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 Delta O-17 values, except for minor occurrences of relict olivine grains (and one low-Ca pyroxene). A mean Delta O-17 value of these homogeneous multiple analyses was obtained for each chondrule, which represent oxygen isotope ratios of the chondrule melt. The Delta O-17 values of individual chondrules range from -7 parts per thousand to -2 parts per thousand 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 Delta O-17 values from -7.0 parts per thousand to -3.3 parts per thousand. Other type I chondrules (Mg# <= 97), type II (FeO-rich) chondrules, and two isolated FeO-rich olivine grains have host Delta O-17 values from -3 parts per thousand to -2 parts per thousand. Eight chondrules contain relict grains that are either O-16-rich or O-16-poor relative to their host chondrule and show a wide range of Delta O-17 values from -13 parts per thousand to 0 parts per thousand. The results from chondrules in the Paris meteorite are similar to those in Murchison (CM). Collectively, the Delta O-17 values of chondrules in CM chondrites continuously increase from -7 parts per thousand to -2 parts per thousand with decreasing Mg# from 99 to 37. The majority of type I chondrules (Mg# >98) show Delta O-17 values from -6 parts per thousand to -4 parts per thousand, while the majority of type II chondrules (Mg# 60-70) show Delta O-17 values of -2.5 parts per thousand. The covariation of Delta O-17 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 O-16-poor ice to chondrule precursors and dust enrichment factors varied significantly. (C) 2021 Elsevier Ltd. All rights reserved.