¹Kierra Wilk,²Janice L. Bishop,³Catherine M. Weitz,⁴Mario Parente,⁴Arun M. Saranathan,^4,5Yuki Itoh,⁶Christoph Gross,⁷Jessica Flahaut,⁵Frank Seelos
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115800]
¹Brown University (Providence, RI)
²SETI Institute & NASA-Ames (Mountain View, CA)
³Planetary Science Institute (Tucson, AZ)
⁴University of Massachusetts at Amherst (Amherst, MA)
⁵Johns Hopkins University Applied Physics Lab (Laurel, MD)
⁶Free University of Berlin (Berlin, Germany)
⁷CRPG, CNRS/Université de Lorraine (Vandœuvre-lès-Nancy, France)
Copyright Elsevier

Intriguing outcrops in Ius Chasma provide a window into past aqueous processes in Valles Marineris, Mars. Hydrous sulfate minerals are abundant throughout this region, but one area in Ius Chasma includes phyllosilicates, opal, and additional materials with unusual spectral features. This study at Geryon Montes, an east-west horst that divides Ius Chasma into a northern and southern canyon, exploits recent advances in image calibration and feature extraction techniques for analysis of hyperspectral images acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Specifically, a unique spectral “doublet” feature with absorptions at 2.21–2.23 and 2.26–2.28 μm is isolated at the border of phyllosilicate-bearing and sulfate-bearing regions in Ius Chasma and surveyed to characterize outcrops that may represent a changing climate on Mars. We document and map three distinct forms of this “doublet” material in relation to phyllosilicates and opal. Analyses of compositional maps derived from CRISM overlain on High Resolution Stereo Camera (HRSC) and High Resolution Imaging Science Experiment (HiRISE) imagery has revealed the presence of these hydrated outcrops along the wall rocks below a breach in the Geryon Montes, bordering a canyon containing abundant hydrated sulfates. Our investigation supports formation of these unique alteration phases through acid alteration of ancient smectites in the wall rock as the sulfate brine overflowed the south canyon of Ius Chasma at the breach in Geryon Montes and penetrated the deeper northern canyon.

¹Shaofan Che,¹Kenneth J. Domanik,¹Yao-Jen Chang,^1,2Thomas J. Zega
Earth and Planetary Science Letters 621, 118374 Link to Article [https://doi.org/10.1016/j.epsl.2023.118374]
¹Lunar and Planetary Laboratory, University of Arizona, Tucson AZ, United States of America
²Department of Materials Science and Engineering, University of Arizona, Tucson AZ, United States of America
Copyright Elsevier

The important role that aqueous fluids played during the evolution of carbonaceous chondrites (CCs) and the carbonaceous asteroids that they derive from is well documented. In comparison, our understanding of how such fluids affected ordinary chondrites (OCs) and their S-type asteroid parent bodies is less mature in part due to the intense thermal metamorphism that overprinted the records of alteration. Further, that only a small suite of unequilibrated OCs shows evidence of hydration hinders our understanding of the role that fluids played in the evolution of OCs and S-type asteroids. Here we report a microstructural analysis on halite (NaCl) and sphalerite (ZnS) in Sidi El Habib 001 (SEH 001), a H5 OC that provides new insights into the role of fluids on the OC parent bodies. Our data reveal that halite contains alteration relicts of submicron silicates, and that widespread sphalerite spatially correlates with halite. This relationship suggests that sphalerite formed from the same hydrothermal fluid that precipitated halite, consistent with experimental and theoretical work showing that Cl-rich fluids induce complexation of Zn and significantly enhance its mobility. We hypothesize that Cl-rich hydrothermal fluids resulted from melting of locally concentrated HCl hydrate, which produced acidic fluids capable of dissolving chondritic mineral phases. The pH of the fluid presumably varied on a micrometer scale due to different rates of hydrolysis reactions as a function of grain size, as illustrated by the absence of halite in SEH 001 chondrules. Such a fluid-alteration model is attractive because it offers a reasonable explanation for the limited and heterogeneous alteration effects in OCs.