| Smectite formation in metalliferous sediments near the East Pacific Rise at 13°N |
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| 引用本文： | 荣坤波,曾志刚,殷学博,陈帅,王晓媛,齐海燕,马瑶.Smectite formation in metalliferous sediments near the East Pacific Rise at 13°N[J].海洋学报(英文版),2018,37(9):67-81. |
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| 作者姓名： | 荣坤波 曾志刚 殷学博 陈帅 王晓媛 齐海燕 马瑶 |
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| 作者单位： | 中国科学院海洋研究所, 海洋地质与环境重点实验室, 青岛, 266071;中国科学院大学, 北京, 100039,中国科学院海洋研究所, 海洋地质与环境重点实验室, 青岛, 266071;青岛海洋科学与技术国家实验室, 海洋矿产资源评价与探测技术功能实验室, 青岛, 266071;中国科学院大学, 北京, 100039,中国科学院海洋研究所, 海洋地质与环境重点实验室, 青岛, 266071,中国科学院海洋研究所, 海洋地质与环境重点实验室, 青岛, 266071,中国科学院海洋研究所, 海洋地质与环境重点实验室, 青岛, 266071,中国科学院海洋研究所, 海洋地质与环境重点实验室, 青岛, 266071,中国科学院海洋研究所, 海洋地质与环境重点实验室, 青岛, 266071 |
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| 基金项目： | The National Natural Science Foundation of China under contract No. 41325021; the National Basic Research Program (973 Program) of China under contract No. 2013CB429700; the National Special Fund for the 12th Five-Year Plan of COMRA under contract No. DY125-12-R-02; the Special Fund for the Taishan Scholar Program of Shandong Province under contract No. ts201511061; the AoShan Talents Program Supported by Qingdao National Laboratory for Marine Science and Technology under contract No. 2015ASTP-0S17. |
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| 摘 要： | A 43 cm long E271 sediment core collected near the East Pacific Rise(EPR) at 13°N were studied to investigate the origin of smectite for understanding better the geochemical behavior of hydrothermal material after deposition.E271 sediments are typical metalliferous sediments. After removal of organic matter, carbonate, biogenic opal,and Fe-Mn oxide by a series of chemical procedures, clay minerals(2 μm) were investigated by X-ray diffraction,chemical analysis and Si isotope analysis. Due to the influence of seafloor hydrothermal activity and close to continent, the sources of clay minerals are complex. Illite, chlorite and kaolinite are suggested to be transported from either North or Central America by rivers or winds, but smectite is authigenic. It is enriched in iron, and its contents are highest in clay minerals. Data show that smectite is most likely formed by the reaction of hydrothermal Fe-oxyhydroxide with silica and seawater in metalliferous sediments. The Si that participates in this reaction may be derived from siliceous microfossils(diatoms or radiolarians), hydrothermal fluids, or detrital mineral phases. And their δ30 Si values are higher than those of authigenic smectites, which implies that a Si isotope fractionation occurs during the formation because of the selective absorption of light Si isotopes onto Feoxyhydroxides. Sm/Fe mass ratios(a proxy for overall REE/Fe ratio) in E271 clay minerals are lower than those in metalliferous sediments, as well as distal hydrothermal plume particles and terrigenous clay minerals. This result suggests that some REE are lost during the smectite formation, perhaps because their large ionic radii of REE scavenged by Fe-oxyhydroxides preclude substitution in either tetrahedral or octahedral lattice sites of this mineral structure, which decreases the value of metalliferous sediments as a potential resource for REE.
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| 关 键 词： | 含金属沉积物 蒙脱石成因 稀土元素 硅同位素 |
| 收稿时间： | 2017/8/14 0:00:00 |
Smectite formation in metalliferous sediments near the East Pacific Rise at 13°N |
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| RONG Kunbo,ZENG Zhigang,YIN Xuebo,CHEN Shuai,WANG Xiaoyuan,QI Haiyan and MA Yao.Smectite formation in metalliferous sediments near the East Pacific Rise at 13°N[J].Acta Oceanologica Sinica,2018,37(9):67-81. |
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| Authors: | RONG Kunbo ZENG Zhigang YIN Xuebo CHEN Shuai WANG Xiaoyuan QI Haiyan and MA Yao |
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| Affiliation: | 1.Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology,Chinese Academy of Sciences,Qingdao,China;2.Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology,Qingdao,China;3.University of Chinese Academy of Sciences,Beijing,China |
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| Abstract: | A 43 cm long E271 sediment core collected near the East Pacific Rise (EPR) at 13°N were studied to investigate the origin of smectite for understanding better the geochemical behavior of hydrothermal material after deposition. E271 sediments are typical metalliferous sediments. After removal of organic matter, carbonate, biogenic opal, and Fe-Mn oxide by a series of chemical procedures, clay minerals (<2 μm) were investigated by X-ray diffraction, chemical analysis and Si isotope analysis. Due to the influence of seafloor hydrothermal activity and close to continent, the sources of clay minerals are complex. Illite, chlorite and kaolinite are suggested to be transported from either North or Central America by rivers or winds, but smectite is authigenic. It is enriched in iron, and its contents are highest in clay minerals. Data show that smectite is most likely formed by the reaction of hydrothermal Fe-oxyhydroxide with silica and seawater in metalliferous sediments. The Si that participates in this reaction may be derived from siliceous microfossils (diatoms or radiolarians), hydrothermal fluids, or detrital mineral phases. And their δ30Si values are higher than those of authigenic smectites, which implies that a Si isotope fractionation occurs during the formation because of the selective absorption of light Si isotopes onto Feoxyhydroxides. Sm/Fe mass ratios (a proxy for overall REE/Fe ratio) in E271 clay minerals are lower than those in metalliferous sediments, as well as distal hydrothermal plume particles and terrigenous clay minerals. This result suggests that some REE are lost during the smectite formation, perhaps because their large ionic radii of REE scavenged by Fe-oxyhydroxides preclude substitution in either tetrahedral or octahedral lattice sites of this mineral structure, which decreases the value of metalliferous sediments as a potential resource for REE. |
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| Keywords: | metalliferous sediments smectite formation REE silicon isotope |
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