44-1 Cryo-Precipitation of Multi-Cation Brine Key to Understanding Sulfate Distribution in Gale Crater, Mars

Session: Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe, Part II

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From the first recording of sulfur abundances in the Martian soil by the Viking landers, sulfate salts have been identified extensively on Mars and most recently in Jezero crater by the Perseverance rover. The Chemistry and Mineralogy (CheMin) X-ray diffraction instrument and the Sample Analysis at Mars Evolved Gas Analyzer (SAM-EGA) onboard the Mars Science Laboratory Curiosity Rover have identified both crystalline and X-ray amorphous sulfates across the traverse, suggesting a complex sulfate story in Gale crater. In situ confirmation of the orbitally determined geological stratigraphy of Mg-sulfate-rich layer (sulfate unit) overlaying a phyllosilicate-rich layer by the Curiosity rover in Gale is hypothesized to reflect an environmental transition from a warm and wet Noachian era to a dry, acidic, and cold Hesperian era. However, recent studies show a more complex distribution of hydrous minerals on Mars including Noachian sulfates, late Amazonian clays, and late Hesperian clay-sulfate abundance ratios that indicate that sulfate compositions in Gale were formed and transformed by diverse local alteration environments. Similarly, the occurrence of multi-cation sulfates (amorphous and not detected by CheMin) has been confirmed by SO₂ evolution abundances detected from the mass spectral data collected by SAM.

Synthetic multi-cation (Fe, Mg, and Ca) brines were subjected to cryo-precipitation using and analyzed using a Labsys-EVO SAM-EGA analog instrument. Samples evolved SO₂ at characteristic temperatures comparable to drill samples analyzed across Gale crater and show that the presence of certain salts such as, Fe(III)-sulfates inhibit the formation of crystalline Mg-sulfates but not Ca-sulfates. Therefore, we hypothesize that the observed sulfate salts in Gale are likely products of interactions between late-stage diagenetic fluids and surface minerals under cryogenic conditions and are influenced by Fe-redox distribution. Our results indicate that Mg-Fe amorphous sulfates may have formed below the Mg-sulfate unit due to presence of excess Fe(III) in solution. In contrast, crystalline Mg-sulfates and siderite were able to precipitate in the sulfate unit which supports an Fe(II)-rich formation environment.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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