Oxygen isotope systematics of chondrules in the Paris CM2 chondrite: Indication for a single large formation region across snow line. (15th April 2021)

• Record Type: Journal Article
• Authors: Chaumard, Noël; Defouilloy, Céline; Hertwig, Andreas T.; Kita, Noriko T.
• Is Part Of: Geochimica et cosmochimica acta. Volume 299(2021)
• Page Start: 199
• Page End: 218
• Publication Date: 2021-04-15
• Subjects: Carbonaceous chondrites -- Chondrules -- Oxygen three-isotope measurements -- SIMS analyses; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2021.02.012
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: In-situ oxygen three-isotope analyses of chondrules and isolated olivine grains in the Paris (CM) chondrite were conducted by secondary ion mass spectrometry (SIMS). Multiple analyses of olivine and/or pyroxene in each chondrule show indistinguishable Δ 17 O values, except for minor occurrences of relict olivine grains (and one low-Ca pyroxene). A mean Δ 17 O value of these homogeneous multiple analyses was obtained for each chondrule, which represent oxygen isotope ratios of the chondrule melt. The Δ 17 O values of individual chondrules range from −7‰ to −2‰ and generally increase with decreasing Mg# of olivine and pyroxene in individual chondrules. Most type I (FeO-poor) chondrules have high Mg# (∼99) and variable Δ 17 O values from −7.0‰ to −3.3‰. Other type I chondrules (Mg# ≤97), type II (FeO-rich) chondrules, and two isolated FeO-rich olivine grains have host Δ 17 O values from −3‰ to −2‰. Eight chondrules contain relict grains that are either 16 O-rich or 16 O-poor relative to their host chondrule and show a wide range of Δ 17 O values from −13‰ to 0‰. The results from chondrules in the Paris meteorite are similar to those in Murchison (CM). Collectively, the Δ 17 O values of chondrules in CM chondrites continuously increase from −7‰ to −2‰ with decreasing Mg# from 99 to 37. The majority of type I chondrules (Mg# >98) show Δ 17 O values from −6‰ to −4‰, while the majority of type II chondrules (Mg# 60–70) show Δ 17 O values of −2.5‰. The covariation of Δ 17 O versus Mg# observed among chondrules in CM chondrites may suggest that most chondrules in carbonaceous chondrites formed in a single large region across the snow line where the contribution of 16 O-poor ice to chondrule precursors and dust enrichment factors varied significantly.