Oxygen isotope systematics of chondrules in the Paris CM2 chondrite: indication for a single large formation region across snow line
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 Δ17O values, except for minor occurrences of rel...
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| Main Authors: | , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
18 February 2021
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| In: |
Geochimica et cosmochimica acta
Year: 2021, Volume: 299, Pages: 199-218 |
| ISSN: | 1872-9533 |
| DOI: | 10.1016/j.gca.2021.02.012 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1016/j.gca.2021.02.012 Verlag, lizenzpflichtig, Volltext: https://www.sciencedirect.com/science/article/pii/S0016703721000983 
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| Author Notes: | Noël Chaumard, Céline Defouilloy, Andreas T. Hertwig, Noriko T. Kita |
| Summary: | 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 Δ17O values, except for minor occurrences of relict olivine grains (and one low-Ca pyroxene). A mean Δ17O value of these homogeneous multiple analyses was obtained for each chondrule, which represent oxygen isotope ratios of the chondrule melt. The Δ17O 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 Δ17O 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 Δ17O values from −3‰ to −2‰. Eight chondrules contain relict grains that are either 16O-rich or 16O-poor relative to their host chondrule and show a wide range of Δ17O values from −13‰ to 0‰. The results from chondrules in the Paris meteorite are similar to those in Murchison (CM). Collectively, the Δ17O 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 Δ17O values from −6‰ to −4‰, while the majority of type II chondrules (Mg# 60-70) show Δ17O values of −2.5‰. The covariation of Δ17O 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 16O-poor ice to chondrule precursors and dust enrichment factors varied significantly. |
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| Item Description: | Gesehen am 19.06.2021 |
| Physical Description: | Online Resource |
| ISSN: | 1872-9533 |
| DOI: | 10.1016/j.gca.2021.02.012 |