Paper No. 236-1
Presentation Time: 8:05 AM
A HIGH CARBONATE ALKALINITY, LOW PH LAKE IN JEZERO CRATER, MARS (Invited Presentation)
HUROWITZ, Joel, Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, ALLWOOD, Abigail, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, CABLE, Morgan L., Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, CATLING, David, Earth & Space Sciences, University of Washington, Seattle, WA 9810, CLARK, Ben, Space Science Institute, Boulder, CO 80301, FISCHER, Woodward, Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, KIZOVSKI, Tanya, Department of Earth Sciences, Brock University, St. Catharines, ON ON L2S 3A1, Canada, SIEBACH, Kirsten, Geoscience, Rice University, Houston, TX 77005, TICE, Michael M., Geology and Geophysics, Texas A&M University, College Station, TX 77802 and TREIMAN, Allan, Lunar and Planetary Institute, Houston, TX 77058
The Mars 2020
Perseverance rover investigated sedimentary sandstones and conglomerates along the upper geomorphic surface of the western fan/delta in Jezero crater. Clastic grains include abundant olivine, and lesser clinopyroxene, plagioclase, mafic lithic clasts, and Cr-spinels. These detrital phases are accompanied by abundant Fe-Mg carbonate (present as mm-scale lithic clasts, grain coatings, fine-grained matrix, and cement), silica, Fe-Mg silicates with compositions approximating that of serpentine (greenalite-hisingerite-lizardite) and low-Al smectitic clay. Ca- and Fe-phosphates are also found in variable abundances, and Fe-Mg-Ca sulfates frequently cross-cut, or fill void space between, the previously described minerals. The Mg# of primary and secondary phases varies from ~40-60 and the presence of a variety of nominally Fe(II)-bearing mineral phases is consistent with anoxic conditions.
We will present the results of geochemical modeling that indicate that the reaction of ultramafic, olivine-dominated rock with meteoric fluid at variable W/R ratio, followed by evaporation, yields an assemblage of secondary mineral phases consistent with the suite of minerals observed by the instrument suite onboard the Perseverance rover. The meteoric fluid is anoxic, with high DIC resulting from a high pCO2 atmosphere and millimolar SO42- and Cl- from volcanic gas input. Low- to intermediate W/R ratio weathering and evaporation produces secondary phases that are most like those observed in carbonate-rich progradational topset and foreset sedimentary rocks. In contrast, the suite of minerals observed in sulfate-rich strata of delta front, which are finer-grained lacustrine sediments deposited from suspension and traction, require higher W/R ratio weathering followed by evaporation. Thus, fan/delta mineralogy is intimately linked to catchment hydrology.
Our geochemical models predict that the lake in Jezero crater was characterized by high carbonate alkalinity, dominated by HCO3-, and was driven by evaporation to moderately low pH, between 4-6, under all modeled conditions. Thus, while alkaline lakes on Earth are frequently associated with both high carbonate alkalinity and high pH, Martian lakes have a unique character of their own, where high carbonate alkalinity is accompanied by sub-neutral pH conditions.
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