4.5 Article

Mars Science Laboratory CheMin Data From the Glen Torridon Region and the Significance of Lake-Groundwater Interactions in Interpreting Mineralogy and Sedimentary History

Journal

JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
Volume 127, Issue 11, Pages -

Publisher

AMER GEOPHYSICAL UNION
DOI: 10.1029/2021JE007099

Keywords

Glen Torridon mineralogy; lacustrine groundwater mixing; Gale crater sedimentary history

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The Glen Torridon region in Gale crater on Mars exhibits strong clay mineral signatures, which have been confirmed by the CheMin instrument onboard the Curiosity rover. The presence of new phases such as Fe-carbonates and a novel peak at 9.2 angstroms suggests the potential existence of new mineral species on Mars. Co-occurrence of Fe-carbonate and Fe-rich clay minerals supports a conceptual model of a lacustrine groundwater mixing environment in the GT region.
The Glen Torridon (GT) region in Gale crater, Mars is a region with strong clay mineral signatures inferred from orbital spectroscopy. The CheMin X-ray diffraction (XRD) instrument onboard the Mars Science Laboratory rover, Curiosity, measured some of the highest clay mineral abundances to date within GT, complementing the orbital detections. GT may also be unique because in the XRD patterns of some samples, CheMin identified new phases, including: (a) Fe-carbonates, and (b) a phase with a novel peak at 9.2 angstrom. Fe-carbonates have been previously suggested from other instruments onboard, but this is the first definitive reporting by CheMin of Fe-carbonate. This new phase with a 9.2 angstrom reflection has never been observed in Gale crater and may be a new mineral for Mars, but discrete identification still remains enigmatic because no single phase on Earth is able to account for all of the GT mineralogical, geochemical, and sedimentological constraints. Here, we modeled XRD profiles and propose an interstratified clay mineral, specifically greenalite-minnesotaite, as a reasonable candidate. The coexistence of Fe-carbonate and Fe-rich clay minerals in the GT samples supports a conceptual model of a lacustrine groundwater mixing environment. Groundwater interaction with percolating lake waters in the sediments is common in terrestrial lacustrine settings, and the diffusion of two distinct water bodies within the subsurface can create a geochemical gradient and unique mineral front in the sediments. Ultimately, the proximity to this mixing zone may have controlled the secondary minerals preserved in sedimentary rocks exposed in GT.

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