USING CRISM AND THEMIS DATA TO CHARACTERIZE MAFIC MINERALOGY IN TYRRHENA TERRA, MARS

The southern highland region of Mars is a prime location in which to study the emplacement and evolution of exposed primary crustal materials on a terrestrial planet. Here, we use Vis/NIR spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to characterize the distribution of mafic-bearing materials, including terrain enriched in olivine, low-calcium pyroxene (LCP), and high-calcium pyroxene (HCP), in the expanse between two large impact basins, Hellas and Isidis. We find that LCP is largely concentrated in erosionally-resistant massifs in the northern Hellas rim region. These LCP-enriched outcrops may be remnants of the lower crust that were uplifted and/or excavated by the Hellas impact. Near the Hellas rim, olivine- and HCP-enriched material is also somewhat concentrated in massif-forming terrain. In a majority of the study region, however, HCP- and olivine-rich material persists in younger, plains-forming deposits that are consistent with high thermal inertia (TI) units previously identified using Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS) data. These plains units are interpreted to result from effusive igneous processes, including widespread fracture-enabled flood volcanism and/or impact-induced decompression melting. Although both olivine and HCP spectral signatures are observed in both intra- and inter-crater plains, HCP enrichment is associated primarily with filled craters, whereas olivine is more prevalent in the vast intercrater plains. By utilizing CRISM mapping data, we are able extend the identification of the THEMIS high TI units to areas that are morphologically and mineralogically similar. We then statistically quantify the differences in thermal inertia and relative spatial abundance of the three mafic minerals within the two types of plains units. We use these differences to constrain possible scenarios for their formation and subsequent modification to present-day attributes. Understanding the nature of the mafic minerals exposed in the Noachian highlands provides crucial insight into the crustal evolution of Mars.