| 浅谈前寒武纪条带状铁建造的沉积-变质成矿过程 |
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| 引用本文： | 李旭平,陈妍蓉.浅谈前寒武纪条带状铁建造的沉积-变质成矿过程[J].岩石学报,2021,37(1):253-268. |
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| 作者姓名： | 李旭平 陈妍蓉 |
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| 作者单位： | 山东省沉积成矿作用实验室, 山东科技大学地球科学与工程学院, 青岛 266510 |
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| 基金项目： | 本文受国家自然科学基金项目（U1906207、4171101197）和山东科技大学科研创新团队（2015TDJH101）联合资助. |
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| 摘 要： | 条带状铁建造(BIF)是3.5~1.8Ga前陆架和洋盆的常见沉积物。前寒武纪条带状铁建造构成了世界上重要的铁矿资源。虽然它们成矿过程及其演化的许多方面的问题仍未解决,但人们普遍认为,它们沉积方式的长期变化与地球的环境和地球化学演化有关。条带状铁建造记录了前寒武纪古海洋、古环境、大气条件和细菌代谢条件以及铁的来源和沉积过程。大型BIF沉积与大火成岩省有成因联系,其铁的来源与火山物质加入的海底热液体系有关,或有陆缘岩石风化的无机物产物加入,越靠近陆缘,陆源碎屑物质加入的越多。然而,在太古宙到古元古代期间,BIF沉积的深水盆地中陆源物质的加入很少。那时的铁建造沉积在缺氧的海洋中,通过微生物的光合作用、无氧光合氧化和紫外光线辐射氧化等机制对溶解的二价铁进行氧化,从而形成三价铁氢氧化物和氧化物的沉积。大多数BIF大型矿床,自其在沉积环境中形成以来,它们在从太古宙直至中生代的漫长的地质历史演化过程中经历了铁矿的品位由低到高转化的复杂地质过程,一般经历了深部交代变质作用的除硅、除碳酸岩矿物的富集成矿和浅部风化富集成矿过程。许多BIF铁矿经历了从绿片岩相到角闪岩相变质作用,但到达的压力条件都不是很高,这或许与俯冲的高密度BIF铁矿难以折返的动力学机制有关。迄今为止,变质作用、尤其是高级变质作用对成矿过程的影响研究较少,是今后值得关注的领域。
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| 关 键 词： | BIF铁矿 太古宙到早元古代 沉积过程 变质作用 成矿作用 |
| 收稿时间： | 2020/10/1 0:00:00 |
| 修稿时间： | 2020/12/5 0:00:00 |
A brief discussion on the depositional and metamorphic mineralization of Precambrian banded iron formations |
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| LI XuPing,CHEN YanRong.A brief discussion on the depositional and metamorphic mineralization of Precambrian banded iron formations[J].Acta Petrologica Sinica,2021,37(1):253-268. |
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| Authors: | LI XuPing CHEN YanRong |
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| Institution: | Key Laboratory of Sedimentary Mineralization & Sedimentary Minerals in Shandong Provinces, College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266510, China |
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| Abstract: | Banded iron formations (BIFs) are sediments commonly deposited in continental shelf and ocean basin 3.5~1.8Ga ago. Precambrian BIF constitutes an important iron ore resource in the world. Although many aspects of their metallogenic processes and evolution remain unresolved, it is widely accepted that the long-term changes of their deposition are related to the environmental and geochemical evolution of Earth. BIF records the Precambrian paleooceanic, paleoenvironment, atmospheric and bacterial metabolism conditions as well as its iron source and deposition process. Large BIF deposits are genetically related to large igneous provinces, and the source of iron is related to the seafloor hydrothermal system mixed with volcanic material, or the inorganic products of the weathering of terrestrial rocks. The closer to the continental margin, the more terrigenous debris is added. However, in the deep ocean basins of BIF deposition during the Archaean to Early Paleoproterozoic, there was little addition of terrestrial sources. At that time, the iron formation was deposited in the oxygen-deficient ocean, and the dissolved Fe2+ was oxidized through the mechanisms of microbial photosynthesis, anaerobic photosynthetic and ultraviolet radiation oxidation, so as to facilitate the deposition of trivalent iron hydroxide and oxide. Most large BIFs, formed in sedimentary basins, experienced a long-term complex geological process for the transformation of low grade to high grade of iron ore from Archean to Mesozoic, and generally experienced hypogene metasomatic metamorphism to remove the silicon and carbonate minerals and thus enrich in iron oxides, and afterwards supergene-modified and iron enrichment process. Many BIF iron ores undergo metamorphism from greenschist facies to amphibolite facies, but the pressure conditions are not very high, which may be related to the dynamic mechanism of difficult exhumation of high-density BIF iron ores from subduction processes. Up to now, the influence of metamorphism, especially high grade metamorphism, on the mineralization process has been rarely studied, so it is an area worthy of attention in the future. |
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| Keywords: | BIF iron ore Archaea to Early Proterozoic Sedimentation process Metamorphism Mineralization |
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