Nickeliferous pyrite tracks pervasive hydrothermal alteration in Martian regolith breccia: A study in NWA 7533 |
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| Authors: | Jean‐Pierre Lorand Roger H. Hewins Laurent Remusat Brigitte Zanda Sylvain Pont Hugues Leroux Maya Marinova Damien Jacob Munir Humayun Alexander Nemchin Marion Grange Allen Kennedy Christa Göpel |
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| Affiliation: | 1. Laboratoire de Planétologie et Géodynamique à Nantes, CNRS UMR 6112, Université de Nantes, Nantes Cédex 3, France;2. Institut 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, Paris, France;3. Department of Earth & Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA;4. Institut de Mécanique Céleste et de Calcul des Ephémérides—Observatoire de Paris—CNRS UMR 8028, Paris, France;5. Unité Matériaux et Transformations, Université Lille 1 & CNRS, Villeneuve d'Ascq, France;6. Institut Michel‐Eugène Chevreul, Université Lille 1 & CNRS, Villeneuve d'Ascq, France;7. Department of Earth Ocean & Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA;8. Department of Applied Geology, Curtin University, Perth, Western Australia, Australia;9. Institut de Physique du Globe Sorbonne Paris Cité, University Paris Diderot, Paris, France |
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| Abstract: | Martian regolith breccia NWA 7533 (and the seven paired samples) is unique among Martian meteorites in showing accessory pyrite (up to 1% by weight). Pyrite is a late mineral, crystallized after the final assembly of the breccia. It is present in all of the lithologies, i.e., the fine‐grained matrix (ICM), clast‐laden impact melt rocks (CLIMR), melt spherules, microbasalts, lithic clasts, and mineral clasts, all lacking magmatic sulfides due to degassing. Pyrite crystals show combinations of cubes, truncated cubes, and octahedra. Polycrystalline clusters can reach 200 μm in maximum dimensions. Regardless of their shape, pyrite crystals display evidence of very weak shock metamorphism such as planar features, fracture networks, and disruption into subgrains. The late fracture systems acted as preferential pathways for partial replacement of pyrite by iron oxyhydroxides interpreted as resulting from hot desert terrestrial alteration. The distribution and shape of pyrite crystals argue for growth at moderate to low growth rate from just‐saturated near neutral (6 < pH<10), H2S‐HS‐rich fluids at minimum log fO2 of >FMQ + 2 log units. It is inferred from the maximum Ni contents (4.5 wt%) that pyrite started crystallizing at 400–500 °C, during or shortly after a short‐duration, relatively low temperature, thermal event that lithified and sintered the regolith breccias, 1.4 Ga ago as deduced from disturbance in several isotope systematics. |
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