Microstructures of Olivine in the Weakly Shocked Divnoe Meteorite

Details Microstructures of Olivine in the Weakly Shocked Divnoe Meteorite Microstructures of Olivine in the Weakly Shocked Divnoe Meteorite

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.v31d0972a&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #V31D-0972

Physics

3662 Meteorites, 3672 Planetary Mineralogy And Petrology (5410), 3924 High-Pressure Behavior, 8147 Planetary Interiors (5430, 5724)

Scientific paper

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.

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