To be or not to be oxidized: A case study of olivine behavior in the fusion crust of ureilite A 09368 and H chondrites A 09004 and A 09502

1Lidia Pittarello,2,3Akira Yamaguchi,4Julia Roszjar,5Vinciane Debaille,1,4Christian Koeberl,6Philippe Claeys
Meteoritics & Planetary Science (in Press) Link to Article []
1Department of Lithospheric Research, University of Vienna, Althanstraße 14, A‐1090 Vienna, Austria
2National Institute of Polar Research, 10‐3 Midori‐cho, Tachikawa, Tokyo, 190‐8518 Japan
3Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, 190‐8518 Japan
4Natural History Museum Vienna, Burgring 7, A‐1010 Vienna, Austria
5Laboratoire G‐Time (Géochimie: Traçage isotopique, minéralogique et élémentaire), Université Libre de Bruxelles, Av. F.D., Roosevelt 50, 1050 Brussels, Belgium
6Analytical, Environmental and Geo‐Chemistry (AMGC), Vrije Universiteit Brussel, Pleinlaan 2, B‐1050 Brussels, Belgium
Published by arrangement with John Wiley & Sons

Meteorite fusion crusts are quenched melt layers formed during meteoroid atmospheric entry, mostly preserved as coating on the meteorite surface. Antarctic ureilite Asuka (A) 09368 and H chondrites A 09004 and A 09502 exhibit well preserved thick fusion crusts, characterized by extensive olivine crystallization. As olivine is one of the major components of most meteorites and its petrologic behavior is well constrained, it can be roughly considered as representative for the bulk meteorite. Thus, in this work, the evolution of olivine in fusion crusts of the above‐listed selected samples is investigated. The different shape and chemistry of olivine crystallized in the fusion crust, both as overgrown rim on relic olivine clasts and as new crystals, suggest a general temperature and cooling rate gradient. The occurrence of reverse and oscillatory zoning in individual olivine grains within the fusion crust suggests complex redox reactions. Overall, the investigated fusion crusts exhibit a general oxidation of the relatively reduced initial material. However, evidence of local reduction is preserved. Reduction is likely triggered by the presence of carbon in the ureilite or by overheating during the atmospheric entry. Constraining these processes provides a potential analog for interpreting features observed in cosmic spherules and micrometeorites and for calibrating experiments and numerical models on the formation of fusion crusts.


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