Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29s.483k&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 483-484
Computer Science
Chemical Composition, Chondrites, Meteoritic Composition, Perovskites, Abundance, Cores, Petrology, Rims, Spinel
Scientific paper
A petrographic and electron probe microanalysis (EPMA) study revealed the presence of different populations of perovskites and hibonites in Ca-Al rich inclusions (CAIs) from the Yamato-791601 CV3 chondrite. Some of them are probably of extraneous origin. This CAI (YM1) is very large and has a core-mantle structure. The core consists mainly of loosely packed coarse spinels with anorthite, fassaite, diopside and grossular in their interstices. The mantle consists of melilite with minor populations of spinel, hibonite and perovskite. A few euhedral grains of corundum, several micrometers in size, are found in the melilite mantle. The narrow rims are developed as successive layers on the outermost mantle. In thin section YM1 is quadrilateral in shape and lacks mantle and rim in both elongated sides. It seems that the spinel core lies between the two mantles. The mineral assemblage resembles type A CAI (CTA); however, the abundance of spinel and melilite and the textural features differ from type A. Three distinct populations of hibonites were encountered in the rim sequence, in spinel framboids, and in captured multiphase fragments. Hibonites in captured fragments are rich in V2O3. In contrast, hibonites in spinel framboids are depleted in V2O3. These hibonites display a positive correlation between V2O3 and TiO2 contents. This result suggests that the hibonite populations originated from different sources. There are three categories of perovskites: grains in the rim sequence, as a composite grain, and subhedral grains in the melilite mantle. Perovskites forming the innermost rim with spinel and hibonite are heterogeneously distributed. The composite grain is amoeboid in shape and consists of a bright and a dark portion on BEI image. Perovskites in the rims show a negative relationship between Y2O3 and ZrO2 and mainly belong to type 1.
El Goresy Ahmed
Kojima Hedeyasu
Yanai Keizo
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