初期地球の海底熱水系に関する地質学的,地球化学的研究

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  • 渋谷 岳造
    独立行政法人海洋研究開発機構プレカンブリアンエコシステムラボユニット

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  • Geological and geochemical studies on seafloor hydrothermal system in the early Earth
  • 2012年度日本地球化学会奨励賞受賞記念論文 初期地球の海底熱水系に関する地質学的,地球化学的研究
  • 2012ネンド ニホン チキュウ カガッカイ ショウレイショウ ジュショウ キネン ロンブン ショキ チキュウ ノ カイテイ ネッスイケイ ニ カンスル チシツガクテキ,チキュウ カガクテキ ケンキュウ

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抄録

Mid-ocean ridges are places where interactions between seawater and oceanic crust take place. Hydrothermal interactions govern the chemistry of the oceans while hydrothermal vent fields host unique and diverse biological communities even in barren ocean floor settings, and are candidates for the birthplace of the earliest life forms. This paper presents the important roles of the hydrothermal carbonatization of Archean oceanic crust that is one of the characteristic seafloor alterations in the early Earth. Based on the mineralogical, geochemical, and geological features of calcite in the Archean greenstones, the CO2 flux from ocean to oceanic crust was estimated to be two orders of magnitude larger than the modern value, which points to the significance of seafloor hydrothermal carbonatization in the Archean carbon cycle. Furthermore, thermodynamic calculations of phase equilibria in the high-temperature alteration zone indicate that the hydrothermal fluid was alkaline due to the presence of calcite in the alteration minerals under a high-CO2 condition, and predict a generation of SiO2-rich and Fe-poor hydrothermal fluids in the subseafloor hydrothermal system. 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.

収録刊行物

  • 地球化学

    地球化学 47 (4), 193-207, 2013

    一般社団法人日本地球化学会

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