Shock experiments on basalt—Ferric sulfate mixes and their possible relevance to the sulfide bleb clusters in large impact melts in shergottites

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.

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