Geochemical study of crustal evolution in the early stage of the Earth

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  • SHIMIZU Hiroshi
    Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University

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Other Title
  • 地殻の初期進化に関する地球化学的研究
  • 1999年度日本地球化学会賞受賞記念論文 地殻の初期進化に関する地球化学的研究
  • 1999ネンド ニホン チキュウ カガクカイショウ ジュショウ キネン ロンブン チカク ノ ショキ シンカ ニ カンスル チキュウ カガクテキ ケンキュウ

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This paper reviews geochemical study of crustal evolution in the early stage of the Earth on the basis of La-Ce and Sm-Nd isotopic and REE geochemistry on the Archean gneisses and iron-formations from West Greenland and Archean cherts from Western Australia. The results are summarized as follows. (1) The REE patterns of original materials for the Amitsoq gneisses, West Greenland, had been fractionated in the very early stage of the Archean. (2) The sources for the Archean iron-formations from West Greenland had a chiefly chondritic or rather mantle-like depleted nature without a notable long-term negative Ce anomaly. (3) Large contribution of hydrothermal solution derived from depleted or chondritic mantle is suggested to the Archean Marble Bar Cherts, Western Australia, in contrast to Phanerozoic biogenic cherts. These results imply REE fractionation (i.e., chemical fractionation) of the solid Earth in the very early stage of the Archean, less development of light-REE enriched continental crust in the Archean, and the lower oxygen contents in the Archean atmosphere-ocean system. Finally, it is noted that Precambrian episode and protolithic features in East Asia can be understood from Precambrian orthogneiss clasts in Mesozoic Kamiaso conglomerate, since the clasts have not undergone post-depositional thermo-tectonic influences.

Journal

  • Chikyukagaku

    Chikyukagaku 34 (4), 213-223, 2000

    The Geochemical Society of Japan

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