Carbonate dissolution and replacement by odinite and saponite in the Lafayette nakhlite: Part of the CO2-CH4 cycle on Mars?

New mineralogical studies of Lafayette reveal that it contains a notably variable abundance martian carbonate. Four percent was identified in mesostasis (3.2%) and olivine-hosted (0.8%) fractures one polished section, but only 0.2% both textural types another. The carbonates are Mg0.0-2.0Cc13.2-38.6Sd17.7-81.9Rh3.1-42.9. They have undergone extensive amounts dissolution replacement as the nakhlite secondary fluid evolved, associated with precipitation ferric saponite olivine serpentine-like phyllosilicate mesostasis. carbonate has highest degree corrosion replacement. TEM analysis shown presence Fe-(hydr)oxide (likely ferrihydrite) nanoparticles on which can be linked to cessation more at those sites. mineral been described here basis WDS EDX analyses, HRTEM Fe-K XANES, odinite, ferric, 0.7 nm d001-spacings characteristic 1:1 structure. stage then formation occurred under circumneutral-alkaline conditions (7) < pH 10. This range is also where general mechanism switched from proton-promoted, water hydrolysis reaction reduction rates. As rates were reduced had cooled ≤50 °C, temperatures ∼25 dominated over dissolution. such crustal across upper crust, producing bicarbonate carbon dioxide, coupled phyllosilicates, would lead CH4 substantial via Fischer-Tropsch type reaction. results our study illustrate process explain relatively low detected Mars likely source for some methane Mars.