EPSC Abstracts Vol. 13, EPSC-DPS2019-1258-1, 2019 EPSC-DPS Joint Meeting 2019 c Author(s) 2019. CC Attribution 4.0 license. Characterizing Environments Containing Complex Phyllosilicate-Sulfate Assemblages as Analogs for Mars Janice L. Bishop (1), Jessica Flahaut (2), Selena L. Perrin (1), (1) SETI Institute, Mountain View, CA, USA ([email protected]), (2) CRPG-CNRS, Vandœuvre-lès-Nancy, France. Abstract of gypsum has a stronger band at 2.22 µm and a weaker band at 2.26 µm, while jarosite has a stronger Complex phyllosilicate/sulfate assemblages have band at 2.26 µm with a shoulder at 2.22 µm (Fig. 1b). been identified through a spectral “doublet” feature The mixture exhibits a doublet with a stronger band near 2.21-2.23 and 2.26-2.28 µm in orbital CRISM at 2.26 µm but a clearly distinguishable band at 2.22 spectra at multiple locations on Mars including µm. This is very similar to bands observed in the Mawrth Vallis [1], Noctis Labyrinthus [2], Melas “Orange soil” spectrum (Fig. 1b) for ~52% jarosite, Chasma [3], and Ius Chasma [4]. In this study we ~26% gypsum and ~21% quartz by XRD. explore analog sites featuring mixtures of jarosite, gypsum, phyllosilicates, and opal that exhibit spectral “doublet” features related to this unique martian signature. We focus here on evaporite samples from shallow salt ponds at Chilean salars [5], pedogenic samples altered by acidic waters at the Painted Desert [6], and altered ash near fumarole vents [7,8]. 1. Introduction Samples were collected from multiple field sites in order to gain an understanding of the spectral properties of complex phyllosilicate-sulfate assembl- ages in a variety of geochemical environments. When possible, we brought visible/near-infrared (VNIR), XRD, and Raman instruments to the field for in situ investigation of these sites. Samples were also characterized in the lab in more detail. VNIR spectra were measured using an ASD FieldSpecPro from 0.35-2.5 µm for comparison with CRISM spectra. 2. Painted Desert Sulfate Hill Figure 1: a) View of jarosite outcrop at Sulfate Hill The Painted Desert includes wide expanses of in the Painted Desert. Gypsum crystals are found in a alternating phyllosilicate- and iron oxide-bearing thin white layer here ~3 cm below the surface (image units, likely formed in a pedogenic environment. The ~40 cm wide). b) VNIR spectra of the orange soil Sulfate Hill site contains outcrops of jarosite and from a), gypsum, jarosite, and a mineral mixture. gypsum [6] that may have formed through acidic Spectral features marked by lines. groundwaters. These samples exhibit a spectral doublet (Fig. 1) similar to that observed for some 3. Chilean Salars regions of Mars. OH combination bands are present at 2.22 and 2.26 µm in spectra of both gypsum and Samples were investigated from shallow salt ponds at jarosite, but these bands have different relative the Antofagasta region of Chile, north of the intensities in spectra of each mineral. The spectrum Atacama region [5] containing gypsum, other sulfates, halite, phyllosilicates, and opal. Spectra of many of these samples contain “doublet” features near 2.22 and 2.26 µm related to gypsum (Fig. 2). Other studies of shallow salt ponds in Western Australia have observed similar minerals [e.g. 9]. Figure 3: a) View of alteration above a fumerole vent at Campi Flegrei caldera. b) VNIR spectra of two jarosite-bearing field sites. Figure 2: a) View of salt ponds at Antofagasta region. b) VNIR spectra of gypsum-bearing samples References compared with gypsum. [1] Bishop J. L. et al. (2013) What the ancient phyllosilic- ates at Mawrth Vallis can tell us about possible habitability 4. La Solfatara Campi Flegrei on early Mars. Planet. Space Science, 86, 130-149. [2] Weitz C.M. et al., (2011) Diverse mineralogies in two The Campi Flegrei caldera at La Solfatara volcano troughs of Noctis Labyrinthus, Mars. Geology, 39, 899-902. near Naples, Italy contains active fumarole vents that [3] Weitz C.M., Noe Dobrea E. & Wray J.J. (2015) are altering the ash to form mixtures of phyllo- Mixtures of clays and sulfates within deposits in western silicates, opal, jarosite, and other sulfates that exhibit Melas Chasma, Mars. Icarus, 251, 291-314. spectral doublet signatures (Fig. 3) [8]. Another study of altered ash near vents at Kilauea caldera, HI [4] Roach L.H. et al. (2010) Hydrated mineral stratigraphy contains jarosite, gypsum, phyllosilicates, and opal of Ius Chasma, Valles Marineris. Icarus, 206, 253-268. and also exhibits similar spectral doublets [7]. [5] Flahaut J. et al. (2017) Remote sensing and in situ mineralogic survey of the Chilean salars: An analog to 5. Implications from Analogs Mars evaporate deposits? Icarus, 282, 152-173. The spectral doublet observed on Mars could be due [6] Perrin S. L. et al. (2019) Analysis of unique martian sulfate outcrops based on samples from the Painted Desert to phyllosilicate-sulfate mixtures formed in a variety th of acidic and salty environments. Assemblages Sulfate Hill analog site and lab mixtures. 49 LPSC, #1903. containing gypsum and opal are characteristic of [7] Bishop J.L. et al. (2015) Solfataric alteration at Hawaii evaporitic salars, while jarosite is often observed near as a potential analog for Martian surface processes. AGU fumaroles, and jarosite/gypsum mixtures could fall meeting, Abs. #62066. represent hydrothermal settings including acidic [8] Flahaut J. et al. (2019) The Italian Solfatara as an groundwater or fumarole vents. analog for Mars fumarolic alteration. American Mineralogist, in review. Acknowledgements [9] Benison K.C. & Bowen B.B. (2006) Acid saline lake We are grateful to support from the NASA systems give clues about past environments and the search Astrobiology Institute. for life on Mars. Icarus, 183, 225-229. .