1. Introduction: The Spirit rover observed clastic rocks on Husband Hill and at Home Plate in the Columbia Hills of Gusev Crater. The rover’s APXS found these rocks to be nominally basaltic in overall composition and it’s Mini-TES instrument determined them to be rich in glasses. Basaltic glass can be produced from volcanism or as a result of impacts into a basaltic substrate. However, the basaltic glass resulting from both formation mechanisms appears similar to existing rover-based instrumentation. Basaltic glass can alter through weathering at ambient conditions, in a form of pedogenesis, producing disaggregated materials containing ferrihydrite, allophane, and kaolinite. Alteration through hydrothermal conditions or through emplacement of basaltic ash with steam leads to alteration through palagonitization. Palagonitized materials are well- cemented and the basaltic glass grains alter to palagonite and ultimately to smectites and zeolites (Schiffman et al., 2000 and 2002). In this investigation, we are examining fresh and altered basaltic glasses, and other granular materials, produced by a number of hydrovolcanic eruptions and also basaltic impact ejecta from Lonar Crater, India. We are using instrumentation analogous to that on-board the Mars Exploration Rovers and to some of Curiosity’s instruments to search for markers that may be distinctive of the formation process. We also seek to better understand the alteration processes of these materials and whether materials altered through pedogenesis or palagonitization. Our work has focused primarily on the characterization of fresh and altered tephra from hydrovolcanic field sites in Idaho, New Mexico, Utah and the characterization of Lonar Crater impact melts. P EDOGENIC VERSUS P ALAGONITIC A LTERATION OF H YDROVOLCANIC B ASALTIC G LASSES : C HARACTERIZATION THROUGH V ISIBLE -T HERMAL I NFRARED S PECTROSCOPY AND X-R AY D IFFRACTION A NALYSES : R ELEVANCE FOR E ARTH AND M ARS W.H. Farrand 1, S.P. Wright 2, T.D. Glotch 3, 1. Space Science Institute, Boulder, CO; farrand@spacescience.org 2. Auburn University, Auburn, AL 3. Stony Brook University, Stony Brook, NYfarrand@spacescience.org Acknowledgements: This work was funded through the NASA Mars Fundamental Research Program. B A B (c) A B C Fig. 1. Google Earth views of Idaho field sites. A. N. Menan Butte B. Sinker Butte C. White Butte D. Split Butte E. Pavant Butte F. Zuni Salt Lake Field Sites VNIR Reflectance Spectroscopy Fig. 4a. Reflectance spectra of hydrovolcanic basaltic glassy tephras from N. Menan Butte in progressive stages of alteration. TIR Emission Spectroscopy Fig. 5a. Emissivity spectra of hydrovolcanic basaltic glassy tephras from N. Menan Butte in progressive stages of alteration. See Table 1 for results of linear deconvolutions (Ramsey and Christensen, 1998) of these spectra. Mineral GroupNMB12-13NMB12-12NMB12-05NMB12-07 Feldspar0.001.009.020.00 CPX4.890.000.769.41 OPX0.00 0.76 Olivine0.00 1.879.09 Phyllosilicates44.7567.8754.0259.11 Glass38.6914.5610.800.00 Serpentine8.289.092.6716.59 Zeolites0.006.9311.970.00 Carbonates1.480.000.754.03 Silica0.000.562.460.00 Table 1. Blackbody normalized linear deconvolution results of spectra shown in Fig. 5. Mössbauer Spectroscopy Fig. 6. Mössbauer spectra of palagonite tuff, WhB12-03 and gray tuff WhB12-05. Micro-FTIR Analysis Select samples were analyzed using the FTIR microscope at the Vibrational Spectroscopy Lab at Stony Brook University. This analysis provided a means of identifying component materials in the tephra and impact ejecta products. Glassy basaltic tephra can alter through the process of palagonitization (Stroncik and Schmincke, 2002) or through pedogenic processes (Schiffman et al., 2000). Palagonitic alteration predominates in the tephra beds surrounding tuff rings and tuff cones. Unaltered sideromelane tuffs have low albedo reflectance spectra with broad Fe 2+ glass bands and no hydration bands. With increasing alteration, the tuffs take on a gray or brown appearance, with increasing development of hydration features. Highly palagonitized tuffs have an orange color, Fe 3+ absorption features, deep 1.4 and 1.9  m water bands and often a weak band at ~ 2.3  m indicative of smectites (Farrand and Singer, 1992) (Fig. 4). Fig. 4b. Reflectance spectra of Lonar crater altered