17:15 〜 18:45
[MIS19-P04] Experimental study on H2 generation through serpentinization of Fe-rich olivine
キーワード：蛇紋岩化作用、かんらん石、水-岩石反応、実験
Serpentinization of ultramafic rock including olivine has been proposed to occur in Earth and other planetary bodies such as Mars (e.g., Ehlmann et al., 2010). The serpentinization of olivine produces secondary minerals such as serpentine, brucite, and magnetite. Along with these secondary minerals, molecular hydrogen is produced by the redox reaction associated with ferrous Fe through serpentinization. H2-rich hydrothermal fluids would have driven prebiotic chemical evolution and the development of biotic energy metabolisms (e.g., Amend and McCollom 2009; Shibuya et al., 2016). In addition, the hydrogen molecule has been known as one of the atmospheric components of early Earth and Mars. Therefore, quantifying the amount of H2 generation is an important subject. Some thermodynamic calculations have shown that the olivine composition (Mg/Fe ratio) is an important factor in the amount of H2 production (Klein et al., 2013; McCollom. et al., 2022). However, most experiment studies for these reactions have been conducted by using Mg-rich olivine (Fo~90) which is commonly exposed in the Earth (e.g., Allen and Seyfreid, 2003) and the examinations for other compositions of olivine are still poorly reported. Therefore, the experimental evaluation of the potential for H2 generation of olivine with various compositions through the serpentinization is necessary.
In this study, we conducted hydrothermal serpentinization experiments that simulate the reactions between various composition olivine (Fa–Fo80) and NaCl solution at 500 bars, using a batch-type (closed system) hydrothermal reactor at JAMSTEC.
One of the results which simulate the reactions of olivine (#Mg=70–80) at 300 °C reveals that the alkaline and H2-rich fluids (over 100 mmol/kg) are produced, which is consistent with the preceding thermodynamic calculations (McCollom. et al., 2022). The H2 concentrations are much higher than those in other experimental studies using olivine (#Mg≈90)(e.g., Shibuya et al., 2015). Under 300 °C, Fe-rich olivine which are commonly observed on the surface of Mars could have the great potentials to produce H2, compared to terrestrial Mg-rich olivine. In this study, to predict the amount of H2 generation of olivine with various compositions, we show the relationships between the H2 concentration of fluids and the run products.
In this study, we conducted hydrothermal serpentinization experiments that simulate the reactions between various composition olivine (Fa–Fo80) and NaCl solution at 500 bars, using a batch-type (closed system) hydrothermal reactor at JAMSTEC.
One of the results which simulate the reactions of olivine (#Mg=70–80) at 300 °C reveals that the alkaline and H2-rich fluids (over 100 mmol/kg) are produced, which is consistent with the preceding thermodynamic calculations (McCollom. et al., 2022). The H2 concentrations are much higher than those in other experimental studies using olivine (#Mg≈90)(e.g., Shibuya et al., 2015). Under 300 °C, Fe-rich olivine which are commonly observed on the surface of Mars could have the great potentials to produce H2, compared to terrestrial Mg-rich olivine. In this study, to predict the amount of H2 generation of olivine with various compositions, we show the relationships between the H2 concentration of fluids and the run products.