Iron oxidation state of a 2.45-Byr-old paleosol developed on mafic volcanics

Satoshi Utsunomiya, Takashi Murakami, Masami Nakada, Takeshi Kasama

研究成果: ジャーナルへの寄稿学術誌査読

37 被引用数 (Scopus)

抄録

The 2.45-Byr-old weathering profile developed on early Proterozoic mafic volcanics located near Cooper Lake, Ontario, Canada, was examined geochemically and mineralogically for a better understanding of the atmospheric oxygen evolution. Ferrous to ferric ion, Fe(II) and Fe(III), respectively, ratios of the bulk rock samples were analyzed by Mössbauer spectrometry. The total Fe (Fe(T)) and Fe(II) concentrations decrease from 12.0 and 11.2 wt.% to 1.85 and 0.89 wt.%, respectively, from the bottom to the top of the weathering profile. The Fe(T) and Fe(II) concentrations normalized to Ti and Zr, as well as the Fe(II)/Fe(III) ratio of raw data, linearly decrease with depth toward the top, while the Fe(III) concentration remains nearly constant throughout the profile. The linear decrease of Fe(II), accompanied by the nearly constant distribution of Fe(III), is difficult to be explained by the scenario of oxidizing weathering and subsequent reducing hydrothermal alteration. The behaviors of Fe(II) and Fe(III) can be simply explained by anoxic weathering. The anoxic weathering suggests that the 2.45-Ga atmosphere was anoxic. The slight increase of Fe/(Fe) in the octahedral sites of chlorite toward the top and no Ce anomaly in the REE patterns are also consistent with anoxic weathering.

本文言語英語
ページ(範囲)213-221
ページ数9
ジャーナルGeochimica et Cosmochimica Acta
67
2
DOI
出版ステータス出版済み - 1月 15 2003
外部発表はい

!!!All Science Journal Classification (ASJC) codes

  • 地球化学および岩石学

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