ORBITAL EVIDENCE FOR MORE WIDESPREAD FELDSPATHIC ROCKS ON MARS
Here we use data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board NASA's Mars Reconnaissance Orbiter to further characterize the spatial distribution of feldspathic materials. Feldspars with minor Fe substitution can be identified through a diagnostic crystal field absorption in the shortwave-infrared range sensed by CRISM, but only where more Fe-rich phases (olivine, pyroxene) are relatively scarce. More complete mapping of the Nili Patera caldera now allows us to estimate the true extent of evolved igneous compositions in this portion of the Syrtis Major volcanic construct. In the southern highlands, Wray et al. (2013) reported feldspathic outcrops across an area of ~150,000 km2; through continued mapping of highland crater floors, we are now finding similar materials across a swath of terrain >10 times as wide. Applying similar spectral analyses globally will provide a much-improved perspective on what this surprisingly widespread rock type implies about the evolution of Mars.