¹M. N. Rao,²L. E. Nyquist,³P. D. Asimow,^4,5D. K. Ross,^6,7S. R. Sutton,⁸T. H. See,⁴C. Y. Shih,⁴D. H. Garrison,⁹S. J. Wentworth,¹⁰J. Park
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13770]
¹SCI, Johnson Space Center, Houston, Texas, 77058 USA
²XI, NASA, Johnson Space Center, Houston, Texas, 77058 USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
⁴Jacobs JETS, NASA, Johnson Space Center, Houston, Texas, 77058 USA
⁵UTEP-CASSMAR, El Paso, Texas, 79968 USA
⁶Department of Geophysical Sciences, University of Chicago, Chicago, Illinois, 60439 USA
⁷CARS, Argonne National Laboratory, Argonne, Illinois, 60439 USA
⁸Barrios Technology/Jacobs JETS, NASA, Johnson Space Center, Houston, Texas, 77058 USA
⁹HEPCO, Jacobs JETS, NASA Johnson Space Center, Houston, Texas, 77058 USA
¹⁰Kingsborough Community College, Brooklyn, New York, 11235 USA
Published by arrangement with John Wiley & Sons

Large impact-melt pockets in shergottites contain both Martian regolith components and sulfide/sulfite bleb clusters that yield high sulfur concentrations locally compared to bulk shergottites. The regolith may be the source of excess sulfur in the shergottite melt pockets. To explore whether shock and release of secondary Fe-sulfates trapped in host rock voids is a plausible mechanism to generate the shergottite sulfur bleb clusters, we carried out shock recovery experiments on an analog mixture of ferric sulfate and Columbia River basalt at peak pressures of 21 and 31 GPa. The recovered products from the 31 GPa experiment show mixtures of Fe-sulfide and Fe-sulfite blebs similar to the sulfur-rich bleb clusters found in shergottite impact melts. The 21 GPa experiment did not yield such blebs. The collapse of porosity and local high-strain shear heating in the 31 GPa experiment presumably created high-temperature hotspots (~2000 °C) sufficient to reduce Fe3+ to Fe2+ and to decompose sulfate to sulfite, followed by concomitant reduction to sulfide during pressure release. Our results suggest that similar processes might have transpired during shock production of sulfur-rich bleb clusters in shergottite impact melts. It is possible that very small CO presence in our experiments could have catalyzed the reduction process. We plan to repeat the experiments without CO.

¹J.-C.Viennet,²C.Le Guillou,¹L.Remusat,³F.Baron,¹L.Delbes,²A.M.Blanchenet,¹B.Laurent,¹I.Criouet,¹S.Bernard
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.12.002]
¹Muséum National d’Histoire Naturelle, Sorbonne Université, UMR CNRS 7590, Institut de minéralogie, de physique des matériaux et de cosmochimie, Paris, France
²Univ. Lille, CNRS, INRA, ENSCL, UMR 8207 – UMET – Unité Matériaux et Transformations, F-59000 Lille, France
³Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), UMR 7285 CNRS, Université de Poitiers, F-86073 Poitiers Cedex 9, France
Copyright Elsevier

Carbonaceous chondrites contain both soluble and insoluble organic materials (SOM and IOM) which may have been produced in different environments via different processes or share possible genetic relationships. The SOM may have been produced from IOM during hydrothermal episodes on asteroids, and vice versa. The potential role played by the mineral matrix during these episodes (clay minerals of variable crystallinity) remains to be constrained. Here, we exposed a mixture of formaldehyde and glycolaldehyde with ammonia-bearing liquid water together with Fe-rich smectitic minerals to hydrothermal conditions mimicking asteroidal conditions. We used both amorphous gel of smectite or crystalline smectites in order to understand the influence of the crystallinity on the evolution of OM. The organo-mineral experimental residues were characterized at a multiple length scales using X-ray diffraction and microscopy/spectroscopic tools. Results evidence that some IOM polymerizes/condenses in the absence of Fe-rich smectites. Yet, the presence of Fe-rich smectites inhibits this production of IOM. Indeed, the interactions between the SOM and clay surfaces (interlayers or edges) reduce the concentration of SOM available for polymerization/condensation reactions, a necessary step for the production of IOM. In addition, the presence of OM disorganizes the crystallization of the Fe-rich amorphous silicates, leading to smaller crystal sized particles exhibiting a lower permanent charge. This might suggests that the smectite permanent charge distribution may help better constraining the origin and evolution of chondritic clay minerals. Altogether, the present study sheds new light on the organo-mineral interactions having occurred during hydrothermal episodes onto/within chondritic asteroids. Indeed, IOM formation from OM-rich aqueous fluids does not occur during the alteration of amorphous silicates. This would mean that IOM is either produced within pockets free of clay minerals or initially accreted as IOM-rich grain. Last, about ∼50 wt.% of the initial C could not be removed from the clay minerals at the end of the experiments using classical solvent extraction protocols, demonstrating that a high fraction of the SOM in carbonaceous chondrites may have been overlooked.