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Oxygen isotope systematics of chondrule olivine, pyroxene, and plagioclase in one of the most pristine CV 3 Red chondrites (Northwest Africa 8613)
Author(s) -
Hertwig Andreas T.,
Kimura Makoto,
Defouilloy Céline,
Kita Noriko T.
Publication year - 2019
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.13379
Subject(s) - chondrule , plagioclase , chondrite , olivine , isotopes of oxygen , pyroxene , geology , geochemistry , phenocryst , meteorite , parent body , astrobiology , quartz , physics , paleontology
We performed in situ oxygen three‐isotope measurements of chondrule olivine, pyroxenes, and plagioclase from the newly described CV R ed chondrite NWA 8613. Additionally, oxygen isotope ratios of plagioclase in chondrules from the Kaba CV 3 OxB chondrite were determined to enable comparisons of isotope ratios and degree of alteration of chondrules in both CV lithologies. NWA 8613 was affected by only mild thermal metamorphism. The majority of oxygen isotope ratios of olivine and pyroxenes plot along a slope‐1 line in the oxygen three‐isotope diagram, except for a type II and a remolten barred olivine chondrule. When isotopic relict olivine is excluded, olivine, and low‐ and high‐Ca pyroxenes are indistinguishable regarding Δ 17 O values. Conversely, plagioclase in chondrules from NWA 8613 and Kaba plot along mass‐dependent fractionation lines. Oxygen isotopic disequilibrium between phenocrysts and plagioclase was caused probably by exchange of plagioclase with 16 O‐poor fluids on the CV parent body. Based on an existing oxygen isotope mass balance model, possible dust enrichment and ice enhancement factors were estimated. Type I chondrules from NWA 8613 possibly formed at moderately high dust enrichment factors (50× to 150× CI dust relative to solar abundances); estimates for water ice in the chondrule precursors range from 0.2× to 0.6× the nominal amount of ice in dust of CI composition. Findings agree with results from an earlier study on oxygen isotopes in chondrules of the Kaba CV chondrite, providing further evidence for a relatively dry and only moderately high dust‐enriched disk in the CV chondrule‐forming region.