HR: 0830h
AN: V31D-0972    [PDF]
TI: Microstructures of Olivine in the Weakly Shocked Divnoe Meteorite
AU: * Ando, J
EM: ando@geol.sci.hiroshima-u.ac.jp
AF: Department of Earth and Planetary Systems Science, Hiroshima University, 1-3-1, Kagamiyama, Higashi-Hiroshima, 739-8526 Japan
AU: Tomioka, N
AF: Department of Earth and Planetary Sciences, Kobe University, 1-1, Rokkodai-cho, Nada, Kobe, 657-8501 Japan
AU: Petaev, M l
AF: Harvard-Smithsonian Center for Astrophysics and Department of Earth and Planetary Sciences, Harvard University, 60, Garden St., MS 52, Cambridge, MA 02138 United States
AU: Kanagawa, K
AF: Department of Earth Sciences, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba, 263-8522 Japan
AU: Honda, K
AF: Department of Earth and Planetary Systems Science, Hiroshima University, 1-3-1, Kagamiyama, Higashi-Hiroshima, 739-8526 Japan
AU: Shibata, Y
AF: Department of Earth and Planetary Systems Science, Hiroshima University, 1-3-1, Kagamiyama, Higashi-Hiroshima, 739-8526 Japan
AU: Yamanaka, S
AF: Department of Applied Chemistry, Hiroshima University, 1-4-1, Kagamiyama, Higashi-Hiroshima, 739-8527 Japan
AB: Many microstructural observations of minerals in meteorites show evidences of shock effect, but rarely give data about the parent body. However, the microstructures of minerals in achondrites may retain the important information about the parent body which gives a basic idea about the formation of internal structural of the Earth. We carried out microstructural and microfabric analyses of olivine grains in the Divnoe meteorite by optical microscopy, electron probe microanalysis, electron back-scattered diffraction (EBSD) analysis, and transmission electron microscopy (TEM) with the selected area electron diffraction, in order to search the microstructures produced in the parent body. The Divnoe meteorite is a granoblastic, olivine-rich primitive achondrite. Neither black shock veins nor pockets of silicate melt typical of heavily shocked meteorites were found. Most olivine grains exhibit weak undulose extinction. Some grains show mosaic extinction though this is not as pronounced as in heavily shocked meteorites, and lamellar Fe-Mg zoning (2 to 4 mole percent Fa). The weak shock metamorphism experienced by Divnoe is consistent with the shock stage S3. The EBSD analysis of the Divnoe olivine grains reveals a distinct crystallographic preferred orientation (CPO) characterized by a [001] density maximum and girdle distributions of [100] and [010] around the [001] maximum. This type of fabric is not known in crystal-plastically deformed Earths mantle rocks, and can be explained by rigid body rotation of olivines in matrix flow. It suggests that this CPO was formed by rotation of olivine grains in strong melt flows on the meteorite parent bodies, so that their longest [001] axes were aligned parallel to the flow direction. Therefore, Divnoe should preserve an initial CPO of olivine formed during crystallization in the parent body that has not been significantly disturbed by later processes such as thermal and shock metamorphism. Now, the microstructures such as dislocations and inclusions within the single crystal olivines showing the CPO which should retain the important information about the parent body are examining by TEM.
DE: 3662 Meteorites
DE: 3672 Planetary mineralogy and petrology (5410)
DE: 3924 High-pressure behavior
DE: 8147 Planetary interiors (5430, 5724)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting