LASER RAMAN SPECTROSCOPIC MINERAL IDENTIFICATIONS OF ACCIDENTAL DAUGHTER CRYSTALS IN BEDDED HALITE: IMPLICATIONS FOR REFINING PARENT WATER CHEMISTRY ON EARTH AND MARS

Micron-scale crystals in primary fluid inclusions within halite gives clues about the geochemistry of past saline waters. Here, we describe petrographic, microthermometric, and Raman spectral observations of crystals in bottom-growth and cumulate halite crystals from Mars-analog acid and neutral salt lakes, and we make interpretations about past lake water chemistry. Samples include modern lake halite from Western Australia and ancient lake halite from Proterozoic Browne Formation of central Australia, the Permian Opeche Shale of North Dakota, and the Permian Nippewalla Group of Kansas. Our results show that: (1) entrapped crystals are situated within primary fluid inclusions and as solid inclusions along growth bands in host halite; (2) daughter crystals in fluid inclusions do not change upon heating or cooling on a fluid inclusion stage; (3) a variety of sulfate minerals exist, including Ca-sulfates, acid hydrated sulfates, and unidentified hydrated sulfates; and (4) rare carbonate grains coated with hematite were observed in some inclusions. We propose that most accidental daughter crystals co-precipitated with halite in sulfate-rich, metal-rich, complex acid lake waters. Grains transported into lakes by winds and/or floods are also represented. Similar petrographic and chemical analyses of Mars Sample Return salts may refine understanding of past martian water composition and habitability.