Assessing Chemical Weathering Trends Derived from Thermal IR Spectral Models: Implications for Chemical Weathering on Mars

Thermal infrared (TIR) spectral models from TES and Mini-TES data have been used to assess the chemical weathering environment on Mars by identifying the primary igneous minerals that dissolve, the secondary products that precipitate, and deriving bulk chemical trends of rocks and soils. APXS data from martian landers show evidence for acidic chemical weathering with low water-to-rock ratios, resulting in the dissolution of olivine and the precipitation of Fe-oxides, Fe-sulfates, and amorphous silica. TIR spectral models from martian orbiters are used to show acidic chemical weathering is a planet-wide process (Hurowitz and McLennan, 2007). Our studies of terrestrial weathered basalt show chemical weathering can cause non-linear mixing in TIR spectral models and the misidentification of the minerals present in weathered rocks. This may lead to inaccurate bulk chemical models derived from TIR spectral models and inaccurate interpretations of the chemical weathering environment. The identification of chemical weathering trends through TIR model-derived bulk chemistry has not been extensively studied. Chemical weathering trends in the Baynton basalt from southeastern Australia are well known (Eggleton et al., 1987 and Nesbitt and Wilson, 1992). Here, we compare the mineralogy and bulk chemistry derived from TIR spectral models of fresh and weathered Baynton basalt to the actual mineralogy and bulk chemistry previously studied to determine whether the mineralogical and chemical trends from weathering can be seen in spectral models. We find that while the TIR model-derived mineral and bulk oxide abundances do not match the actual abundances, the model-derived chemical trends are similar to the actual chemical weathering trends. We will examine the spectral shapes and models to explain why the inaccurate TIR models show the correct weathering trends.