), Jixianian (Calymmian) and Undefined System (partly Ectasian, 1.4-1.32 Ga). However, a similar chronostratigraphic chart with robust age constraints for the NMRS remains elusive since 1990’s. In traditional lithostratigraphic schemes, the Mid-Proterozoic strata of the NMRS are divided into the Langshan Group in the west, the Zha’ertai, Bayan Obo, Shi’nagan and Sailinhudong groups in the central part, and the Huade Group in the east. Over the past decades, several sporadic tuffite beds have been documented at different locations and stratigraphic horizons across Mid-Proterozoic NMRS. Our latest research on the event stratigraphy and chronostratigraphy of the Sailinhudong Group further anchors a reliable benchmark for the Calymmian throughout the NMRS and the northern NCC as well, implicating a drastic eruption at ca. 1.58 Ga which transmitted tremendous energy and massive tephra to the northern NCC. Furthermore, we have recently obtained a zircon U-Pb age at ca. 1.7 Ga from a granitic vein intruding to the lower Zha’ertai Group, indicating that initiation of the Mid-Proterozoic accumulation in the NMRS should predate that in the Yanliao Rift. According to a combination of the lithostratigraphic advances, dating results from the volcanic interbeds and detrital zircon age archives, we present an updated regional correlation framework for the Mid-Proterozoic of the NMRS: (a) the Zha’ertai Group and the lower parts of the Bayan Obo and Huade groups are attributed to the Statherian; (b) the Sailinhudong, Shanheila and middle parts of the Bayan Obo and Huade groups correspond to the Calymmian; (c) the Langshan Group in the northern Langshan area is attributed to the Tonian; (d) the upper part of the Huade Group is attributed to the Ectasian; and (e) the upper part of the Bayan Obo Group is the most potential unit corresponding to the Tonian in the northern NCC. This study was supported by the National Natural Science Foundation of China (Grant Nos. U2444209, U2444210 and 41902197).