Laboratory simulations of Mars evaporite geochemistry

Abstract

[1] Evaporite-rich sedimentary deposits on Mars were formed under chemical conditions quite different from those on the Earth. Their unique chemistries record the chemical and aqueous conditions under which they were formed and possibly subsequent conditions to which they were subjected. We have produced evaporite salt mineral suites in the laboratory under two simulated Martian atmospheres: (1) present-day and (2) a model of an ancient Martian atmosphere rich in volcanic gases. The composition of these synthetic Mars evaporites depends on the atmospheres under which they were desiccated as well as the chemistries of their precursor brines. In this report, we describe a Mars analog evaporite laboratory apparatus and the experimental methods we used to produce and analyze the evaporite mineral suites. The acidic, "paleo-Mars" gas mixture was CO 2 with trace amounts of SO 2 , N 2 O, and HCl to simulate an atmosphere influenced by volcanic emissions. Brines formed by the interaction of water with an SNC-derived synthetic Mars mineral mix were produced under the acidic Mars atmospheric gas mixture. The brines were then desiccated under the two different simulated Mars conditions in the evaporite apparatus. Infrared reflectance spectroscopy and SEM microprobe analyses reveal that salts precipitated from the brine evaporated under simulated present Mars conditions were chemically different from those formed under the acidic Mars atmosphere conditions. The primary salt precipitated from the brine evaporated under present-day Mars conditions was a hydrated calcium sulfate, with lesser amounts of a magnesium sulfate and aluminum sulfate. Salts precipitated from the brine evaporated under an acidic atmosphere were dominated by magnesium sulfates, with lesser amounts of Na 2 SO 4 . These experiments suggest ways that relative cation abundances in Martian sulfate-bearing sediments can indicate the atmospheric and aqueous conditions under which they were formed. We conclude that the salts that make up the Meridiani sediments were probably formed by the interaction of water and igneous rocks at a high water-to-rock ratio, followed by desiccation under an atmosphere rich in acidic volcanic volatiles. The formation of Ca sulfates on Mars has most likely been due to the evaporation or freezing and sublimation of waters in equilibrium with an atmosphere much like the present.

Columbus crater and other possible groundwater-fed paleolakes of Terra Sirenum, Mars

“…As the CRISM global mapping data set nears completion, broader searches for evaporites in paleolakes will be possible. Exploring the range of evaporites in Martian paleolakes could reveal not only how lake chemistry varied in space and time, but it may also constrain the composition of the ancient Martian atmosphere [e.g., Moore et al , 2010; Wray et al , 2009c].…”

Thermal infrared and Raman microspectroscopy of moganite-bearing rocks

“…Although moganite has not yet been identified on Mars, its formation is dependent upon the presence of iron in the fluid as well as high activity of alkalis and/or sulfates (Heaney and Post 1992;Heaney 1995;McLaren and Pitkethly 1982). In addition Al 3+ can act as a catalyst in the formation of agate incorporating moganite (Story et al 2010;Moore et al 2010;Wang and Merino 1990). In situ and orbital observations have provided widespread evidence for the presence of iron-rich fluids in diagenetic and hydrothermal environments (Ming et al 2008) through detections of Fe-bearing sulfates (Squyres et al 2004;Wray et al 2011) and phyllosilicates (Poulet et al 2005;Bibring et al 2006); Al-phyllosilicates are less common but still present (Noe Dobrea et al 2010).…”

The Role of Terrestrial Analogs in the Exploration of the Habitability of Martian Evaporitic Environments

“…Martian salts, however, were presumably formed under different chemical conditions compared to the Earth, with aqueous alteration possibly related to high temperature and, as a consequence, differences in the ionic balance. For explaining the origin of mobile ions in the Martian regolith, Moore et al ( 2010 ) suggested that the following possible explanations should be considered: alteration of basalts by hot hydrothermal fl uids, precipitation of volcanic-derived aerosol/gas compounds, groundwater/ igneous rock interactions, and, lastly, the falling of meteorites. Experiments on evaporite salts in simulated modern and ancient Martian conditions (e.g., Bullock On Earth, as well as on Mars, hydrous Mg sulfates abound in marine and continental evaporite environments.…”