ejecta and unaltered impact melt. Emissivity spectra of glass-rich samples display an asymmetric absorption band with a minimum at 9.5  m. With increasing alteration, and development of poorly crystalline smectites, the band appears more symmetric with a band minimum at 9.7  m. Highly palagonitized tuffs also contain carbonates, evinced in emissivity spectra by a 11  m band. Emissivity spectra of glass-rich hydrovolcanic tephras and Lonar crater impact melt appear highly similar (Fig. 5b). Fig. 5b. Emissivity spectra of glassy N. Menan Butte tephras and Lonar class 5b impact melt (Wright et al., 2011). Fig. 7. A. NMB12-01 sideromelane tuff composite of bands centered at 1230, 950, and 725 cm -1. Glass grains are cyan-colored. B. NMB12-03 palagonite tuff composite of same bands. Glass grains are cyan-colored, light green = smectites, dark green = palagonite, magenta = voids or carbonate veins. Mössbauer spectroscopy details the oxidation of Fe in the tephra and impact ejecta from Fe 2+ in glass to Fe 3+, largely in nanophase ferric oxides. Fig. 8. A. Plane polarized light view of a glass grain with a palagonite rind in Sinker Butte sample SB12N-03. B. Composite of micro-FTIR bands (same combination as above) with blue box over glass grain and red box over palagonite rind. C. Micro-FTIR spectra converted from reflectance to emissivity and wavelength space of glass and palagonite spectra. TIR spectra of pure palagonite at this scale have previously been unmeasured. Fig. 9. Spectra of micro- FTIR thin sections of Sinker Butte glass grain (black) and Lonar crater impact melt glass (blue). Discussion: Our analysis to date indicates that basaltic glass, be it produced via volcanic activity or through impact melting, has similar VNIR reflectance and TIR emission spectra. However, associated materials and alteration products could provide insights into the mechanism of formation and alteration. Work remains to be done to compare altered impact melts with basaltic glasses altered through palagonitization and through pedogenesis. Our work to date also highlights difficulties in determining the detailed mineralogy of clastic basaltic materials through both reflectance and emission measurements. The fractions of component materials derived through linear deconvolution shown in Table 1 indicates the presence of phyllosilicate minerals even in minimally altered basaltic tuffs where reflectance measurements, thin section analysis, and XRD studies (on-going at the time of this conference) indicate only glass and fragmental mineral clasts. This problem stems from the spectral similarity of clays, glasses, and some other high silica materials in the TIR- a problem that is still relevant to the determination of the TES “surface type 2” material covering much of the northern plains of Mars (Bandfield et al., 2000). References: Bandfield, J.L. et al. (2000) Science, 287, 1626-1630; Farrand, W.H. and R.B. Singer (1992) JGR, 97, 17,393-17,408; Ramsey, M.S. and P.R. Christensen (1998) JGR, 103, 577-596; Schiffman, P., et al. (2000) Geochem., Geophys., Geosyst., 1, 2000GC000068; Stroncik, N.A. and H-U. Schmincke (2001) Geochem., Geophys., Geosyst., 2, 2000GC000102; Wright, S.P. et al. (2011) JGR, 116, 10.1029/2010JE003785. Fig. 2. A. Google Earth view of Lonar Crater. B. Impact melt clast. Fig. 3. A. Tuff beds at Split Butte. B. Tuff beds a N. Menan Butte. X-Ray Diffraction: XRD studies of samples are on-going. Preliminary results in Table 2 indicate smectite in both the altered hydrovolcanic tephra and in altered Lonar Crater impact melt. While smectite was expected in the N. Menan Butte tuffs due to the palagonitization alteration path-way common in tuff cones, its presence in the Lonar Crater samples indicates a possible hydrothermal alteration rather than ambient pedogenic alteration. SamplesMaterialXRD-determined minerals NMB12-03N. Menan Butte palagonite tuffSmectite, calcite, phillipsite NMB12-07N. Menan Butte palagonite tuffSmectite, calcite, phillipsite LC-LLG-135Lonar Crater altered impact meltSmectite, calcite LC06-198Lonar Crater impact meltNo alteration products LC09-235 (1)Lonar Crater altered impact meltSmectite, quartz, albite LC09-235 (2)Lonar Crater altered impact meltSmectite, calcite Table 2. XRD results of N. Menan Butte tuffs and Lonar Crater impact melts