¹Laura E. Jenkins,¹Martin R. Lee,^1,2,3Luke Daly,⁴Ashley J. King,¹Cameron J. Floyd,¹Pierre-Etienne Martin,⁴Natasha V. Almeida,⁵Matthew J. Genge
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13949]
¹School of Geographical and Earth Sciences, The University of Glasgow, Glasgow, G12 8RZ UK
²Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, 6845 Australia
³Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, New South Wales, 2006 Australia
⁴Planetary Materials Group, Natural History Museum, London, SW7 5BD UK
⁵Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ UK
Published by arrangement with John Wiley & Sons

Winchcombe is a CM chondrite that fell in England on February 28, 2021. Its rapid retrieval was well characterized. Within two polished sections of Winchcombe, terrestrial phases were observed. Calcite and calcium sulfates were found in a sample recovered from a field on March 6, 2021, and halite was observed on a sample months after its recovery from a driveway on March 2, 2021. These terrestrial phases were characterized by scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. Calcite veins crosscut the fusion crust and therefore postdate it. The calcite likely precipitated in the damp environment (sheep field) where the meteorite lay for six days prior to its retrieval. The sulfates occur on the edges of the sample and were identified as three minerals: gypsum, bassanite, and anhydrite. Given that the sulfates occur only on the sample’s edges, including on top of the fusion crust, they formed after Winchcombe fell. Sulfate precipitation is attributed to the damp fall environment, likely resulted from sulfide-derived H2S reacting with calcite within the meteorite. Halite occurs as euhedral crystals only on the surface of a polished section and exclusively in areas relatively enriched in sodium. It was likely produced by the interaction of the polished rock slice with the humid laboratory air over a period of months. The sulfates, fusion crust calcite, and halite all post-date Winchcombe’s entry into the Earth’s atmosphere and showcase how rapidly meteorite falls can be terrestrially altered.

^1,2Guy Libourel,²Kazuhide Nagashima,³Marc Portail,²Alexander N. Krot
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.01.026]
¹Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
²Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96821, USA
³CNRS-CRHEA (Centre de Recherches sur l’Hétéro-Epitaxie et ses Applications), Université Côte d’Azur, Sophia Antipolis, Rue Bernard Grégory, 06560 Valbonne, France
Copyright Elsevier

Oxygen-isotope studies of carbonaceous chondrite chondrules are of pivotal importance for understanding of the evolution of the solar protoplanetary disk. It has been previously concluded that the observed variations in Δ17O (= δ17O – 0.52×δ18O) of chondrule olivines and pyroxenes are intimately tied to their Mg# (= MgO/(MgO+FeO) ×100, mol%) and the inferred oxygen fugacity (fO2) of gaseous reservoirs produced by evaporation of disk regions with different (silicate dust ± water ice)/gas ratios. Using high resolution cathodoluminescence and secondary ion mass spectrometry, we show, in contrast to host chondrule data, that Δ17O of chondrule olivines from the Yamato 81020 CO3.05 carbonaceous chondrite is independent of their Mg# and of the imposed fO2. Instead, there is a Δ17O bimodal distribution of Mg-rich olivines that gradually turns into a unimodal distribution as Mg# decreases. We suggest that chondrules recorded an evolution of an isotopically heterogeneous vapor plume resulting from a high temperature mixing of the 16O-enriched (Δ17O ≈ −6±2‰) and 16O-depleted (Δ17O ≈ −2.5±1‰) reservoirs. Drop in the vapor plume temperature under unbuffered redox conditions favors the dissolution of Fe,Ni-metal of chondrules and the subsequent crystallization of FeO-rich olivines at saturation; the 16O-depleted signature being the most resilient at lower temperature. Chondrules are thus inferred to have formed in a same turbulent heterogeneous environment in which locally high temperatures and reducing conditions prevailed (Type I), adjacent in space and/or in time to areas submitted to lower temperatures and more oxidizing conditions (Type II). Subtracting of chondrules at different stages of the gaseous plume evolution by fast cooling rates give rise to the chemical and isotopic diversity of chondrules. No extrinsic oxidizing agents (e.g., water ice) are needed in this scenario.