Identification of quartzofeldspathic materials on Mars

A unique spectral component has been identified near and on the central peaks of two 30 km diameter craters in northern Syrtis Major. These exposures are clearly visible in Thermal Emission Imaging System (THEMIS) color radiance images as well as THEMIS and Thermal Emission Spectrometer (TES) surface emissivity data. Both TES and THEMIS data indicate the presence of increased 1050-1250 cm(-1) (similar to8-9.5 mum) absorption compared to the surrounding basaltic plains, and TES data also display other absorptions at 400, 470, and 800 cm(-1) (similar to25, 20, and 12 mum) consistent with the presence of quartz. Ratio and isolated central peak spectral unit spectra match laboratory emissivity spectra of granitoid rocks composed primarily of quartz and plagioclase feldspar. Deconvolution results also indicate that the surface contains quartz and feldspar in addition to a high-Si glass and/or sheet silicate component. Because central peak materials are brought up from depth during the cratering event, the association of the quartzofeldspathic mineralogy with the central peaks of the craters indicates that the quartz-bearing material was excavated from depth. The occurrence in the two adjacent craters may imply a granitoid pluton of considerable extent. A plausible formation mechanism for this relatively silicic material may be similar to that of terrestrial trondhjemites, which do not require plate tectonics. The rarity of the exposures implies that the process that formed the granitoid composition was probably not widespread. The presence of quartz-bearing material on Mars indicates that mechanisms that produce highly differentiated magmas have been present and extends the diversity of surface compositions identified.