1. Analysis of phyllosilicate deposits in the Nili Fossae region of Mars: Comparison of TES and OMEGA data
- Author
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Michalski, Joseph, Poulet, FrancOis, Bibring, Jean-Pierre, and Mangold, Nicolas
- Subjects
Clay minerals -- Comparative analysis ,Basalt -- Comparative analysis ,Rocks, Metamorphic -- Comparative analysis ,Mars (Planet) -- Comparative analysis ,Astronomy -- Comparative analysis ,Phyllosilicates -- Comparative analysis ,Mineralogy -- Comparative analysis ,Astronomy ,Earth sciences - Abstract
To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.09.006 Byline: Joseph Michalski (a), Francois Poulet (a), Jean-Pierre Bibring (a), Nicolas Mangold (b) Keywords: Mars, Surface; Mineralogy; Spectroscopy; Infrared observations Abstract: Diverse phyllosilicate deposits discovered previously in the Nili Fossae region with near infrared reflectance data are a window into the complex history of aqueous alteration on Mars. In this work, we used thermal infrared data from the Thermal Emission Spectrometer (TES) in combination with near infrared data from the Observatoire pour la Mineralogie, l'Eau, les Glaces, et l'Activite (OMEGA) to better constrain the mineralogy and geologic origin of these deposits. We developed a TES spectral index for identification of clay minerals, which correctly identifies the phyllosilicates in the Nili Fossae area and points to several other interesting deposits in the Syrtis Major region. However, detailed inspection of the TES spectral features of Nili Fossae phyllosilicates shows a feature at low wavenumbers (350-550cm.sup.-1) that is not an exact match to any specific Fe.sup.3+-, Al-, or Mg-rich phyllosilicate phase. Instead, the feature is more similar to basaltic glass and may indicate that the phyllosilicates in this region are: (1) rich in Fe.sup.2+ (based on similarity to trends seen in laboratory data of clay minerals), (2) poorly crystalline/extremely disordered, and/or (3) present within a matrix of actual basalt glass. This feature is similar to spectral features seen in altered rocks in the Columbia Hills region of Gusev Crater by previous authors. By calibrating measured spectral index values against mathematical spectral mixtures of typical martian dark surfaces and known abundances of alteration minerals, we are able to estimate an enrichment in abundance of alteration minerals in the altered surfaces. Many dark, Noachian deposits in the Nili Fossae area are enriched phyllosilicates by 20-30% ([+ or -]10-15%) relative to dark, volcanic surfaces in the same region. The distribution and abundance of these phases indicates that alteration in the region was pervasive, but did not completely erase the original mineralogy of what was likely an Fe-rich basalt protolith. As a group, the Nili Fossae phyllosilicate deposits are fundamentally different from those found in the Mawrth Vallis region. Nili Fossae deposits have strong thermal infrared features related to admixed pyroxene, plagioclase, and occasionally olivine, whereas the Mawrth Vallis deposits contain no mafic minerals. Comparison of TES and OMEGA data also illustrates some more general differences between the datasets, including the impact of physical character of the martian surface on detectability of minerals in each spectral range. Author Affiliation: (a) Institut d'Astrophysique Spatiale, BAcentstiment 121, Universite Paris Sud, Orsay Cedex 91405, France (b) Lab. de Planetologie et Geodynamique, UMR6112, CNRS et Universite de Nantes, 2 rue de la Houssiniere, BP 92208, 44322 Nantes Cedex 3, France Article History: Received 2 May 2009; Revised 28 August 2009; Accepted 3 September 2009
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- 2010