Synthesis and Analysis of Silicate Glasses: Applications to Remote Sensing of Volcanic Surface Units on Earth and Mars

Introduction: Volcanism is the primary process in the solar system that creates the surfaces of the terrestrial planetary bodies. Volcanoes and volcanic surface units provide information about the geologic history of these bodies, which reflects the unique thermal and chemical evolution of each. Remote sensing provides an effective means to study these volcanic surface units in a quantitative way. Thermal infrared (TIR) is one such type of remotely sensed data set that has been collected for Earth and Mars. TIR data has been used to determine the temperature and emissivity (a material property) of volcanic surfaces [e.g. 1-3] to derive energy output of active volcanoes on Earth [e.g. 4-6], and various emissivity-derived characteristics of volcanic deposits, including material composition and physical state [e.g. 7-15] and surface texture [16-18]. However, a knowledge gap remains in our understanding of the fundamental ways silicate structures (especially in glasses) affect TIR emissivity and how to accurately map emissivity of volcanic surfaces. Glass Synthesis: A preliminary suite of glasses has been synthesized in the Experimental Analysis Laboratory at the University of Western Ontario (Table 1). End-member glasses of microcline (KAlSi3O8), albite (NaAlSi3O8), and andesine (Na0.6Ca0.4Al1.4Si2.6O8) feldspars were created. Additional glasses of quartz (SiO2) and plagioclase feldspar mixtures were synthesized to represent simplified analogs of volcanic glasses, including two “rhyolitic” glasses (59 wt% plagioclase + 41 wt% quartz) and a “dacitic” glass (70 wt% plagioclase + 30 wt% quartz). In order to synthesize each glass sample, constituent minerals were ground to a fine powder (typically 20-members or mixtures were dried at 100oC and then melted at atmospheric pressure in platinum crucibles. The albite end-member glass was quenched from 1550oC; all other glasses were quenched from 1600oC.