Understanding Crust and Regolith Evolution on Mars through Compositional, Thermophysical and Contextual Analyses of Bedrock Exposures

Global acquisition of infrared spectra and high-resolution visible and infrared imagery has enabled the combination of compositional information with stratigraphic and geologic context. Using spectral, thermophysical and morphologic information, we assess the local and regional stratigraphy of the martian surface in an effort to reconstruct the geologic history of the ancient highlands. Mare Serpentis, a representative portion of the cratered highlands, is rich in spectral and thermophysical diversity and host to numerous isolated exposures of bedrock. Most martian surfaces are dominated by fines that bear an uncertain compositional and spatial relationship to their source. Location and characterization of rock units is important for understanding the origin of highland materials and the processes which have modified those materials. The martian highlands in Mare Serpentis are dominated by two interspersed surface units, which have distinct compositional and thermophysical properties: olivine- and pyroxene-rich bedrock and olivine- and pyroxene-depleted sediment or indurated material. This is a major, previously unrecognized trend which appears to be pervasive in the Mare Serpentis region and possibly in other highland areas. The detailed observations have led us to form two hypotheses for the relationship between these two units: either 1) they are related through a widespread mechanical and/or chemical alteration process, where less-mafic plains materials are derived from the mafic bedrock, but have been compositionally altered in the process of regolith formation, or 2) they represent two distinct lithologic units that significantly contributed to the formation of the upper crust. Existing observations suggest that the second scenario is more likely. In this scenario, plains materials represent degraded, and possibly altered, “basement” rock, whereas the bedrock exposures represent later additions to the crust and are probably volcanic in origin. These hypotheses should be further testable with decimeter-resolution imagery and meter-resolution short wavelength infrared spectra.