Evaporative evolution of Martian brines based on halogens in nakhlites and MER samples
- Lockheed
Comparison of Cl and Br from Nakhla viens to MER samples suggests two kinds of brine solutions existed on Mars, one early and one late in the evaporation sequence. These solutions precipitated the secondary salts at the Meridiani and Gusev sites. We have recently reported the Cl and Br abundances determined by APS X-ray Microprobe and EMPA analyses of secondary aqueous minerals in Nakhla veins and discussed the significance of Cl-Br correlations with respect to the evolution of brine solutions on Mars. In that study, we suggested that the low Br concentration ({approx}10 ppm) in Lafayette Iddingsite is indicative of early stage of evaporation during progressive evolution of Martian brine solutions, which is, in turn, consistent with the petrographic evidence of early deposition of salt sequence of carbonate-sulfate- and no halite in Lafayette. We showed that the high Br concentrations of {approx}240 ppm in secondary salts in Nakhla veins similarly indicate late stages of evaporation in evolving Martian brine solutions which is again consistent with petrographic evidence of late stage deposition of salt sequence i.e. carbonate-sulfate-halite in Nakhla. When sea water evaporates under equilibrium conditions, the most insoluble carbonates (siderite and calcite) deposit first, followed by sulfates (gypsum and anhydrite) and finally the water-soluble halides are precipitated when the water content is sufficiently low. In the present study, we make a detailed comparison of Cl/Br ratios in secondary minerals in nakhlites with those in MER soils and rocks at Gusev and Meridiani and show that the compositions of solutions that inundated Lafayette iddingsite (early stage) and Nakhla veins (late stage) include the range of solution-compositions that gave rise to a variety of secondary salts at Gusev and Meridiani sites. Further, the results obtained here suggest that two kinds of brine solutions (one, late and the other, early or intermediate stage) seem to have inundated most of the rocks and soils to varying degrees and precipitated the secondary salts at Meridiani and Gusev sites.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1008946
- Resource Relation:
- Conference: Lunar and Planetary Science XXXVI;March 14-18, 2005 ;League City, TX
- Country of Publication:
- United States
- Language:
- ENGLISH
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