从华北燕辽岩床群到哥伦比亚超大陆巨型裂谷系
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1.中国地质科学院地质力学研究所;2.首都师范大学

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本文为国家自然科学基金项目(41920104004、U2244213、41725011)资助的成果


From the Yanliao sill swarms in the North China Craton to the large–scale continental rift system in the Columbia supercontinent
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1.Institute of Geomechanics, CAGS;2.Capital Normal University

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    摘要:

    近20年的研究工作表明,华北克拉通北部燕辽地区侵入到中元古代沉积地层中的大规模辉绿岩岩床群构成了一个13.2亿年的基性大火成岩省。该大火成岩省与华北克拉通西北缘白云鄂博矿区富稀土–铌火成碳酸岩相伴生。大火成岩省、沉积地层对比和古地磁资料研究结果表明,燕辽大火成岩省与北澳大利亚克拉通代理姆–加里温库大火成岩省是被大陆裂解分割开来的同一个基性大火成岩省的组成部分,显示18~13亿年期间华北克拉通北–北东缘与北澳大利亚克拉通北缘在哥伦比亚(奴那)超大陆中长期相邻(连)。全球14~13亿年大火成岩省及基性岩浆活动的时空分布及其岩石学、地球化学及同位素组成对比研究显示,这些全球广泛分布的大火成岩省或基性岩浆活动主要形成于裂谷环境。结合14亿年左右哥伦比亚超大陆古地理重建结果,发现在哥伦比亚超大陆中存在沿劳伦(北美+格陵兰)克拉通西缘、西伯利亚克拉通西缘及北缘、波罗地克拉通东南缘、西非克拉通西缘及北缘、亚马逊克拉通西南缘、刚果/圣弗朗西斯科克拉通南缘及东缘、卡拉哈里克拉通东缘、华北克拉通北缘及北澳大利亚克拉通北缘分布,长度>15000公里的巨型裂谷系。该巨型裂谷系由一个主裂谷带和三个分支裂谷组成,其中主裂谷带和位于华北与北澳大利亚克拉通之间的分支裂谷发展成了大洋,并导致了大陆分离;而位于西伯利亚东缘、格陵兰北缘和波罗地东缘的13.8亿年分支裂谷,以及位于北美北缘和西伯利亚西南缘的13.5~13.2亿年分支裂谷则为夭折裂谷,未导致大陆裂离。这一巨型裂谷系是哥伦比亚超大陆裂解的重要标志,并可能是其最终裂解的最主要原因。另外,研究结果也显示,虽然全球两个最大规模的火成碳酸岩型稀土矿床,即华北克拉通西北缘的白云鄂博超大型稀土矿床和北美克拉通西缘的Mountain Pass超大型稀土矿床在哥伦比亚超大陆中并不相邻(相连),但却可以通过14~13亿年巨型裂谷系相联系起来,显示这一巨型裂谷系控制了白云鄂博和Mountain Pass大型稀土矿床的形成,并具有较好的稀土及金属成矿潜力。未来需要进一步加强燕辽辉绿岩床群侵位机制与岩浆补给系统,岩床侵位过程中温室气体排放量定量估算及其环境效应,哥伦比亚超大陆中14~13亿年巨型裂谷系的形成机制、深部动力学背景、环境效应及资源能源潜力等方面的研究。

    Abstract:

    Twenty years of research on the Yanliao sill swarms intruded into the Mesoproterozoic strata in the northern North China Craton (NCC) shows that the Yanliao sill swarms constitute a ca. 1.32 Ga mafic large igneous province (LIP) termed as the Yanliao LIP, which is coeval with the REE–Nb rich carbonatites in the Bayan Obo giant REE deposit on the northwestern margin of the NCC. A comparison of intraplate mafic events interpreted as LIPs or portions of LIPs (LIP fragments/remnants due to continental breakup or erosion) from the NCC and North Australian Craton (NAC), in combined with paleomagnetic data indicate that the northern–northeastern margin of the NCC had been connected to the northern margin of the NAC for almost 500 Ma from ca. 1.8 Ga to 1.3 Ga. Spatial and temporal distributions of the 1.4?1.3 Ga LIPs and smaller intraplate mafic magmatic events (interpreted as LIP fragments/remnants) in the refined paleogeographic reconstruction map of Columbia supercontinent, together with previous petrological, geochemical and isotopic results reveal a 1.4–1.3 Ga large-scale continental rift system extending about 15000 km across the Columbia supercontinent. This huge continental rift zone extends along the western Laurentia (North America and Greenland), western–northern Siberia, southeastern Baltica, western–northern West Africa, southwestern Amazonia, southern–eastern Congo/S?o Francisco, eastern Kalahari, northern NCC and northern NAC and consists of a main rift zone and three branch rift zones. The main rift zone along western Laurentia, western–northern Siberia, southeastern Baltica, western–northern West Africa, southwestern Amazonia, southern–eastern Congo/S?o Francisco, eastern Kalahari, northern NCC and northern NAC and the rift zone branch between the NAC and NCC had developed to the drifting stage (new oceans) and resulted in fragmentation and final breakup of Columbia supercontinent. However, the other two rift zone branches including one extending to eastern Siberia, northern Greenland and eastern Baltica (1.38 Ga), and another extending to northern North America and southwestern Siberia (1.35–1.32 Ga) are most likely failed rifts and haven’t resulted in separation of Siberia from Laurentia and Baltica, respectively. The 1.4–1.3 Ga large-scale continental rift system is considered as the main indicator and a proximal reason for final breakup of the Columbia supercontinent. This newly identified huge continental rift zone system had also controlled the distributions of the world's first and second largest REE-Nb deposits (the Bayan Obo deposit on northwestern margin of the NCC and Mountain Pass deposit in western Laurentia) and is most likely a favorable metallogenic belt for other carbonatite-related REE(-Nb) deposits and other metallogenic types such as giant clastic-dominated Zn-Pb-Ag deposits. Future research directions are suggested to focus on the emplacement mechanism and magma plumbing system of the Yanliao LIP, quantitative estimation of greenhouse gases released during emplacement of the Yanliao sill swarms and their environmental effects, the mechanism and deep processes for formation of the 1.4–1.3 Ga huge rift system, and global environmental effects and resource potentials of the 1.4–1.3 Ga large–scale rift system.

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  • 收稿日期:2023-09-16
  • 最后修改日期:2023-11-01
  • 录用日期:2023-11-02
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