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論文 |
論文
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Mizukami, Tomoyuki ; Yokoyama, Hironori ; Hiramatsu, Yoshihiro ; Arai, Shoji ; Kawahara, Hirokazu ; Nagaya, Takayoshi ; Wallis, Simon R.
概要:
It is known that plate boundaries in subduction zones show heterogeneous slip nature with strongly coupled seismogenic z
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ones and various types of episodic tremor and slip (ETS) zones. In order to examine the petrological controls on the large-scale structure, we compared recent geophysical observations in the Shikoku area, southwest Japan with petrological models of the hanging wall mantle wedge. As a result, we found a close relationship between mineral assemblages in the mantle wedge and the characteristics of slow slip behaviour recorded in the Shikoku area: Short-term ETSs take place in the antigorite + olivine stability field and silent long-term slow slip events (SSEs) take place in the antigorite+brucite stability field. Based on observations of natural antigorite serpentinites, we propose a model that the dominant serpentinization reaction in the mantle wedge changes with increasing depth resulting in variable extents of pore fluid pressures along slip planes. The serpentinization reaction in the antigorite+brucite stability field (olivine + H2O → antigorite + brucite) proceeds at the expense of water. This is consistent with moderately elevated pore pressures inferred for long-term SSEs. The existence of weak brucite enhances the development of shear zones oblique to the main foliation. The resultant anastomosing network provides fluid pathways that may help reduce pore pressures on slip planes. In contrast, progress of the serpentinization reaction in the antigorite + olivine stability field (olivine + H2O + SiO2 → antigorite) results in a large amount of residual water that contributes to further increase pore fluid pressures on slip planes of short-term SSEs. Our results imply that understanding of serpentinization reactions and their contributions to fluid networks in mantle wedge is important in constructing quantitative 3-D models for strain evolutions along plate boundaries. © 2014 Elsevier B.V.
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論文 |
論文
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矢部, 太章 ; 福士, 圭介 ; 伊藤, 弘志 ; 窪田, 宗弘 ; 桝谷, 優輔
概要:
金沢大学環日本海域環境研究センター<br />Magnesium oxide with high specific surface area (HS-MgO) has been widely used for the sorbent mat
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erial for hazardous anions from contaminated solutions. Because the magnesium oxide is unstable under ambient conditions, alteration behavior of HS-MgO was investigated by batch alteration experiments as a function of time in electrolyte solutions under ambient and nitrogen atmospheres. The mineralogy of reacted solid was characterized by means of X-ray diffraction, scanning electron microscope and measurements of specific surface area. The solution chemistry of reacted solutions was examined by pH meter and high pressure liquid chromatography for measurement of dissolved Mg concentration. Periclase in HS-MgO almost completely transforms to brucite within 8 hours. The specific surface area decreases from 110m^2/g of unaltered HS-MgO to 60m^2/g by the alteration. The alteration process is characterized by dissolution of periclase and precipitation of brucite from solution. The rate limiting step of the transformation process is the dissolution of periclase. This study indicates that the alteration process must influence on the uptake of hazardous anion by HS-MgO.
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