Chlorine/bromine ratios in fracture-filling aqueous alteration products in Nakhla olivine
- Max-Plank Inst
The Cl/Br ratios in fracture-filling materials in veins in Nakhla olivine was determined using x-ray microprobe (Br) and EDX (Cl) techniques. The Cl/Br ratio of 55 +/- 13 shows that the secondary altered material is pristine, extraterrestrial and akin to the Martian soil. During the early Martian history, volcanic emanations contributed large excesses of volatiles including halogens, sulfur and water to the Martian crust. These chemically-reactive elements had undergone extensive redistribution over time due to a variety of surface processes on Mars. To understand the nature of the alterations due to aqueous activity in the Martian surface environment, a study of halogens, in particular Cl/Br ratios in secondary mineralization products may provide valuable insights. Dreibus and Waenke arrived at a Cl/Br ratio of {approx}110 for the Martian surface materials by studying glasses and bulk samples of several SNC meteorites using neutron activation. Nakhla probably offers the most diverse suite of aqueous precipitates to be found among the SNC meteorites. Numerous veins of hydrous clay within olivine grains are present in Nakhla. Bridges and Grady and Wentworth and McKay observed massive concentrations of halite of probable Martian evaporitic origin, in association with siderite and anhydrite in interstitial areas in Nakhla. Dreibus et al. reported Cl/Br ratios in 3 Nakhla fragments from 104 to 550 and found that 90% of the Cl and Br was readily leachable from this material. Their Nakhla leachate ratio was 580. Their analysis of an attached salt grain yielded a ratio of 5440, similar to that in table salt. Xirouchakis et al. found 20 ppm Br in glass veins in Los Angeles shergottite based on XRF measurements with the x-ray microprobe (beamline X26A) at the Brookhaven Nat. Lab. We examine in this study whether a Cl/Br ratio similar to that of Dreibus and Waenke is also present in products of secondary mineralization, generated as a result of aqueous alteration in some SNC meteorites. We have studied the Cl/Br ratios in fracture-filling materials in veins in Nakhla olivines (thin sections) by determining Br contents using the X-ray Microprobe facility at GeoSoilEnviroCARS (Advanced Photon Source/University of Chicago) and by determining Cl using SEM-based EDX measurements at the same sites in the veins.
- Research Organization:
- Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1008874
- Country of Publication:
- United States
- Language:
- ENGLISH
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