Evidence for the presence of chondrule‐ and CAI‐derived material in an isotopically anomalous Antarctic micrometeorite

1,2Bastien Soens,3,4Martin D. Suttle,1Ryoga Maeda,5Frank Vanhaecke,6Akira Yamaguchi,7Matthias Van Ginneken,2Vinciane Debaille,1Philippe Claeys,1Steven Goderis
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13599]
1Analytical‐, Environmental‐, and Geo‐Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, Brussels, 1050 Belgium
2Laboratoire G‐Time, Université Libre de Bruxelles 50, Av. F.D. Roosevelt CP 160/02, Brussels, 1050 Belgium
3Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, Pisa, 56126 Italy
4Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD UK
5Atomic & Mass Spectrometry – A&MS Research Group, Department of Chemistry, Ghent University, Krijgslaan 218 – S12, Ghent, 9000 Belgium
6National Institute of Polar Research, 10‐3 Midori‐cho, Tachikawa‐shi, Tokyo, 190‐8518 Japan
7Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, Kent, CT2 7NZ UK
Published by arrangement with John Wiley & Sons

We report the discovery of a unique, refractory phase‐bearing micrometeorite (WF1202A‐001) from the Sør Rondane Mountains, East Antarctica. A silicate‐rich cosmic spherule (~400 µm) displays a microporphyritic texture containing Ca‐Al‐rich inclusion (CAI)‐derived material (~5–10 area%), including high‐Mg forsterite (Fo98‐99) and enstatite (En98‐99, Wo0‐1). The micrometeorite also hosts a spherical inclusion (~209 µm), reminiscent of chondrules, displaying a barred olivine texture. Oxygen isotopic compositions of the micrometeorite groundmass (δ17O = –3.46‰, δ18O = 10.43‰, ∆17O = –1.96‰) are consistent with a carbonaceous chondrite precursor body. Yet, a relict forsterite grain is characterized by δ17O = –45.8‰, δ18O = –43.7‰, ∆17O = –23.1‰, compatible with CAIs. In contrast, a relict low‐Ca pyroxene grain (δ17O = –4.96‰, δ18O = –4.32‰, ∆17O = –2.71‰) presumably represents a first‐generation silicate grain that accreted 18O‐rich gas or dust in a transient melting scenario. The spherical inclusion displays anomalous oxygen isotope ratios (δ17O = –0.98‰, δ18O = –2.16‰, ∆17O = 0.15‰), comparable to anhydrous interplanetary dust particles (IDPs) and fragments from Comet 81P/Wild2. Based on its major element geochemistry, the chondrule size, and oxygen isotope systematics, micrometeorite WF1202A‐001 likely sampled a carbonaceous chondrite parent body similar to, but distinct from CM, CO, or CV chondrites. This observation may suggest that some carbonaceous chondrite bodies can be linked to comets. The reconstructed atmospheric entry parameters of micrometeorite WF1202A‐001 suggest that the precursor particle originated from a low‐inclination, low‐eccentricity source region, most likely either the main belt asteroids or Jupiter family comets (JFCs).


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