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题名: 东太平洋海隆13°N附近热液硫化物形成过程
作者: 陈代庚
学位类别: 博士
答辩日期: 2009-07-18
授予单位: 中国科学院海洋研究所
授予地点: 海洋研究所
关键词: 东太平洋海隆13°N附近 ; 硫化物 ; 形成过程 ; 布拜图
其他题名: The formation of the hydrothermal sulfide near 13ºN on the East Pacific Rise
中文摘要: 东太平洋海隆13°N附近热液区构造环境上属于快速扩张中心,该区段洋中脊拉张速率达到了12cm/yr,轴部地堑平均水深2630m。本文即是对该研究区(103°54.41´W, 12°42.68´N)获得的热液烟囱体硫化物样品展开了研究。借助偏光显微镜观察了硫化物显微结构特征,并分析了硫化物中的矿物组合。东太平洋海隆13°N附近热液硫化物中常见矿物为Fe硫化物和Zn硫化物,并经历了由早期Fe硫化物为主转变为晚期成熟化以Zn硫化物为主的过程;根据观察到的显微结构,东太平洋海隆13ºN附近热液硫化物的形成至少可划分出四个阶段即黄铁矿阶段、黄铜矿阶段、黄铁矿-闪锌矿和闪锌矿阶段。 建立了热液硫化物样品中常、微量元素的测试方法,测定了东太平洋海隆13°N附近常、微量元素组成,并与有沉积物覆盖的北胡安德富卡脊Middle Valley烟囱体硫化物和弧后环境的北斐济盆地富Zn型烟囱体硫化物进行了对比。以Cu、Pb、Zn相对含量百分比划分,东太平洋海隆13ºN附近热液硫化物属富Zn型。 阐述了东太平洋海隆13ºN附近热液硫化物微量元素组成空间变化特征及元素比值在样品中的演化,并分析了常微量元素之间及元素/Cu值与1/Cu之间的相关性。Cd、Ga、In主要以类质同像的形式存在于Zn硫化物中,Co的主要寄主矿物是Zn硫化物。在东太平洋海隆13°N附近热液硫化物的形成过程中,常量元素Cu、微量元素Mo趋向于在高温(T>300℃)条件下自流体相沉淀。对东太平洋海隆13°N附近热液硫化物而言,硫化物样品中Cu含量、Cu/Pb及Mo/Pb值可以为形成硫化物的流体的温度变化提供指示性佐证;对应于形成硫化物的流体温度由高温至低温的演化,流体化学组成也相应地发生了演化,其中Sr、Ba、Au等微量元素按指数函数规律富集。对获取的硫化物样品进行了R型因子分析,旋转后获得的因子可以区分出形成硫化物的流体的温度和化学组成这两个因素的影响。 在热力学计算的基础上绘制了东太平洋海隆13°N附近热液Fe-S-H2O系统布拜图,据此阐明了实际情况下东太平洋海隆13°N附近热液流体由高温至低温的过程中,硫化物中优势矿物黄铁矿的稳定场的演化。在此基础上结合已有的动力学实验和硫同位素分馏的研究成果,揭示了沉淀硫化物的热液活动过程中形成优势矿物黄铁矿的可能的主要化学反应历程和形成硫化物的流体的温度变化对黄铁矿形成的热力学机制的影响。
英文摘要: The hydrothermal field near 13ºN on the East Pacific Rise is located at a segment where the opening rate at this is 12cm/yr, i.e., a tectonic environment of fast-spreading center. The average water depth of the axial graben floor is 2630m. Detailed studies were conducted on the hydrothermal sulfide sampled from this area (103°54.41´W, 12°42.68´N). Microstructure features of the hydrothermal sulfide were observed in the polarizing microscope and mineral assemblages were also exhibited. The hydrothermal sulfide near 13ºN on the East Pacific Rise is mainly composed of Fe-sulfide and Zn-sulfide minerals, and has experienced the transformation from Fe-sulfides predominance at an early stage to Zn-sulfides predominance at a late stage. According to observed microstructures, the formation of the hydrothermal sulfide near 13ºN on the East Pacific Rise can be divided into four stages, namely, pyrite stage, chalcopyrite stage, pyrite-sphalerite stage and sphalerite stage. Test procedures of major and trace elements in hydrothermal sulfide samples were established, and major and trace element compositions of the hydrothermal sulfide near 13ºN on the East Pacific Rise were determined on this basis. Characteristics of compositions of the hydrothermal sulfide near 13ºN on the East Pacific Rise were contrasted with chimney sulfides from Middle Valley sediment-hosted hydrothermal system, northern Juan de Fuca Rdge and North Fiji back-arc basin. According to relative percentages of Cu, Pb, Zn (sum of Cu, Pb, Zn contents is assumed as 100%), the hydrothermal sulfide near 13ºN on the East Pacific Rise can be classified as Zn-rich type. Space variations of trace element compositions and evolution of elemental ratios in samples were illustrated. Correlations between major elements and trace elements, and between element ratios (the denominator is Cu) and 1/Cu ratios of the hydrothermal sulfide near 13ºN on the East Pacific Rise were both discussed. Trace elements such as Cd, Ga and In mainly exist in Zn-sulfides in the form of isomorphism. Moreover, Zn-sulfides are the main host minerals of Co. During the formation of the hydrothermal sulfide near 13ºN on the East Pacific Rise, Cu and Mo both tended to precipitated from fluid phases at high temperatures(>300℃). Cu contents, ratios of Cu/Pb and Mo/Pb of sulfide samples can play a significant role as diagnostic indicator of the temperature variations of hydrothermal fluids which formed the sulfide. During the evolution (from high temperatures to low temperatures) of hydrothermal fluids which formed the sulfide, compositions of the hydrothermal fluids evolved at the same time, especially trace metals such as Sr, Ba and Au were enriched exponentially. Factor analyses were also performed on obtained samples, and obtained factors through rotation may distinguish the influences of temperatures and geochemical composition of hydrothermal fluids which formed the sulfide. Pourbaix diagrams of Fe-S-H2O hydrothermal system near 13ºN on the East Pacific Rise were drawn by use of thermodynamic calculations, which illustrated the changes of predominance field of precipitation of the pyrite from hydrothermal systems in practical situations during the evolution (from high temperatures to low temperatures) of hydrothermal fluids which formed the sulfide. On the basis of combination with existing research on dynamic experiments and sulfur isotope fractionation, potential chemical reaction pathways which formed the predominant mineral (i.e., pyrite) during marine hydrothermal activities which precipitated sulfides were brought out, and the influences of temperatures of hydrothermal fluids which formed the sulfide on thermodynamic mechanism of the formation of pyrite were probed into.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.qdio.ac.cn/handle/337002/1174
Appears in Collections:海洋环流与波动重点实验室_学位论文

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东太平洋海隆13°N附近热液硫化物形成过程.陈代庚[d].中国科学院海洋研究所,2009.20-25
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