Mapping the Martian Geologic Record: Studies of the Gusev Crater Spirit Landing Site and Plagioclase Feldspar Compositions on Mars

The flurry of activity involved in the scientific study of Mars has resulted in multiple new data sets from several missions (Mars Global Surveyor (MGS), Mars Odyssey (MO), Mars Exploration Rovers (MER), Mars Reconnaissance Orbiter (MRO), and Mars Express) that provide information for unlocking the planet’s geologic and climatic history.

This three part study utilized both orbital data and laboratory experiments to examine Mars for morphologic and mineralogic evidence of aqueous activity and magmatic evolution.

The first study examined Gusev Crater, landing site for the Spirit MER rover. This work began during final landing site selection and was published just prior to Spirit’s January 2004 landing. In this work, I examined the paradigm that Gusev once held a paleolake and that it contains detrital sediment from the northern highlands. Analyses involved using the most current data then available. I produced thermophysical, morphological, and surface unit maps showing the spatial distribution and stratigraphic relationships of materials on the floor of Gusev. Orbital analyses found no unambiguous evidence of paleolake deposits. This study offered alternative hypotheses explaining floor units, one of which, volcanic deposition, has since been verified by Spirit on the ground.

The second and third studies address our ability to accurately derive plagioclase compositions on Mars and to use thermal emission spectroscopy to map vii the distribution of plagioclase compositions on Mars. Plagioclase is the most abundant mineral in the martian crust and may provide information about the igneous evolution and subsequent alteration of the Martian surface. The second study focuses on mixtures more complex in nature than the two-component (composition) plagioclase sand mixtures used in previous work. Linear deconvolutions of laboratory spectra from mixtures involving additional components and phases were used to calculate average plagioclase compositions whose accuracies were found to be comparable to previous studies. The final project carried results from previous laboratory studies one step further to map the global distribution of plagioclase compositions on Mars. Maps reveal a world dominated by labradorite and bytownite, with lesser amounts of other plagioclase. Localized variations are difficult to discern at the scale of individual MGS Thermal Emission Spectrometer (TES) observations.