Nickeliferous pyrite tracks pervasive hydrothermal alteration in Martian regolith breccia: A study in NWA 7533

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...

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Bibliographic Details
Published in:Meteoritics & planetary science 2015-12, Vol.50 (12), p.2099-2120
Main Authors: Lorand, Jean-Pierre, Hewins, Roger H., Remusat, Laurent, Zanda, Brigitte, Pont, Sylvain, Leroux, Hugues, Marinova, Maya, Jacob, Damien, Humayun, Munir, Nemchin, Alexander, Grange, Marion, Kennedy, Allen, Göpel, Christa
Format: Article
Language:English
Subjects:
Alterations
Breccia
Crystallization
Crystals
Earth Sciences
Fracture mechanics
Mars surface
Planetology
Pyrite
Regolith
Sciences of the Universe
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Summary: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 
ISSN:1086-9379
1945-5100
DOI:10.1111/maps.12565