Mathematics – Logic
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p21c0170w&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P21C-0170
Mathematics
Logic
5410 Composition (1060, 3672), 5464 Remote Sensing, 5470 Surface Materials And Properties, 5494 Instruments And Techniques
Scientific paper
Observations by MGS-TES have greatly improved knowledge of the global distribution of Martian mineral-phase abundances and provide insight to the nature of past geologic environments. Modeling of abundant (~ 25 vol %) high-silica glass (78 wt % SiO2) in ST2 materials was significant in leading to the interpretation of an andesite to basaltic andesite composition for this global endmember. The accurate identification of glass abundances and compositions is thus important for classifying surface lithologies. However, only a few igneous glasses have been analyzed in the laboratory and are available as deconvolution endmembers. The goal of this study is to survey the compositions of potential Martian glasses, establish their spectral character, and assess their importance as endmembers in deconvolutions of Martian thermal infrared spectra. Glasses currently being synthesized include a ST1 analog, similar in composition to terrestrial Deccan flood basalts, and a Fe-rich, Al2O3-poor basaltic Martian meteorite analog. These two basalts offer starting compositions from which to explore the range of interstitial glasses that could be present in Martian basaltic lithologies. Three interstitial melt compositions being made include a glass formed by 90% dry crystallization (56.9 wt % SiO2) and two glasses after 50% and 80% hydrous crystallization (59.8 and 66.2 wt % SiO2). The crystallization of basalts containing no water leads to a specific set of interstitial melt compositions that remain basaltic over large portions of the crystallization sequence because the proportion of SiO2 that plagioclase and pyroxene remove from the melt during crystallization roughly equals the SiO2 content of the initial basalt. The presence of water has a significantly different effect on the composition of interstitial melts of crystallizing basalt. Water hinders crystallization of silicate minerals but does not affect crystallization of Fe-Ti oxides. This shifts the timing of Fe-Ti oxide crystallization to earlier in the crystallization sequence and leads to an early and steady increase in the SiO2 content of interstitial melts. Interstitial melt compositions are initially basaltic, transition to andesitic compositions near ~50% crystallization and to dacitic compositions near ~80% crystallization. Initial linear deconvolutions of ST1 and ST2 spectra with endmember sets including the new 80% hydrous crystallization glass (66.2 wt % SiO2) show both spectra modeled with the new glass endmember (ST1 35 vol %, ST2 20 vol %). The addition of this new phase results in reductions in the amount of modeled plagioclase in both spectra and high-silica glass (78 wt % SiO2) in ST2. Use of the new glass in modeling ST2 shifts the bulk composition of the lithology to lower SiO2 contents, suggesting that the ST2 lithology may be more basaltic in nature. Overall, the significant role of the new interstitial glass in modeling TES spectra indicates the importance of further investigation and characterization of relevant Martian glasses.
Hamilton Victoria E.
Minitti Michelle E.
Wyatt Michael Bruce
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