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 ProcessesOct 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.

Hydrated silica

Louros Valles headwall FRT00009998

Louros Valles mouth HRS0000B8EB

Tyrrhena

Mouth

Headwall

Opal (library)

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

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)

Elevation Contour -4200 m -3500 m

Sulfates

Kieserite

PHS

Doublet

Hydrated silica found overlying PHS, probably sourced from sapping channelHydrated silica layer < few m thickThin layer of loose, non-hydrated dark material only partially fills cracks (arrow)

FRT00008950 and PSP_005940_1710

Hydratedsilica

Sulfate150 m

Sulfate and hydrated silica

1

2

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

500m across 180m across

Nontronite-bearing unit

Polygonally fractured but no layering or relief exposed.

Doublet material-bearing unit

Nontronite in thin layers overlain by doublet material. In one case doublet unconformably drapes nontronite.

Layered Smectite clays

Kieserite

PHS

Doublet

HiRISEPSP_006718 colorized with FRT000085A4 (RGB: 2.5, 1.5, 1.08 μm)

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

FRTBFE4 FRT9B27 FRTA202 FRT823A

Layered Smectite clays

Nontronite (green) and doublet (blue)

FRT00009B27, looking SNontronite (green) at higher elevation than doublet. Adjacent obs showsdoublet 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

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

Next slide

Smectite and Doublet

Doublet

FRT27E2 FRTA396

FRT905B

Distinctive variegated color

HiRISE next page

Doublet-only material: located in older landslides or in basement breccia?

Landslides of hydrated material

PSP_006652_1725, overlapping FRTA396

Folds, fractures, and megabreccia blocks. All with 1.4, 1.9, 2.22, and 2.27 μm abs.Images ~250 m across

Landslides of hydrated material

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