TWO COMPOSITIONALLY DISTINCT OLIVINE-ENRICHED UNITS IN TYRRHENA TERRA AND LIBYA MONTES, MARS

Olivine-rich terrains are prevalent on Mars and some regions have increased amounts of olivine that readily can be identified using orbital remote sensing data. Areas of enhanced olivine in our study region on Mars are present across Tyrrhena Terra (TT) and in the southern rim of the Isidis basin in the Libya Montes (LM). Using near-infrared Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data and mid-infrared Thermal Emission Spectrometer (TES) and Thermal Emission Imaging Spectrometer (THEMIS) data to initially characterize our study site, the strongest olivine signatures across TT are identified in isolated crater floor deposits, while the olivine in the LM area is associated with a stratigraphic unit. Using mid-IR spectral indices developed from synthetic olivine laboratory data for 13 different olivine compositions in the forsterite (Fo₁₀₀) to fayalite (Fo₀) solid solution series, specific Mg-Fe olivine compositions were determined for this study area of Mars. Crater-floor olivine located across TT was determined to be Fo₅₀ and the LM olivine is Fo₆₅. Near-infrared data corroborated these lower- and higher-Mg values. Because these olivines are distinct both compositionally and spatially, their emplacement must be temporally distinct; however, they both could be related to separate events associated with the nearby Syrtis Major volcanic complex. Further analyses of CRISM, TES, THEMIS, High Resolution Stereo Camera (HRSC), High Resolution Imaging Science Experiment (HiRISE), Context Camera (CTX), and Color and Stereo Surface Imaging System (CaSSIS) data will address the emplacement process(es), such as lava flows or ash-fall deposits, and the overall geologic setting of the two distinct olivine-enriched units.