¹Johannes Lier,¹Christian Vollmer,¹Linus Risthaus,^2,3Demie Kepaptsoglou,^2,4Quentin M. Ramasse,²Aleksander B. Mosberg,⁵Ashley J. King,^5,6Charlotte L. Bays,⁵Paul F. Schofield
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70027]
¹Institut für Mineralogie, Universität Münster, Münster, Germany
²SuperSTEM Laboratory, Daresbury, UK
³School of Physics, Engineering and Technology, University of York, Heslington, UK
⁴School of Chemical and Process Engineering and School of Physics and Astronomy, University of Leeds, Leeds, UK
⁵Planetary Materials Group, Natural History Museum, London, UK
⁶Department of Earth Sciences, Royal Holloway, University of London, Egham, UK
Published by arrangement with JohnWiley & Sons

Samples of observed meteorite falls provide important constraints on alteration histories of Solar System materials. Due to its rapid collection, terrestrial alteration in the observed Mighei-type (CM) carbonaceous chondrite fall Winchcombe was minimal. In this work, the petrography and mineralogy of three Winchcombe lamellae, two from the matrix and one from a lithological clast, were analyzed by transmission electron microscopy. Our results demonstrate that the matrix of Winchcombe is dominated by Mg-Fe-rich serpentine-type phyllosilicates and tochilinite-cronstedtite intergrowth (TCI)-like phases with variable, but generally high (petrologic type 2.0–2.3) alteration degrees that agree with petrologic types acquired on TCIs on larger scales in other work. However, we also located pristine areas in investigated lamellae such as homogeneous amorphous silicates and glassy particles with sulfide and metal inclusions that resemble altered cometary GEMS (glass with embedded metal and sulfides). One distinct GEMS-like domain shows Fe-rich metal and sulfide grains with oxygen-enriched rims in a Mg-rich amorphous groundmass embedded in organic matter, which likely shielded it from more severe alteration. Fe-Ni-sulfides are mainly pentlandite and concentrated in matrix lamellae. In addition to the sub-μm scale brecciated texture, the three lamellae show different alteration extents, further demonstrating the complex alteration nature of this CM2 meteorite.

¹Sin-iti Sirono,²Diego Turrini
Scientific Reports 15, 30919 Open Access Link to Article [DOI https://doi.org/10.1038/s41598-025-12643-x]
¹Graduate School of Earth and Environmental Sciences, Nagoya University, Nagoya, Japan
²Turin Astrophysical Observatory, National Institute of Astrophysics (INAF), Pino Torinese, Italy

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