Evidence For Regional-scale Alteration Fronts On Mars: Extent, Stratigraphy, And Mineralogy Of Phyllosilicates Around Mawrth Vallis.

Details Evidence For Regional-scale Alteration Fronts On Mars: Extent, Stratigraphy, And Mineralogy Of Phyllosilicates Around Mawrth Vallis. Evidence For Regional-scale Alteration Fronts On Mars: Extent, Stratigraphy, And Mineralogy Of Phyllosilicates Around Mawrth Vallis.

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.0303n&link_type=abstract

American Astronomical Society, DPS meeting #40, #3.03; Bulletin of the American Astronomical Society, Vol. 40, p.389

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The largest exposure of phyllosilicates on Mars occurs on the highland plains around Mawrth Vallis. This exposure is known to extend almost continuously for about 300 km southward from the edge of the dichotomy boundary, covering an area greater than 200 x 300 km over an elevation range of 2000 m ([1],[2],[3],[4]). At least three different types of hydrated phyllosilicates (Fe/Mg- and Al-phyllosilicates), as well as examples of hydrated silica (e.g., opal-A, hydrated glass), have been identified in OMEGA and CRISM data[1]. These hydrated units are generally associated with layered, indurated light-toned outcrops with complex spatial and stratigraphic relationships, and are unconformably overlain by a darker, indurated, more heavily cratered unit[3]. Recent studies of the light-toned layered units show a mineralogical stratigraphy: the Fe/Mg phyllosilicate-bearing units are overlaying by the Al-phyllosilicate-bearing units, which are in turn overlain by a dark-toned, spectrally unremarkable capping unit ([4],[5],[6]). We have used CRISM, CTX, and HiRISE data to perform a regional study of the distribution of phyllosilicates in the Arabia Terra region, and have found that the same assemblages of hydrous minerals and stratigraphic relationships observed around Mawrth Vallis occur in many erosional windows throughout a 1000x1000 km region, regardless of elevation. The distribution and observed mineralogical relationships suggests that these secondary minerals were not deposited in a basin, but may rather be the product of alteration of primary minerals to Fe/Mg phyllosilicates with subsequent near-surface leaching to Al-bearing phyllosilicates and hydrated silica phases in hydrothermal, pedogenic, or diagenetic settings.
[1] Poulet et al. (2005) Nature 438, 632-627
[2] Noe Dobrea and Michalski (2006) AGU Fall 2006, #P23D-0091
[3] Michalski and Noe Dobrea(2007) Geology,35, pp. 951-954
[4] Loizeau D. et al. (2007) JGR, 112 (E8)
[5] Bishop et al. (2008) Science , in press
[6] Wray et al. (2008) GRL, in press

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