The extent of phyllosilicates in the northern highlands around Mawrth Vallis: CRISM observations of Western Arabia Terra

Details The extent of phyllosilicates in the northern highlands around Mawrth Vallis: CRISM observations of Western Arabia Terra The extent of phyllosilicates in the northern highlands around Mawrth Vallis: CRISM observations of Western Arabia Terra

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p13d1560n&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P13D-1560

Physics

3672 Planetary Mineralogy And Petrology (5410), 5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars

Scientific paper

The largest spatial exposure of phyllosilicates on the surface of Mars occurs on the highland plains around Mawrth Vallis. It extends for about 300 kilometers southward from the edge of the dichotomy boundary, covering an area of over 200 x 300 km (e.g., Poulet et al 2005; Noe Dobrea and Michalski 2006; Loizeau et al 2007) over an elevation range of ~2000 m. At least two different types of phyllosilicates (Fe/Mg smectites, and Al smectites), presenting complex spatial and stratigraphic relationships, have been identified in OMEGA data. Stratigraphically, the phyllosilicate-bearing units appear exposed from under a darker, indurated, and more heavily cratered unit, suggesting that it has recently been exhumed (Michalski and Noe Dobrea, 2007) from under an overlying unit. It is unclear, however, whether the clay-bearing units extend into the southern highlands and into the northern lowlands. In this investigation, we use both OMEGA spectral cubes (~1 km/pixel) and CRISM multispectral data sampled at 256 pixels per degree and map projected into 5-degree tiles (~230 m/pixel) to further constrain the extent of phyllosilicates in the Mawrth Vallis region. We find a good correlation between the spatial distribution of phyllosilicates as detected by CRISM and OMEGA, where coverage overlaps. We identify additional small, localized phyllosilicate exposures in CRISM tiles in places up to 100 km farther than the boundaries previously identified with OMEGA. These exposures are found around craters to the south, in interior deposits of a crater to the east, and in association with hummocks in the lowlands to the north. Additional phyllosilicate signatures are observed in darker materials at the base of the escarpment that constitutes the dichotomy boundary in this area. The exposures show spatial variability of the 2.2- and 2.3-μ m absorptions, suggesting complex spatial and stratigraphic relationships similar to those previously observed in the largest exposures. The identification of phyllosilicate exposures in the southern highlands may suggest that the clay-bearing unit observed around Mawrth Vallis is in fact an exposure of a much more extensive clay unit that may underlie at least part of the southern highlands. Additionally, the identification of phyllosilicates in some of the hummocks of the northern lowlands suggests that these hummocks may be erosional remnants of a formerly more extensive unit, leading to the possibility that the dichotomy boundary has erosionally regressed.

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