Oxygen isotope systematics of chondrule olivine, pyroxene, and plagioclase in one of the most pristine CV3Red chondrites (Northwest Africa 8613)

1,3Andreas T. Hertwig,2Makoto Kimura,1Céline Defouilloy,1Noriko T. Kita
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13379]
1WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA 2
2National Institute of Polar Research, Meteorite Research Center, Midoricho 10-3, Tachikawa Tokyo 190-8518, Japan 3
3Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles,
Los Angeles, California 90095, USA
Published by arrangement with John Wiley & Sons

We performed in situ oxygen three-isotope measurements of chondrule olivine,pyroxenes, and plagioclase from the newly described CVRedchondrite NWA 8613.Additionally, oxygen isotope ratios of plagioclase in chondrules from the Kaba CV3OxBchondrite were determined to enable comparisons of isotope ratios and degree of alterationof chondrules in both CV lithologies. NWA 8613 was affected by only mild thermalmetamorphism. The majority of oxygen isotope ratios of olivine and pyroxenes plot along aslope-1 line in the oxygen three-isotope diagram, except for a type II and a remolten barredolivine chondrule. When isotopic relict olivine is excluded, olivine, and low- and high-Capyroxenes are indistinguishable regardingD17O values. Conversely, plagioclase in chondrulesfrom NWA 8613 and Kaba plot along mass-dependent fractionation lines. Oxygen isotopicdisequilibrium between phenocrysts and plagioclase was caused probably by exchange ofplagioclase with16O-poor fluids on the CV parent body. Based on an existing oxygenisotope mass balance model, possible dust enrichment and ice enhancement factors wereestimated. Type I chondrules from NWA 8613 possibly formed at moderately high dustenrichment factors (509to 1509CI dust relative to solar abundances); estimates for waterice in the chondrule precursors range from 0.29to 0.69the nominal amount of ice in dustof CI composition. Findings agree with results from an earlier study on oxygen isotopes inchondrules of the Kaba CV chondrite, providing further evidence for a relatively dry andonly moderately high dust-enriched disk in the CV chondrule-forming region.


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