Other
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998m%26ps...33.1169h&link_type=abstract
Meteoritics & Planetary Science, vol. 33, no. 5, pp. 1169-1179
Other
9
Scientific paper
Two types of mesostasis co-exist within some porphyritic chondrules in Tieschitz. One type is smooth. The other, confined to chondrule margins, is blocky on a 5-10 micron scale. Mesostases in one POP chondrule and one PO chondrule were analysed by SEM/EDS, as was white matrix nearby. Mesostases in the PO chondrule and in four others were analysed by ion-probe. Pyroxene phenocrysts or dendrites extend across contacts between smooth and blocky mesostasis with no compositional change. Relative to smooth mesostasis, blocky mesostasis is enriched in Al, alkalis, Ba, F and Cl but depleted in Si, Fe and Ca. White matrix fills channels between the chondrules. It is physically and chemically similar to blocky mesostasis, but three ion-probe analyses indicate that, unlike the mesostases it is poor in Sc and has variable and fractionated REEs. Smooth mesostasis is interpreted as solidified primary chondrule liquid, whereas blocky is its alteration product or, less likely, a precipitate replacing smooth mesostasis leached out by aqueous fluid. White matrix may have formed by secondary alteration or replacement of mesostases that had been expelled from chondrules during accretion, or as a precipitate filling interchondrule voids. Iron may have been lost from the bulk meteorite, but most other elements merely underwent internal redistribution. Disturbed isotopic systems indicate that aqueous fluid may have been active on the Tieschitz parent body only 2 Ga ago. If correct, this would be the first evidence that an ordinary chondrite parent body underwent internal reprocessing significantly later than 4.5 Ga ago.
Bridges John C.
Hutchison Robert
O'D. Alexander Conel M.
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