Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31d1727c&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P31D-1727
Physics
[5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Phyllosilicates are detected in a number of contexts on Mars, primarily associated with ancient Noachian terrains. These phyllosilicates deposits may have been altered by multiple processes. Indeed, most ancient phyllosilicate sediments on Earth have experienced a complicated post-depositional history. We hypothesize that dehydrated and/or dehydroxylated phyllosilicates may be present on Martian surface as one of the consequences of widespread impacts and volcanism during the Noachian and early Hesperian periods. The objective of this work is hence to identify, map, and characterize these dehydrated and/or dehydroxylated phyllosilicates on Mars, if any. We have acquired laboratory emission (1400-100 cm-1) and near IR reflectance (1.2-2.5 μm) spectra of heated samples (up to 900 °C) of phyllosilicates and natural zeolites. Our preliminary attempt to combine remote sensing analyses and laboratory investigations related to dehydrated or dehydroxylated phyllosilicates resulted in three interesting observations: (1) Michalski et al. (2010) used TES data to analyze the nontronite deposits in the Nili Fossae region and found that TES spectra consistently exhibited a spectral absorption located near ~450 cm-1 instead of nontronite's characterized spectral features in long-wavelength region. Correspondingly, our laboratory spectral results showed that the doublet or triplet spectral feature in the Si-O bending region of nontronite disappeared at 400 °C and was replaced by one single absorption centered at ~450 cm-1, while notronite kept its weak 1.9, 2.3, and 2.4 μm spectral bands in near IR region; (2) in addition to nontronite, laboratory spectral results provided more suggestive evidence for the scenario that, phyllosilicates could lose all original spectral features in thermal IR region when heated to 700-900 °C, while maintaining their characteristic hydration bands in near IR region in the same temperature range, which could partially be responsible for the difficulty in detecting phyllosilicates on Mars using thermal IR emission spectroscopy. For example, hectorite, saponite, and sepiolite all still maintained diagnostic near IR spectral bands of phyllosilicates at high temperatures (700 °C for hectorite and saponite; 900 °C for sepiolite), while their thermal IR spectra at temperatures of 700 °C or higher were already dominated by spectral bands of enstatite, which are completely different from those of phyllosilicates; (3) laboratory spectral results showed that Mg2+-rich phyllosilicates tend to have a new spectral feature developed at ~920 cm-1 upon heating to 800 °C. Preliminary TES spectral index mapping suggests that altered clays with this ~920 cm-1 feature may be present throughout the northern rim of Hellas Impact Basin. This detection corresponds to the widely distributed Mg2+-phyllosilicates revealed by CRISM observations (~2.31-2.32μm) in the same region.
Che Concong
Glotch Timothy D.
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