¹Brendan J. Orenstein,^2,3,4Michael W.M. Jones,¹David T. Flannery,⁵Austin P. Wright,⁶Scott Davidoff,⁷Michael M. Tice,¹Luke Nothdurft,¹Abigail C. Allwood
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116202]
¹School of Earth and Atmospheric Sciences, Queensland University of Technology, Brisbane, QLD 4000, Australia
²Central Analytical Research Facility, Queensland University of Technology, Brisbane, QLD 4000, Australia
³School of Chemistry and Physics, Queensland University of Technology, Brisbane, QLD 4000, Australia
⁴Centre for Materials Science, Queensland University of Technology, Brisbane, QLD 4000, Australia
⁵School of Computational Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
⁶Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
⁷Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, USA
Coypright Elsevier

Elemental quantification instruments for planetary missions provide a capability for in-situ identification of mineral phases via stoichiometry, an essential step in petrological investigations. X-ray fluorescence (XRF) has been employed for this purpose by multiple generations of Mars rovers (i.e., Pathfinder, Spirit and Opportunity, Curiosity and Perseverance). The Planetary Instrument for X-ray Lithochemistry (PIXL) aboard Perseverance rasters a micro-focused X-ray beam to generate micron-mm-sized maps illustrating variations in elemental composition and allowing mission scientists to identify rock components (i.e., sedimentary grains, veins and igneous crystals). Energy-dispersive X-ray diffraction can also be detected with PIXL and can be used as an additional constraint on component boundaries, providing PIXL with the capability to map monocrystalline regions in-situ. Here we introduce and apply a new method where each diffraction peak is partitioned independently according to its energy, using the instrument geometry to inform consistent partitioning. Applying this method to datasets acquired from the Dourbes abrasion patch in the Séítah formation of Jezero crater, Mars, reveals monocrystalline regions that were hidden using previous methods. This application of the technique allows faster and more accurate visualization of petrographic textures in future PIXL datasets, in particular those with rock components that are not easily separable using stoichiometry alone.

¹Jean-Pierre Lorand,¹Sylvain Pont,¹Roger H. Hewins,¹Brigitte Zanda
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14233]
¹Institut de Minéralogie, Physique de la matière et Cosmochimie, et Muséum National d’Histoire Naturelle, UMR CNRS 7590, Sorbonne Université, Paris, France
Copyright Elsevier

Northwest Africa (NWA) 14672, the most highly shocked Martian meteorite so far, has experienced >50% melting, compatible with peak pressure >~65 Gpa, at a transition stage 6/7. Despite these extreme shock conditions, the meteorite still preserves a population of “large” Fe sulfide blebs from the pre-shock igneous assemblage. These primary blebs preserve characteristics of basaltic shergottites in term of modal abundance, preferential occurrence in interstitial pores along with late-crystallized phases (ilmenite, merrillite), and Ni-free pyrrhotite compositions. Primary sulfides underwent widespread shock-induced remelting, as indicated by perfect spherical morphologies when embedded in fine-grained silicate melt zones and a wealth of mineral/glass/vesicle inclusions. Extensive melting of Fe-sulfides is consistent with the decompression path experienced by NWA 14672 after the peak shock pressure at ~70 GPa. Primary sulfides acted as preferential sites for nucleation of vesicles of all sizes which helped sulfur degassing during decompression, leading to partial resorption of Fe-sulfide blebs and reequilibration of pyrrhotite metal/sulfur ratios (0.96–0.98) toward the low oxygen fugacity conditions indicated by Fe-Ti oxides hosted in fine-grained materials. The extreme shock intensity also provided suitable conditions for widespread in situ redistribution of igneous sulfur as micrometric globules concentrated in glassy portions of fine-grained lithologies. These globules exsolved early on quenching, allowing dendritic skeletal Fe-Ti oxide overgrowths to nucleate on sulfides.