| Project/Area Number |
14340159
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | The University of Tokyo |
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Principal Investigator |
MURAKAMI Takashi The University of Tokyo, Graduate School of Science, Professor, 大学院・理学系研究科, 教授 (00253295)
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| Co-Investigator(Kenkyū-buntansha) |
KOGURE Toshihiro The University of Tokyo, Graduate School of Science, Associate Professor, 大学院・理学系研究科, 助教授 (50282728)
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥16,800,000 (Direct Cost: ¥16,800,000)
Fiscal Year 2004: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2003: ¥4,300,000 (Direct Cost: ¥4,300,000)
Fiscal Year 2002: ¥11,100,000 (Direct Cost: ¥11,100,000)
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| Keywords | Precombrian / Atmospheric evolution / Paleosol / Weathering / Mineral-water-atmosphere interaction / Dissolution rate / 黒雲母 |
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| Research Abstract |
Atmospheric oxygen concentration in the Precambrian has been intensively studied for the past decade mainly because it is closely related to the environment of the Earth's surface, especially life evolution. Paleosols, soils fowled by ancient weathering, retain the information on atmospheric oxygen at the time of weathering. Paleosols, however, were affected by later geologic events such as diagenesis and metainoiphism, and are actually metamorphic rocks. Weathering processes in the Precambrian are not well understood, and atmospheric oxygen suggested by the paleosols is not unambiguous. We carried out dissolution experiments of minerals under Precambrian atmospheric conditions, compared the results to those obtained from paleosols, and tried to clarify the mineral-water-atmosphere interactions in the Precambrian.
Dissolution experiments of Fe-rich biotite were carried out in a glove box at 1 atm of carbon dioxide partial pressure and < 3x10(-5) atm of oxygen partial pressure (anoxia experiments). For comparison, similar experiments were done under modern atmospheric conditions (oxic experiments). Fe(II) is instantaneously oxidized to form Fe(III) oxides and little Fe(II) is present in the solution in the oxic experiments. In contrast, Fe(II) is present considerably and Fe(II)-bearing vermiculite is formed in the anoxia experiments. The variations of Fe(II) and Fe(III) distributions and of Fe/Mg ratio in chlorite with depth for a 2.5 Ga paleosol are well explained by the present experimental results. Other anoxia experiments of flow-through dissolution revealed that mineral dissolution rates are faster by 3 to 4 times under anoxic conditions than oxic ones and are not affected by the presence of Fe(II) in the solution.
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