Thesis Advisor曾志刚
Degree Grantor中国科学院大学
Place of Conferral中国科学院海洋研究所
Degree Discipline海洋地质

对东太平洋海隆13°N洋中脊西侧含金属沉积物(站号:E271)进行矿物学和地球化学分析,并与前人在洋中脊轴部地区的热液沉积物研究结果对比,分析相同热液区远端含金属沉积物和近喷口含金属沉积物的不同成因,及其对元素赋存状态造成的差异,通过对粘土粒级组分(< 2μm)的研究,探究自生蒙皂石的成因,探讨自生作用过程中Si的物质来源,以及Si同位素和稀土元素的地球化学行为。



Other Abstract

Mineralogy and element geochemistry of a 43 cm long E271 sediment core collected from the East Pacific Rise (EPR) near 13°N were studied to better understand the differences in the orgin and element occurrence states between near-vent and distal metalliferous sediments in the same hydrothermal fields by comparison with the hydrothermal sediments from the EPR axis. The clay minerals (< 2μm) in the metalliferous sediments were analyzed to investigate the smectite formation, and to discuss the origin of Si and the geochemical behavior of the Si isotope and REE during the authigenic process.

Sediment samples collected from E271 site, along the ridge flank on west sides of the EPR are distal metalliferous sediments that result from hydrothermal non-buoyant plume fallout. However, samples (Site 17A-EPR-TVG1) from the slope of a hydrothermal mound on the EPR axis are near-vent metalliferous sediments that are formed by mass-wasting and erosion of sulfide edifices, and hydrothermal plume fallout of sulfides. Near-vent metalliferous sediments are richer in Fe, Cu, and Zn than distal metalliferous sediments. In terms of sequential leaching, although most of element occurrence states are basically similar in the two kinds of metalliferous sediments, Fe, Cu, Zn, Mo, Y, and REE are mainly present in the residual fraction of near-vent sediments, they mainly occur in the Fe-Mn oxide fraction of distal sediments. The shale-normalized REE distribution pattern of the sediments shows a peculiar positive Eu anomaly similar to those of hydrothermal fluids, suggesting a hydrothermal origin, but those of distal sediments show Ce depletion, characteristic of seawater.

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. Data show that smectite is most likely formed by the reaction of hydrothermal Fe-oxyhydroxide with silica and seawater in metalliferous sediments. The SiO2 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 the Fe-Mn oxide fraction of the E271 sediments. 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.

Subject Area海洋地质学
MOST Discipline Catalogue理学::海洋科学
Document Type学位论文
Recommended Citation
GB/T 7714
荣坤波. 东太平洋海隆13°N地区含金属沉积物中蒙皂石成因[D]. 中国科学院海洋研究所. 中国科学院大学,2018.
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