New hydrated spectral phase and stratigraphy of smectites

New hydrated spectral phase and stratigraphy of smectites, sulfates, and other hydrated minerals in Ius Chasma, Valles Marineris L Roach, JF Mustard, S Murchie, RE Milliken, K. Litchenberg, BL Ehlmann, J Bishop, RE Arvidson, and the CRISM Team Martian Phyllosilicates: Recorders of Aqueous Processes Oct 21, 2008

• Hydrated silica stratigraphy • Sulfate stratigraphy • Nontronite and doublet stratigraphy • Identification of doublet mineralogy • Role of Landslides and Faulting

• Hydrated silica stratigraphy • Sulfate stratigraphy • Nontronite and doublet stratigraphy • Identification of doublet mineralogy • Role of Landslides and Faulting

Hydrated silica in multiple fine layers in wallrock at head of Louros Valles and at base. Formed on plateau and washed into trough. Restricted to region near sapping channels. Louros Valles headwall Tyrrhena Mouth Headwall Opal (library) FRT 00009998 Louros Valles mouth HRS 0000 B 8 EB

• Hydrated silica stratigraphy • Sulfate stratigraphy • Nontronite and doublet stratigraphy • Identification of doublet mineralogy • Role of Landslides and Faulting

Sulfates Elevation Contour -4200 m -3500 m Kieserite PHS Doublet Sulfates are within enclosed topographic lows – suggest they were formed by evaporation of a closed basin. First polyhydrated sulfate (PHS), then kieserite as the brine concentrated. Based on shot data, kieserite found below -4175 m, with PHS and doublet at higher elevations (-3700 to -4175 m)

FRT 00008950 and PSP_005940_1710 Hydrated silica 150 m Sulfate Hydrated silica found overlying PHS, probably sourced from sapping channel Hydrated silica layer < few m thick Thin layer of loose, non-hydrated dark material only partially fills cracks (arrow)

Sulfate and hydrated silica

2 1 • Hydrated silica stratigraphy • Sulfate stratigraphy • Nontronite and doublet stratigraphy • Identification of doublet mineralogy • Role of Landslides and Faulting

Layered Smectite clays Nontronite in thin layers overlain by doublet material. In one case doublet unconformably drapes nontronite. Polygonally fractured but no layering or relief exposed. Nontronite-bearing unit Doublet material-bearing unit Kieserite PHS Doublet 500 m across 180 m across

Hi. RISEPSP_006718 colorized with FRT 000085 A 4 (RGB: 2. 5, 1. 08 μm)

Layered Smectite clays Doublet unit is brighter, more fractured, and clearly overlies smectite (smoother layered material). Window into layered smectite through doublet material Doublet unit drapes previously eroded smectite layered unit

Layered Smectite clays Nontronite (green) and doublet (blue) FRTBFE 4 FRT 9 B 27 FRTA 202 FRT 823 A

FRT 00009 B 27, looking S Nontronite (green) at higher elevation than doublet. Adjacent obs shows doublet material overlying nontronite.

Doublet spectral type Some variability in relative strength of 2. 21 and 2. 27 um bands

Doublet spectral type No library spectra are perfect matches

• Hydrated silica stratigraphy • Sulfate stratigraphy • Nontronite and doublet stratigraphy • Identification of doublet mineralogy • Role of Landslides and Faulting

Landslides of hydrated material Next slide Smectite and Doublet Multiple landslide events range from “dry” (leftmost, with no mineral signatures) to “wet” (rightmost) and nontronite and doublet material in breccia. Central landslide is not yet determined. Landslides similarly fluidized. Leftmost landslide material overruns doublet breccia material, possibly from earlier landslide Nontronite and doublet material not localized to specific breccia blocks

Landslides of hydrated material Doublet-only material: located in older landslides or in basement breccia? FRT 905 B FRT 27 E 2 Distinctive variegated color Hi. RISE next page FRTA 396

Landslides of hydrated material PSP_006652_1725, overlapping FRTA 396 Folds, fractures, and megabreccia blocks. All with 1. 4, 1. 9, 2. 22, and 2. 27 μm abs. Images ~250 m across

Interpreted Ius Chasma Stratigraphy – Sulfates form by closed evaporating basin without recharge – Smectite in both breccia and matrix of landslides – Noachian megabreccia altered by hydrothermal processes? Could non-hydrated mineral-bearing landslides be unaltered Hesperian material? – Smectites in layers in local lows – fluvial deposition? Altered ash fall? – Doublet unit unconformably overlies layered smectites, evidence of change in aqueous geochemistry? Need to resolve doublet mineralogy – Doublet also found alone or mixed with smectites in landslides. Perhaps doublet formed by second period of aqueous alteration on trough floor. Would explain both landslides with and without smectite. – Hydrated silica most recent alteration mineral. Transported short distances by sapping channel flow. Sourced from top of wall rock