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RONG Kunbo,ZENG Zhigang,YIN Xuebo,CHEN Shuai,WANG Xiaoyuan,QI Haiyan,MA Yao. 2018. Smectite formation in metalliferous sediments near the East Pacific Rise at 13°N. Acta Oceanologica Sinica, 37(9):67-81
Smectite formation in metalliferous sediments near the East Pacific Rise at 13°N
东太平洋海隆13°N附近含金属沉积物中蒙脱石成因
Received:August 14, 2017  
DOI:doi:10.1007/s13131-018-1265-6
Key words:metalliferous sediments  smectite formation  REE  silicon isotope
中文关键词:  含金属沉积物  蒙脱石成因  稀土元素  硅同位素
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.
Author NameAffiliationE-mail
RONG Kunbo Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
University of Chinese Academy of Sciences, Beijing 100049, China 
 
ZENG Zhigang Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
University of Chinese Academy of Sciences, Beijing 100049, China 
zgzeng@ms.qdio.ac.cn 
YIN Xuebo Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China  
CHEN Shuai Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China  
WANG Xiaoyuan Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China  
QI Haiyan Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China  
MA Yao Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, 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 Fe-oxyhydroxides. 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.
中文摘要:
      通过对东太平洋海隆13°N附近E271岩心沉积物中蒙脱石成因的研究可以更好地了解热液物质沉积后的地球化学行为。E271沉积物是典型的含金属沉积物,通过化学淋滤的方法去掉沉积物中的有机质、碳酸盐、生物硅和Fe-Mn氧化物后,对其中的粘土矿物(<2 μm)进行X射线衍射分析,地球化学和硅同位素测定,结果表明粘土矿物来源复杂,伊利石、绿泥石和高岭石可能来自北美洲或中美洲,通过河流或风搬运而来,而蒙脱石极可能是在含金属沉积物中通过热液来源Fe羟基氧化物和二氧化硅以及海水发生反应形成。二氧化硅可能来自硅质微生物化石(硅藻或者放射虫)、热液流体或碎屑矿物,其δ30Si值都高于自生蒙脱石的,表明自生作用过程中Fe羟基氧化物选择性吸附较轻的Si同位素而导致硅同位素分馏。E271粘土矿物中Sm/Fe比值低于含金属沉积物、远端热液羽状流颗粒物和陆源粘土矿物中的,表明蒙脱石自生作用过程中Fe羟基氧化物吸附的稀土元素发生丢失,极有可能是因为稀土元素离子半径过大不能类质同象替换蒙脱石的四面体或八面体位,这降低了含金属沉积物作为稀土元素重要潜在矿产资源的价值。
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