Reactive Transport Modeling Of Aqueous Alteration In The Murray Formation, Gale Crater, Mars

Past aqueous conditions in the Murray formation at Gale crater, Mars contain important clues to interpret ancient environments, potential habitability, and the biosignature preservation potential of that planet. CheMin X-ray diffraction measurements of samples from the Murray formation indicate changes in mineralogy with stratigraphy that have been attributed to both changes in depositional environment and diagenetic alteration. In order to test the impact of multiple different conditions of diagenetic alteration on the mineral assemblage, we performed reactive transport modeling of liquid water interactions with parent materials. We varied pH and temperature in a two-layer model using the CheMin measured mineralogy of the Murray formation mudstone samples Buckskin, Telegraph Peak, Mojave2, and Confidence Hills in the Pahrump Hills locality. The two-layer model was developed with input pH ranging from 2 to 8 and temperature either constant (1 and 40 degrees C) or varied from 1 to 40 degrees C. Modeling results compared with CheMin measurements of primary minerals, amorphous silica, hematite, nontronite, jarosite, and fluorapatite indicate that the aqueous alteration within the Murray formation is consistent with diagenetic alteration under acidic (pH 2) input solutions and increasing temperature (1-40 degrees C) conditions with depth. These results indicate that the mineralogy and geochemistry of the Murray formation likely reflect an aqueous past that contained multiple fluids and variable conditions over both temporal and spatial scales, and can help interpret locations that could both be habitable and preserve past biosignatures.