The sulfur budget and sulfur isotopic composition of Martian regolith breccia NWA 7533

1Jean‐Pierre Lorand2,3,4Jabrane Labidi,4Claire Rollion‐Bard,5Emilie Thomassot,6Jeremy J. Bellucci,7Martin Whitehouse,7Alexander Nemchin,8Munir Humayun,3James Farquhar,9,10Roger H. Hewins,9Brigitte Zanda,9Sylvain Pont
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13564]
1Laboratoire de Planétologie et Géodynamique à Nantes, CNRS, UMR 6112, Université de Nantes, 2 Rue de la Houssinère, BP 92208, 44322 Nantes Cédex 3, France
2Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, 20015 USA
3Department of Geology, University of Maryland, College Park, Maryland, 20740 USA
4Institut de physique du globe de Paris, CNRS, Université de Paris, F‐75005 Paris, France
5CRPG‐CNRS, Nancy, 54500 France
6Department of Applied Geology, Curtin University, Perth, Western Australia, 6845 Australia
7Laboratory for Isotope Geology, Swedish Mus. of Nat History, Stockholm, SE‐104 05 Sweden
8Department of Earth, Ocean & Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, 32310 USA
9Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC) ‐ Sorbonne, Université‐ Muséum National d’Histoire Naturelle, UPMC Université Paris 06, UMR CNRS 7590, IRD, UMR 206, 61 rue Buffon, 75005 Paris, France
10Department of Earth & Planetary Sciences, Rutgers University, Piscataway, New Jersey, 08854 USA
Published by arrangement with John Wiley & Sons

The sulfur isotope budget of Martian regolith breccia (NWA 7533) has been addressed from conventional fluorination bulk rock analyses and ion microprobe in situ analyses. The bulk rock analyses yield 865 ± 50 ppm S in agreement with LA‐ICP‐MS analyses. These new data support previous estimates of 80% S loss resulting from terrestrial weathering of NWA 7533 pyrite. Pyrite is by far the major S host. Apatite and Fe oxyhydroxides are negligible S carriers, as are the few tiny igneous pyrrhotite–pentlandite sulfide grains included in lithic clasts so far identified. A small nonzero Δ33S (−0.029 ± 0.010‰) signal is clearly resolved at the 2σ level in the bulk rock analyses, coupled with negative CDT‐normalized δ34S (−2.54 ± 0.10‰), and near‐zero Δ36S (0.002 ± 0.09‰). In situ analyses also yield negative Δ33S values (−0.05 to −0.30‰) with only a few positive Δ33S up to +0.38‰. The slight discrepancy compared to the bulk rock results is attributed to a possible sampling bias. The occurrence of mass‐independent fractionation (MIF) supports a model of NWA 7533 pyrite formation from surface sulfur that experienced photochemical reaction(s). The driving force that recycled crustal S in NWA 7533 lithologies—magmatic intrusions or impact‐induced heat—is presently unclear. However, in situ analyses also gave negative δ34S values (+1 to −5.8‰). Such negative values in the hydrothermal setting of NWA 7533 are reflective of hydrothermal sulfides precipitated from H2S/HS‐ aqueous fluid produced via open‐system thermochemical reduction of sulfates at high temperatures (>300 °C).

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