Research Field
Environmental Mineralogy
Current Research
My group's main interest is clarifying the interactions of mineral-water-atmosphere. The interactions at the Earth's surface have played a major role in the evolution of the atmosphere and ocean, and in the transport and cycle of an element, and are recorded in minerals through weathering and alteration. We have been analyzing the fine and local structures of such minerals in order to clarify the fundamental processes, kinetics, and mechanisms of the mineral-water-atmosphere interactions. The fundamental processes are examined up to the atomic scale mainly by transmission electron microscopy. The fundamental processes, kinetics, and mechanisms may be applied to element transport and Precambrian weathering. Thus the interactions can be understood in a wide range of the space(microscopic to macroscopic) and the time (the Precambrian to modern).
The main research programs of our group are:(1) Laboratory and field experiments of dissolution and weathering of silicate minerals, and the effects of dissolution and weathering on element transport, and(2) Precambrian weathering and its relation to the atmospheric evolution.
For the former, we are especially interested in feldspars and mafic sheet silicates because feldspars occur commonly at the Earth's surface and the feldspar-water interactions are closely related to the consumption of the atmospheric carbon dioxide, and mafic sheet silicates such as biotite and chlorite are the source of Mg and Fe in clays and the dissolution mechanisms are unique.We recently found that feldspar weathering in nature is controlled by saturation state and the formation of secondary minerals by transmission electron microscopic observation and thermodynamic calculation. We also found that mafic sheet silicates are changed to different sheet silicates layer by layer and then dissolve in natural weathering. We modelled the transport of U during weathering and quantitatively showed the redistribution of U in the size of about 200 meters and in the time of 2 million years.For the latter, we are interested in the processes, kinetics, and mechanisms of weathering under high partial pressure of carbon dioxide and low partial pressure of oxygen. We have rock samples that were weathered 3.5-1.7 billion years ago.The examination of Precambrian weathering will show how carbon dioxide decreased and oxygen increased in the atmosphere.We recently found a direct weathering product, rhabdophane, from 2.5 billion years old granite. The rhabdophane contains a significant amount of Ce, which indicates that Ce was behaved as Ce(3+) in groundwater like La(3+) and Nd(3+), that is, the oxygen concentration in the atmosphere was quite low 2.5 billion years ago.
Representative Publications
1. Murakami, T., J. Ito, S. Utsunomiya, T. Kasama, N. Kozai, T. Ohnuki, Anoxic dissolution processes of biotite: implications for Fe behavior during Archean weathering, Earth and Planetary Science Letters 224, 117-129, 2004.
2. Murakami, T., S. Utsunomiya, Y. Imazu, N. Prasad, Direct evidence of late Archean to early Proterozoic anoxic atmosphere from a product of 2.5 Ga old weathering, Earth and Planetary Science Letters, 184, 523-528, 2001.
3. Murakami, T., S. Utsunomiya, T. Yokoyama, T. Kasama, Biotite dissolution processes and mechanisms in the laboratory and in nature: Early stage weathering environment and vermiculitization, American Mineralogist, 88, 377-386, 2003.
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