TY - JOUR
T1 - Highly alkaline, high-temperature hydrothermal fluids in the early Archean ocean
AU - Shibuya, Takazo
AU - Komiya, Tsuyoshi
AU - Nakamura, Kentaro
AU - Takai, Ken
AU - Maruyama, Shigenori
N1 - Funding Information:
We thank M. Terabayashi for providing information on the North Pole greenstones. We are also grateful to P. A. Cawood for editorial handling, and anonymous reviewers for their valuable comments and suggestions. This research was partially supported by the 21st Century COE Program “How to build habitable planets,” Tokyo Institute of Technology, sponsored by the Ministry of Education, Culture, Sports, Technology and Science, Japan. T.S. is grateful for a Research Fellowship of the Japan Society for the Promotion of Science for Young Scientists.
PY - 2010/10/1
Y1 - 2010/10/1
N2 - Based on the petrology of hydrothermally altered Archean basaltic greenstones, thermodynamic calculations of phase equilibria were conducted to estimate the composition of a high-temperature (~350°C) hydrothermal fluid in an Archean subseafloor basalt-hosted hydrothermal system. The results indicate that the hydrothermal fluid was highly alkaline attributed to the presence of calcite in the alteration minerals under a high-CO2 condition, and predict a generation of SiO2-rich, Fe-poor hydrothermal fluids in the Archean subseafloor hydrothermal system. The chemically reactive mixing zones between alkaline hydrothermal fluids and slightly acidic-neutral seawater are characterized by inverse pH and chemical polarity to modern hydrothermal systems, leading to extensive precipitation of silica and iron oxyhydroxides on/under the seafloor. Such processes can be responsible for the abiotic formation of voluminous chert and subseafloor silica dike, the mechanism of silicification, and the pH-controlled generation of banded iron formation that has been arising mainly from the redox chemistry in the Archean ocean. Such high-temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life.
AB - Based on the petrology of hydrothermally altered Archean basaltic greenstones, thermodynamic calculations of phase equilibria were conducted to estimate the composition of a high-temperature (~350°C) hydrothermal fluid in an Archean subseafloor basalt-hosted hydrothermal system. The results indicate that the hydrothermal fluid was highly alkaline attributed to the presence of calcite in the alteration minerals under a high-CO2 condition, and predict a generation of SiO2-rich, Fe-poor hydrothermal fluids in the Archean subseafloor hydrothermal system. The chemically reactive mixing zones between alkaline hydrothermal fluids and slightly acidic-neutral seawater are characterized by inverse pH and chemical polarity to modern hydrothermal systems, leading to extensive precipitation of silica and iron oxyhydroxides on/under the seafloor. Such processes can be responsible for the abiotic formation of voluminous chert and subseafloor silica dike, the mechanism of silicification, and the pH-controlled generation of banded iron formation that has been arising mainly from the redox chemistry in the Archean ocean. Such high-temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life.
KW - Alkaline hydrothermal fluid
KW - Archean chert
KW - Banded iron formation
KW - Basaltic greenstone
KW - Carbonatization
KW - Silicification
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U2 - 10.1016/j.precamres.2010.08.011
DO - 10.1016/j.precamres.2010.08.011
M3 - Article
AN - SCOPUS:77957270500
SN - 0301-9268
VL - 182
SP - 230
EP - 238
JO - Precambrian Research
JF - Precambrian Research
IS - 3
ER -