关键词: 大火成岩省, 超大陆重建, 大陆裂谷与裂解, 火成碳酸岩, 稀土成矿事件, 华北克拉通, 哥伦比亚(奴那)超大陆

Abstract: The Yanliao rift zone in the northern North China Craton is associated with the emplacement of large volumes of diabase sills within the Mesoproterozoic Xiamaling, Wumishan, Gaoyuzhuang and Tieling formations. In this study, detailed field investigation and geological cross-section measurements show that the sills are distributed over an area of >1.2×105 km2  with cumulative thickness of 50 to >1800 m. A tabulation of 18 published baddeleyite 207Pb/206Pb ages of diabase emplaced into different lithospheric layers, including the Xiamaling, Wumishan, Gaoyuzhuang and Tieling formations, shows that sill emplacement occurred between 1.33 and 1.30 Ga with a peak age of ca. 1.32 Ga. The Yanliao diabase sills exhibit similar geochemical features of tholeiitic composition with intraplate characteristics. Given its vast areal and volumetric extents and relatively short duration of emplacement, along with the intraplate setting, the diabase sill province of the Yanliao area constitutes a mid-Mesoproterozoic large igneous province (LIP) in the North China Craton, which we named here the Yanliao LIP. Emplacement of the Yanliao LIP was accompanied by pre-magmatic uplift that started at about 1.35 to 1.34 Ga, as indicated by the disconformity between the Changlongshan and Xiamaling formations. Among the globally known LIPs, the Yanliao LIP of the northern North China Craton bears clear similarities to the 13.2 Ga DerimGaliwinku LIP of the North Australian Craton in terms of age, occurrence, petrographical assemblage and geochemical compositions. Moreover, compositions and ages of the late Paleo-Mesoproterozoic stratigraphic units in two cratons are also very similar,  as exemplified by the top stratigraphic horizons that are intruded by the diabase sills and are both dominated by black shales (Xiamaling Formation in Yanliao area and Velkerri Formation of Roper Group in Northern Austarlia). These similarities indicate the two cratons were connected (or close neighbors at least) during the mid-Mesoproterozoic period, and the Yanliao and DerimGaliwinku LIPs are the fragments of the same LIP. Field investigations and zircon Th-Pb dating show that the REE-Nb-rich carbonatites in the Bayan Obo deposit occur mainly as sills emplaced at ca. 1.30 Ga. Zircon morphology and analyses of trace elemental composition and mineral inclusion demonstrate that crystallization of the 1.30 Ga carbonatite sills in the Bayan Obo deposit was accompanied by large-scale REE-Nb mineralization. Therefore, the Bayan Obo carbonatites and REE-Nb deposit are thought to be spatially and temporally linked with the 1.331.30 Ga Yanliao LIP in the northern North China Craton, and their formations were likely related to the continental rifting and breakup of the North China Craton from the Columbia (Nuna) supercontinent.

Key words: Large igneous province (LIP), paleogeographic reconstruction, continental rifting to drifting, carbonatite, REE-Nb mineralization, North China Craton (NCC), Columbia (Nuna) supercontinent