Highly alkaline, high-temperature hydrothermal fluids in the early Archean ocean

Takazo Shibuya, Tsuyoshi Komiya, Kentaro Nakamura, Ken Takai, Shigenori Maruyama

    Research output: Contribution to journalArticlepeer-review

    65 Citations (Scopus)

    Abstract

    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.

    Original languageEnglish
    Pages (from-to)230-238
    Number of pages9
    JournalPrecambrian Research
    Volume182
    Issue number3
    DOIs
    Publication statusPublished - Oct 1 2010

    Keywords

    • Alkaline hydrothermal fluid
    • Archean chert
    • Banded iron formation
    • Basaltic greenstone
    • Carbonatization
    • Silicification

    ASJC Scopus subject areas

    • Geology
    • Geochemistry and Petrology

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