Comparisons between phyllosilicate-bearing strata at Mawrth Vallis and Terra Meridiani

1. Comparisons between phyllosilicate-bearing strata at Mawrth Vallis and Terra Meridiani W.H. Farrand1, J.W. Rice2, T.D. Glotch31. Space Science Institute, Boulder, CO; farrand@spacescience.org2. Arizona State University, Tempe, AZ 3. State University of New York at Stony Brook, Stony Brook, NY Southwest Terra Meridiani (“Runcorn” crater): This site has been identified by Wiseman et al. and Newsom et al. (2007) as a potential MSL landing site. It has hydrated phyllosilicate minerals and also morphologic evidence (for example an inverted channel) of fluvial activity. HRSC: h2097_0000 RGB CRISM: msp00004886 Introduction: The Mawrth Vallis region has been identified by the Mars Express OMEGA and MRO CRISM instruments as a region with abundant hydrated phyllosilicate minerals (Bibring et al., 2005; Murchie et al., 2007, Loizeau et al., 2007). Exposures of light-toned, phyllosilicate-bearing layered rocks are areally extensive at Mawrth Vallis. The layered deposits at Mawrth Vallis are Noachian in age. Elsewhere on Mars are hydrated sulfate-bearing layered terrains which are interpreted as late Noachian to early Hesperian in age. In the Terra Meridiani region, both sulfate-bearing and phyllosilicate-bearing rocks have been identified. Thus, the potential exists at Terra Meridiani to examine rocks of fundamentally different composition which could be closer in age than are the hydrated and non-hydrated mantling deposits at Mawrth Vallis. Here we present some preliminary comparisons between some of the phyllosilicate-bearing strata at Mawrth Vallis and phyllosilicate-bearing rocks exposed in southwest Terra Meridiani. Mawrth Vallis Spectral Units: Spectral units identified at Mawrth Vallis include one with 2.2 mm band, nominally a montmorillonite, one with a 2.3 mm band, nominally a nontronite, and a darker toned hydrated (with a 1.9 mm structural water band) material. These materials with their associated high spatial resolution appearance in HiRISE imagery are shown below in Figure 1 in CRISM scene frt00003bfg_07_if1666l. In the 2.5, 1.5, and 1.08 mm composite shown in Fig. 1, the 2.2 mm material appears cyan in color, the 2.3 mm material appears as pink and the dark hydrated material appears as a olive-green color. CRISM: Frt00003bfg_07_if1666l (2.5, 1.5 1.08 mm composite) HiRISE PSP_002074_2025 Figure 3: Phyllosilicate exposures at Runcorn crater in SW Terra Meridiani. Green-toned region in CRISM multispectral scene above represents the phyllosilicate exposures. Spectrum from light-toned area displays Mg/Fe – OH band centered at 2.29 mm. Dark hydrated HRSC: h2229_0001 RGB composite; yellow box indicates position of CRISM frame Figure 4: Frt00007b8b SWIR composite (left) and 1900 nm band depth image (right). Frt00007b8b is centered at 3.3° S, 352.1° E. 2.3 mm (nominally Nontronite) - bearing Figure 1: Spectral/textural units at Mawrth Vallis 2.2 mm (nominally Montmorillonite) - bearing Figure 5: HiRISE scene PSP_005344_1765 within Runcorn crater and close-up of light-toned polygonally fractured surface within it. Close-up is located at ~ 3.03° S, 352.12° E. Figure 2:On the left, from top to bottom are the SWIR color composite (2.5 1.5 and 1.08 mm), the VNIR (7.5, 5.5, 4.5 mm) composite and a DCS version of the VNIR color composite, all for the frt00003bfb scene. Above are CRISM spectra (atmospherically corrected and ratioed to the featureless dark mantle unit) of the major spectral units at Mawrth Vallis. Discussion: To date, only hydrated materials with a 2.3 mm absorption band have been observed within the Runcorn crater locale. Exposures are much more limited than at Mawrth Vallis however. Light toned materials at the Runcorn site are polygonally fractured as are those at Mawrth Vallis. Both sites display signs of late stage fluvial activity (inverted channels). While near the Meridiani hematite site, Runcorn does not have exposures of hematite, nor, apparently, sulfate minerals; however, its proximity to sulfate-rich layered deposits raises the possibility that the phyllosilicate minerals at Runcorn were formed in the latter stages of the “Phyllosian” time [6] and perhaps might represent a time just before a drastic change in the Martian depositional environment. References: [1] Bibring et al. (2005) Science, 307, 1576-1581. [2] Loizeau et al. (2007) J. Geophys. Res., 112, 10.1029/2006JE002877. [3] Murchie et al. (2007) J. Geophys. Res., 112, 10.1029/2006JE002682. [4] Newsom et al. (2007) 2nd MSL Landing Site Workshop. [5] Wiseman et al. 2nd MSL Landing Site Workshop. [6] Bibring et al. (2006) Science, 312, 400-404. Acknowledgements: This work is supported by the NASA Mars Data Analysis Program.