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Acidic Weathering of Phyllosilicates

Acidic Weathering of Phyllosilicates. Travis Altheide * , Vincent Chevrier, and Patricia Gavin. Workshop on Martian Phyllosilicates CNES Paris, France Oct. 21 – 23, 2008. psp_001784, HiRISE. Mawrth Vallis, OMEGA. Layered deposits in outflow channels (Wray, et al. 2008; Bishop, et al. 2008)

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Acidic Weathering of Phyllosilicates

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  1. Acidic Weathering of Phyllosilicates Travis Altheide*, Vincent Chevrier, and Patricia Gavin Workshop on Martian Phyllosilicates CNES Paris, France Oct. 21 – 23, 2008 psp_001784, HiRISE Mawrth Vallis, OMEGA

  2. Layered deposits in outflow channels (Wray, et al. 2008; Bishop, et al. 2008) Fe,Mg-smectite: orange/red Fe2+ bearing phases: yellow/green Al-phyllosilicate and hydrated silica: blue Small deposits with phyllosilicates and sulfates mixed: Aram Chaos, Terra Meridiani, and Becquerel crater (Poulet et al., 2005) Silica deposits idendified in Gusev Crater (Squyres, et al., 2008) Mineralogical Context Bibring, et al. 2005

  3. Complex Aqueous History: phyllosilicates vs. sulfates • Different geochemical environments between phyllosilicates and sulfate deposits (Bibring et al., 2006; Chevrier et al., 2007) • But small deposits of phyllosilicates mixed with sulfates • Gusev Crater: no phyllosilicates, mostly sulfates and low pH minerals • Questions: what, if any, is the effect of acidic weathering on phyllosilicates? Is there a mineralogical relationship between the two?

  4. Materials and Protocol

  5. Analytical Methods Infrared Spectroscopy • 1.0 – 2.4 μm • X-ray Diffraction • Method described in abstract • ESEM – EDAX • Relative elemental analysis • Atomic Absorption • Quantify extent of Fe and Mg leaching

  6. FT-IR: nontronite

  7. FT-IR: montmorillonite

  8. FT-IR: kaolinite

  9. FT-IR: chlorite

  10. XRD: nontronite, pH 0 Control Sample Rho = rhomboclase Silica Rho Rho

  11. ESEM/EDAX: nontronite, pH 0 20 μm O = 45.86 Si = 40.31 Al = 2.52 S = 9.40 Ti = 1.90 O = 45.91 Si = 41.99 Al = 2.05 S = 8.08 Ti = 1.98

  12. XRD: montmorillonite, pH 0 Control Sample Mus/Kao Al-Si Kao = kaolinite Mus/Kao Mus = muscovite Al-Si = hydrated aluminum silicate

  13. ESEM/EDAX: montmorillonite, pH 0 O = 45.59 Si = 41.22 Al = 4.10 S = 7.71 Mg = 1.38 O = 48.63 Si = 40.19 Al = 4.38 S = 6.80 Mg = 0.00

  14. XRD: kaolinite, pH 0 Control Sample Kao Kao = kaolinite Kao Kao Si02

  15. ESEM/EDAX: kaolinite, pH 0 O = 47.03 Si = 34.36 Al = 15.05 S = 3.56 O = 44.86 Si = 34.92 Al = 15.35 S = 4.87

  16. Summary of Results: Solid Phase

  17. Stability of Mg-rich Phyllosilicates: pH and Si02

  18. Implications for Mars • Transition from nontronite to kaolinite indicates a “global” decrease in pH • Precipitation of phyllosilicates in increasing acidic conditions • Progressive leaching of Fe, Mg, Ca, Na ions from phyllosilicate due to acidic waters (pH < 6) • More compatible with formation of amorphous silica (hydrothermalism can also explain) • Association of sulfates plus hydrated silica resulting from acidic weathering of phyllosilicates?

  19. Continuing Work • Investigation of Fe2+ phases • Chlorite • Serpentine • Liquid phase characterization • Atomic absorption: Quantify Fe and Mg leaching • Thermodynamic and kinetic modeling (Chevrier, 2008: this session)

  20. Acidic Weathering of Phyllosilicates Travis Altheide*, Vincent Chevrier, and Patricia Gavin Workshop on Martian Phyllosilcates CNES Paris, France Oct. 21 – 23, 2008 Psp_001784, HiRISE Mawrth Vallis, OMEGA

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