A super‐refractory inclusion containing nonstoichiometric spinel from the CO3.0 chondrite Yamato 81020

1Hisayoshi Yurimoto,2Alan E. Rubin,3Shoichi Itoh,4John T. Wasson
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13652]
1Isotope Imaging Laboratory (IIL), Natural History Sciences, Hokkaido University, Sapporo, 001–0021 Japan
2Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, 90095–1567 USA
3Department of Earth and Planetary Sciences, Kyoto University, Kyoto, 606–8502 Japan
4Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, 90095–1567 USA
Published by arrangement with John Wiley & Sons

We studied a unique super‐refractory inclusion with a core‐mantle structure from CO3.0 Yamato 81020 by secondary ion mass spectrometry, electron microprobe, and scanning electron microscope techniques. The core consists largely of hibonite and nonstoichiometric Al‐rich spinel indicating formation as a liquid at an exceptionally high temperature (>1900 °C). The mantle consists almost entirely of melilite with gehlenitic compositions (ranging from Åk2 to Åk25). The oxygen‐ and magnesium‐isotopic compositions of the core and mantle are very different; typically, Δ17O (≡δ17O − 0.52 δ18O) ~–26‰ and ƒMg (mass fractionation of Mg isotopes) ~10‰/amu in the core and Δ17O ~–7‰ and ƒMg ~1‰/amu in most of the mantle. The chemical and O, Mg‐isotopic data indicate that the core and mantle formed in separate events, and that the melilite now in the core was formed during the mantle‐melting event, probably filling preexisting voids and surficial cavities. Analyses of core and mantle phases plot along a single 26Al‐26Mg isochron with initial (26Al/27Al)0 corresponding to 4.8 ± 1.0 (±2σ) × 10–5, suggesting a similar formation age to normal CAIs in chondrites.

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