Winchcombe: An example of rapid terrestrial alteration of a CM chondrite

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 []
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.


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