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- Title
Reactions between komatiite and CO-rich seawater at 250 and 350 °C, 500 bars: implications for hydrogen generation in the Hadean seafloor hydrothermal system.
- Authors
Ueda, Hisahiro; Shibuya, Takazo; Sawaki, Yusuke; Saitoh, Masafumi; Takai, Ken; Maruyama, Shigenori
- Abstract
To understand the chemical nature of hydrothermal fluids in the komatiite-hosted seafloor hydrothermal system in the Hadean, we conducted two hydrothermal serpentinization experiments involving synthetic komatiite and a CO-rich acidic NaCl fluid at 250 and 350 °C, 500 bars. During the experiments, the komatiites were strongly carbonated to yield iron-rich dolomite (3-9 wt.% FeO) at 250 °C and calcite (<0.8 wt.% FeO) at 350 °C, respectively. The carbonation of komatiites suppressed H generation in the fluids. The steady-state H concentrations in the fluid were approximately 0.024 and 2.9 mmol/kg at 250 and 350 °C, respectively. This correlation between the Fe content in carbonate mineral and the H concentration in the fluid suggests that the incorporation of ferrous iron into the carbonate mineral probably limited magnetite formation and consequent generation of hydrogen during the serpentinization of komatiites. The H concentration of the fluid at 350 °C corresponds to that of modern H-rich seafloor hydrothermal systems, such as the Kairei hydrothermal field, where hydrogenotrophic methanogens dominate in the prosperous microbial ecosystem. Accordingly, the high-temperature serpentinization of komatiite would provide the H-rich hydrothermal environments that were necessary for the emergence and early evolution of life in the Hadean ocean. In contrast, H-rich fluids may not have been generated by serpentinization at temperatures below 250 °C because carbonate minerals become more stable with decreasing temperature in the komatiite-HO-CO system.
- Subjects
KOMATIITE; CHEMICAL reactions; STEADY state conduction; MAGNETITE; HADEAN
- Publication
Progress in Earth & Planetary Science, 2016, Vol 3, Issue 1, p1
- ISSN
2197-4284
- Publication type
Article
- DOI
10.1186/s40645-016-0111-8