TERRAPUB Geochemical Journal
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Geochemical Journal, Vol. 43 (No. 5), pp. e17-e22, 2009

EXPRESS LETTER

H2 generation by experimental hydrothermal alteration of komatiitic glass at 300°C and 500 bars: A preliminary result from on-going experiment

Motoko Yoshizaki,1,2 Takazo Shibuya,2 Katsuhiko Suzuki,2,3 Kenji Shimizu,2,3 Kentaro Nakamura,2 Ken Takai,2,4 Soichi Omori1 and Shigenori Maruyama1

1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
2Precambrian Ecosystem Laboratory, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan
3Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan
4Subsurface Geobiology Advanced Research (SUGAR) project, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan

(Received April 7, 2009; Accepted August 28, 2009; Online published September 10, 2009)

Abstract: Hydration of komatiite can be a source of significant amount of hydrogen in the Hadean and early Archean ocean floor. We report the first direct evidence for this process based on the results of our hydrothermal alteration experiments on the synthetic komatiitic glass at 300°C and 500 bars. Komatiitic glass was synthesized by dehydration and remelting of serpentinized Al-depleted komatiite collected from the early Archean Komati Formation, the Barberton Greenstone Belt, South Africa. Though the run is still continuing in our lab, the observed accumulation of hydrogen (2.4 mmol/kg) over 2,600 hours is truly significant and is comparable to those observed by hydration of peridotitic rocks. Our results suggest that hydrothermal alteration of komatiites may have provided the source of H2 in the vicinity of hydrothermal vents that fueled the early evolution of living ecosystems in the Hadean and early Archean.
Key words: hydrothermal alteration, komatiitic glass, laboratory experiment, early Earth, ultramafic rock


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