Basaltic andesite, altered basalt, and a TES-based search for smectite clay minerals on Mars

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Abstract

The global-scale surface type 2 unit first identified with the Mars Global Surveyor Thermal Emission Spectrometer (TES) remains enigmatic. Competing hypotheses suggest that it represents either basaltic andesite or some form of altered basalt rich in dioctahedral smectite clay minerals and/or spectrally similar amorphous silica phases. Common dioctahedral smectites contain a diagnostic feature in a portion of TES spectra that has been excluded in previous studies because of atmospheric CO2 absorption. We exploit the relative transparency of this spectral region to develop two indices that in tandem, distinguish between certain smectites and amorphous phases. Smectites are not detected in northern lowlands type 2 settings, consistent with other datasets, but the case for primary or secondary amorphous silica phases is strengthened. Separately, one index reveals an abundance of isolated type 2 occurrences in the southern high-latitudes (>50°) associated with dunes, the other shows olivine concentrations between -40° and +30°.

Original languageEnglish (US)
Article numberL10204
JournalGeophysical Research Letters
Volume34
Issue number10
DOIs
StatePublished - May 28 2007

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andesite
thermal emission
montmorillonite
basalt
smectite
mars
clays
clay mineral
Mars
spectrometer
minerals
spectrometers
silica
silicon dioxide
Mars Global Surveyor
dunes
atmospheric attenuation
olivine
transparency
polar regions

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

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abstract = "The global-scale surface type 2 unit first identified with the Mars Global Surveyor Thermal Emission Spectrometer (TES) remains enigmatic. Competing hypotheses suggest that it represents either basaltic andesite or some form of altered basalt rich in dioctahedral smectite clay minerals and/or spectrally similar amorphous silica phases. Common dioctahedral smectites contain a diagnostic feature in a portion of TES spectra that has been excluded in previous studies because of atmospheric CO2 absorption. We exploit the relative transparency of this spectral region to develop two indices that in tandem, distinguish between certain smectites and amorphous phases. Smectites are not detected in northern lowlands type 2 settings, consistent with other datasets, but the case for primary or secondary amorphous silica phases is strengthened. Separately, one index reveals an abundance of isolated type 2 occurrences in the southern high-latitudes (>50°) associated with dunes, the other shows olivine concentrations between -40° and +30°.",
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