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Mass-Independent Oxygen Isotopic Partitioning During Gas-Phase SiO2 Formation

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Science  25 Oct 2013:
Vol. 342, Issue 6157, pp. 463-466
DOI: 10.1126/science.1242237

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Explaining Anomalous Early Isotopes

Meteorites contain some of the oldest materials formed in the solar system, including silicate minerals similar in composition to those on Earth. These meteorites, however, often differ in their oxygen isotopic composition, implying that their formation involved a different chemical mechanism than younger solar-system materials. Chakraborty et al. (p. 463) performed a series of experiments and found that mixing of SiO gas and OH leads to a mass-independent isotope fractionation in SiO2 solid products similar to those observed in the oldest meteorites. This oxidation reaction may thus have served as the first source for silicates with anomalous oxygen isotopic compositions in the solar nebula.

Abstract

Meteorites contain a wide range of oxygen isotopic compositions that are interpreted as heterogeneity in solar nebula. The anomalous oxygen isotopic compositions of refractory mineral phases may reflect a chemical fractionation process in the nebula, but there are no experiments to demonstrate this isotope effect during particle formation through gas-phase reactions. We report experimental results of gas-to-particle conversion during oxidation of silicon monoxide that define a mass-independent line (slope one) in oxygen three-isotope space of 18O/16O versus 17O/16O. This mass-independent chemical reaction is a potentially initiating step in nebular meteorite formation, which would be capable of producing silicate reservoirs with anomalous oxygen isotopic compositions.

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