Thermal history of ureilite, Pecora Escarpment 82506 deduced from cation distribution and diffusion profile of minerals
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概要
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PCA82506 is relatively unshocked compared with most ureilites. Large unshocked pigeonite and olivine crystals were studied by means of single crystal X-ray diffraction, analytical TEM, optical microscope and an electronprobe. The chemical compositions of the PCA82506 pigeonites are (Ca)_6(Mg)_<76>(Fe)_<18>, while the average olivine core composition is (Fa)_<20>. A region about 50 micrometer apart from the olivine rim is reduced by the carbonaceous (C) matrix. From the diffusion profiles of olivine crystals, a cooling rate of 10-15℃/h is estimated by the computer simulation method of MIYAMOTO et al. (Proc. Lunar Planet. Sci. Conf., 16th, Pt. 1,D116,1985). The cell dimensions of the PCA82506 pigeonite determined from 23 reflections are : a, 9.6649(9); b, 8.8719(6); c, 5.2134(5)A; and β, 108.51(6)°. The site occupancy factors are M1 (Mg 0.064,Fe 0.936) and M2 (Ca 0.116,Mg 0.568,Fe 0.316). This cation distribution gives an equilibrium temperature of 800℃ by plotting the K value of PCA82506 on the distribution isotherm of SAXENA et al. (Earth Planet. Sci. Lett., 21,194,1974). The PCA82506 pigeonites may have cooled more rapidly than terrestrial pigeonites from the Isle of Mull and almost as rapid as the most rapidly cooled mare basalts.
- 国立極地研究所の論文
著者
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Takeda Hiroshi
Mineralogical Institute, University of Tokyo
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Ishii Teruaki
Ocean Research Institute The University Of Tokyo
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Ishii Teruaki
Ocean Research Institute University Of Tokyo
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Haga Nobuhiko
Mineralogical Institute Faculty Of Sciences University Of Tokyo
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Tachikawa Osamu
Mineralogical Institute Faculty Of Science University Of Tokyo
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Tachikawa Osamu
Mineralogical Institute Faculty Of Sciences University Of Tokyo
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Toyoda Hiromi
Mineralogical Institute, Faculty of Sciences, University of Tokyo
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Toyoda Hiromi
Mineralogical Institute Faculty Of Sciences University Of Tokyo
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Takeda Hiroshi
Mineralogical Institute Faculty Of Science University Of Tokyo
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Takeda Hiroshi
Mineralogical Institute Faculty Of Sciences University Of Tokyo
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