THEMIS Observations and TES Surface Compositions of Low-Albedo Intracrater Materials and Wind Streaks in Western Arabia Terra

High-resolution thermal infrared images (100m/pixel) from the Mars Odyssey Thermal Emission Imaging System (THEMIS) are used for thermophysical analyses of low-albedo intracrater materials and wind streaks in Western Arabia Terra and comparisons with Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) derived surface compositions. Atmospherically corrected thermal emissivity data from TES have been used to identify two global-scale spectral surface units. The Surface Type 1 end-member is interpreted as largely unweathered basalt while the Surface Type 2 end-member has been interpreted as andesite and/or partly weathered basalt. Deconvolved TES spectra of low-albedo intracrater materials reveal both Surface Type 1 and 2 compositions within individual craters. Surface Type 1 compositions form a central core in dark features on crater floors while Surface Type 2 compositions form a surrounding arc on the dark downwind sides of crater walls. The transition between these compositions appears to occur near the floor-wall interface and is correlated with a transition from high-thermal inertia dune materials to low thermal inertia dune-free materials. Surface Type 1 and 2 compositions are also observed in adjacent low albedo wind streaks; however, a mixing trend is not as evident as within the impact craters. THEMIS day/IR observations of low-albedo intracrater materials appear to show relatively lower average temperatures for Surface Type 1 compared to Surface Type 2 while THEMIS night/IR observations appear to reveal higher average temperatures for Surface Type 1 compared to Surface Type 2. There does not appear to be a discernable temperature trend for surface materials in adjacent low-albedo wind streaks. Temperature variations observed in THEMIS images can be produced by a combination of topographic (solar heating) and thermophysical (thermal inertia and albedo) effects; however, combining multiple datasets can minimize uncertainties. The transition from Surface Type 1 to Surface Type 2 intracrater materials is interpreted to reflect decreasing particle sizes controlled by mineralogic differences between an unweathered basalt component and an andesite/altered basalt component. Relatively coarse dune materials are cool (dark) during the day while finer dune-free materials are warmer (bright). Intracrater floor materials are interpreted as eolian sediment blown into craters while wall materials are interpreted as either eolian sediment sorted by particle size, or eroded material from in-place crater wall lithologies.