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Project Progress

Saline Lakes and Gypsum Dunes in the Rio Grande Rift System as Analogues for Sulfate Deposits on Mars

Sulfates appear to be a significant part of rocks and regolith exposed at or near the surface of Mars. We are pursuing, therefore, a latitudinal study of Salt Basins developed along the Rio Grande Rift as a terrestrial analog to sulfate deposition in the past on Mars. The following processes are being addressed: 1) local and regional influences of volcanism on sulfur cycle, 2) formation and biogeochemical transformation of sulfate-rich deposits in playas systems and domes from closed-drainage basins, and 3) evolution of gypsum eolian systems in regional scale. Geochemical (major elements) and stable isotopic (³⁴S/³²S, ¹⁸O/¹⁶O, ²H/¹H) compositions of water and sediment samples are combined with geomorphic analysis of aerial photographs to gain quantitative and qualitative insights into processes influencing production and preservation of gypsum in saline basins along the Rio Grande Rift system.

Geochemical analyses were coupled with seasonal field observations at the Estancia Basin, White Sands National Monument, Guadalupe Mountains National Park and Cuatro Ciénegas Basin. Based on sample collection in January, May, August, October of 2007 and April of 2008, we have reached a few general conclusions. Sulfate deposits in modern playas, paleo-lakes and gypsum dunes from the Rio Grande rift system are sourced primarily from underlying Permian evaporates during dissolution by meteoric waters with only minor contributions from oxidation of ascending hydrothermal fluids. Surprisingly, isotopic signatures related to microbial sulfate reduction are not evident in most of the studied lake and dune deposits from the Rio Grande rift. By extension to Mars, it appears that gypsum dunes in the Olympia-Undae region on Mars could be sourced from confined groundwater or surface water episodically released during melting of the Martian polar ice cap.

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