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

Jean‐pierre Lorand (1) , Jabrane Labidi (2, 3, 4) , Claire Rollion‐bard (2) , Emilie Thomassot (5) , Jeremy Bellucci (6) , Martin Whitehouse (7) , Alexander Nemchin (6) , Munir Humayun (8) , James Farquhar (4) , Roger Hewins (9) , Brigitte Zanda (9) , Sylvain Pont (9)

1 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]
2 IPGP (UMR_7154) - Institut de Physique du Globe de Paris
3 Carnegie Institution of Washington
4 University of Maryland [College Park]
5 CRPG - Centre de Recherches Pétrographiques et Géochimiques
6 Curtin University
7 NRM - Swedish Museum of Natural History
8 FSU - Florida State University [Tallahassee]
9 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie

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).

Domaines: Autre; Géochimie

Jean‐pierre Lorand, Jabrane Labidi, Claire Rollion‐bard, Emilie Thomassot, Jeremy Bellucci, et al.. The sulfur budget and sulfur isotopic composition of Martian regolith breccia NWA 7533. Meteoritics and Planetary Science, inPress, 55, pp.2097-2116. ⟨10.1111/maps.13564⟩. ⟨hal-02955751⟩