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• A dolerite sill emplaced into the Guanmenshan Formation was dated at ca. 2060 Ma. • The lower part of Fanhe Group was deposited in the span of 2200–2060 Ma in the Rhyacian Period. • The lower part of Fanhe Group provides excellent stratigraphic records of the GOE and LJE in the NCC. The Great Oxidation Event (GOE) and Lomagundi-Jatuli Event (LJE) during Paleoprterozoic Era represent significant global environmental changes in Earth's history and their geological records have been identified from many ancient cratons. However, reliable records of GOE and LJE are rare in the North China Craton (NCC) due to high-grade metamorphism on Paleoproterozoic strata during Orosirian Period and poor age constraints. Weakly metamorphosed to unmetamorphosed Proterozoic strata termed as Fanhe Group of around 8 km thick are well preserved in Fanhe Basin in the Archean Longgang Block in northeastern NCC and the Guanmenshan Formation from the lower part of the Fanhe Group is characterized by positive δ 13C carb excursion of around +5‰. Since the Fanhe Group was usually considered as Meso-Neoproterozoic in ages, the reasons for positive δ 13C carb excursions in the lower Fanhe Group are unclear. Our new LA-(MC-)ICP-MS U-Pb dating on a dolerite sill intruding into the Guanmenshan Formation yields two upper intercept 207Pb/206Pb ages of 2065 ± 20 Ma (95% confidence, MSWD = 1.4, N = 26) and 2062 ± 22 Ma (95% confidence, MSWD = 1.05, N = 22), respectively. Combined with the weighted mean 207Pb/206Pb age of the youngest detrital zircon population of the Daposhan Formation (2199 ± 19 Ma, 95% confidence, N = 8, MSWD = 0.47) and their contact relations, the deposition ages of the Daposhan, Kangzhaungzi, Guanmenshan and Tongjiajie formations from the lower part of Fanhe Group were constrained to be Rhyacian Period from ca. 2200 Ma to ca. 2060 Ma, not Mesoproterozoic Era as previously regarded. These new age constraints provide solid evidence for the existence of weakly metamorphosed stratigraphic records of GOE and LJE in lower part of Fanhe Group in the NCC. Stratigraphic correlations with other ancient cratons show that the Guanmenshan Formation in Fanhe Basin in the northeastern NCC can be correlated with the Dashiling Formation of the Hutuo Group in the central NCC, the Lucknow Formation in West Australia, the Upper Pretoria Formation in South Africa, the Gordon Lake Formation in North America and the Tulomozero and Kuetsjärvi formations in Fennoscandia, and therefore the Fanhe Group provides excellent stratigraphic records to study GOE and LJE in the NCC. [ABSTRACT FROM AUTHOR]

• Identification of the ca. 1.23–1.21 Ga dolerite sills and flood basalts from Fanhe Basin in the northeastern North China Craton. • The ca. 1.23–1.21 Ga mafic rocks can be divided into alkaline and sub-alkaline series and exhibit distinct trace element and Nd isotopic compositions. • The alkaline rocks were derived from an OIB-like asthenospheric mantle source. • The sub-alkaline rocks were derived from a subduction-modified subcontinental lithospheric mantle. The Ectasion Period (1400–1200 Ma) represents a transition stage from Columbia (Nuna) to Rodinia supercontinents. LIPs and mafic magmatic events during this period can provide important constraints on deep processes and paleogeographic reconstructions during this transition. In this paper, we firstly reported some ca. 1.23–1.21 Ga flood basalts coeval with mafic sills from the Fanhe Basin in the northeastern North China Craton (NCC). New zircon/baddeleyite U-Pb/Pb-Pb dating on dolerite sills emplaced into the Fanhe Group yields emplacement ages from 1231 ± 9 Ma to 1206 ± 20 Ma. Whole-rock 40Ar/39Ar dating of two basalts from the Erdaogou Formation yields approximate total gas ages of ca. 1250 Ma and ca. 1210 Ma. These new geochronological results revealed that the Erdaogou basalts are coeval with some dolerite sills emplaced into the Kuangzhuangzi, Guanmenshan and Tongjiajie Formations and the dolerite sills emplaced into the Hutouling and Erdaogou Formations. These newly recognized ca. 1.23–1.21 Ga mafic rocks can be linked to the broader Licheng LIP of the previous studies. The ca. 1.23–1.21 Ga mafic rocks in the Fanhe basin can be divided into alkaline and sub-alkaline series and these two series exhibit distinct trace element and Nd isotopic compositions. The alkaline rocks show strongly fractionated chondrite-normalized REE patterns with high La N /Yb N values of 12.69–15.05. The sub-alkaline samples display less fractionated REE patterns with lower La N /Yb N values of 2.74–10.13. The alkaline rocks have OIB-like trace element patterns and slightly negative to positive ε Nd (t) values from −0.7 to 0.7. An OIB-like, asthenospheric mantle source is suggested as the source of the alkaline rocks. In contrast, the sub-alkaline rocks exhibit low negative ε Nd (t) values from −10.9 to −4.6 and are interpreted to be derived from a subduction-modified subcontinental lithospheric mantle. By comparisons with the coeval mafic magmatism in other parts of the NCC and other cratons, we suggest that the ca. 1.23–1.21 Ga mafic magmatism or LIP in the NCC was either related to the mantle plume that resulted in the Marnda Moorn LIP in Western Australia or related to a back-arc extension prior to the formation of a Grenvillian orogen located in another continent connected to the southeastern margin of the NCC during assembly of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]