Low silica activity for hydrogen generation during serpentinization: An example of natural serpentinites in the Mineoka ophiolite complex, central Japan
Low silica activity for hydrogen generation during serpentinization: An example of natural serpentinites in the Mineoka ophiolite complex, central Japan
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DOI：
10.1016/j.epsl.2010.07.045
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发表时间：
2010-09
影响因子：
5.3
通讯作者：
I. Katayama;I. Kurosaki;K. Hirauchi
中科院分区：
文献类型：
--
作者：
I. Katayama;I. Kurosaki;K. Hirauchi
对峰冈蛇绿岩杂岩中蛇纹岩的结构演化进行了研究，以限制蛇纹岩热液喷口系统中产氢的自然环境。从峰冈蛇绿岩的蛇纹岩的结构关系表明至少有两个阶段的蛇纹石化过程中，与橄榄石的蛇纹石和水镁石的网状结构的替代，其次是磁铁矿轴承或无蛇纹石静脉的发展。蛇纹石化过程中产生的氢，伴随着磁铁矿的形成，涉及到二氧化硅贫化反应，证明了低丰度的蛇纹石在磁铁矿的静脉和磁铁矿的假像的斜方辉石的情况下。残留橄榄石晶体中含有甲烷和氢的包裹体提供了产生氢和强还原条件的直接证据;甲烷和氢的产生可能为沿着海底的热液喷口系统中的微生物活动提供了合适的环境。我们的研究结果表明，低硅活性在蛇纹石化过程中的氢的生成中起着关键作用，低硅活性环境是可能的，在富含橄榄石的岩石，如纯橄榄岩，或在局部不平衡期间，在其他硅贫岩石在地幔岩石圈。
The textural evolution in the serpentinite of the Mineoka ophiolite complex has been investigated to constrain the natural environment for hydrogen production in the serpentinite-hosted hydrothermal vent systems. Textural relations of the serpentinites from the Mineoka ophiolite indicate at least two stages in the process of serpentinization, with the replacement of olivine by a mesh texture of serpentine and brucite, followed by the development of magnetite-bearing or -free serpentine veins. The generation of hydrogen during serpentinization, which accompanies the formation of magnetite, involves a silica-depletion reaction, as evidenced by the low abundance of serpentine in the magnetite-bearing veins and the absence of magnetite in pseudomorphs of orthopyroxene. Direct evidence for the production of hydrogen and strongly reducing conditions is provided by CH4and H2-bearing inclusions in relic olivine crystals; the production of methane and hydrogen may have provided a suitable environment for microbial activity in hydrothermal vent systems along the seafloor. Our results indicate that low silica activity plays a key role in the generation of hydrogen during serpentinization, and that low silica activity environments are possible in olivine-rich rocks such as dunite, or during local disequilibrium in other silica-poor rocks in the mantle lithosphere.