An electron microscopic study of gas condensates in the system Mg-Si-O-H

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概要

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• Condensates of MgSiO_3 and SiO_2 from a gas formed by evaporation of enstatite at an H_2 pressure of 4.4×10^<-10> bar and a temperature of 1525℃ by B. O. MYSEN and I. KUSHIRO (Am. Mineral. (in press), 1988) and I. KUSHIRO and B. O. MYSEN (Advances in Physical Geochemistry, New York, Springer (in press), 1988) were investigated with an analytical transmission electron microscope (ATEM), a scanning electron microscope (SEM) and an electron probe microanalyzer (EPMA). With decreasing temperature at an approximately constant total pressure the Mg/(Mg+Si) atomic ratio of the condensate (mixture of MgSiO_3 and SiO_2 polymorphs) decreases first, then increases, and finally reaches a constant value. This compositional change of the condensate is inconsistent with the equilibrium condensation model. The TEM studies suggest that metastable condensation of coesite and probably of protoenstatite and cristobalite took place. Coesite probably condensed by heterogeneous nucleation on protoenstatite. Fibrous quartz was also formed by heterogeneous nucleation on molybdenum fibers which condensed from a molybdenum vapor by a partial evaporation of a Knudsen cell used in the experiment. Heterogeneous nucleation might have played an important role in condensation process in the solar nebula. The texture of the experimental clinopyroxene condensate is different from that in interplanetary dust particles (J. P. BRADLEY et al., Nature, 301,473,1983).

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著者

• Mysen Bjorn

  Geophysical Laboratory Carnegie Institution Of Washington

• Kushiro Ikuo

  Geological Institute, Faculty of Science,University of Tokyo

• Kushiro Ikuo

  Geological Institute University Of Tokyo

• Kushiro Ikuo

  Geological Institute Faculty Of Science University Of Tokyo

• TSUCHIYAMA Akira

  Department of Earth and Space Science, Osaka University

• Morimoto Nobuo

  Department of Geology and Mineralogy, Faculty of Science, Kyoto University

• Morimoto Nobuo

  Department Of Geology And Mineralogy Faculty Of Science Kyoto University

• Tsuchiyama Akira

  Department Of Culture Osaka University

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