Abstract
We examine the distribution of Thermal Emission Spectrometer (TES) derived surface compositions in the Oxia Palus region on Mars through highâspatialâresolution mapping and integration with Mars Orbiter Camera and Mars Orbiter Laser Altimeter data sets. We also fit the basalt and andesiteâweathered basalt interpretations of TES surface type 1 and type 2 materials into multiple working hypotheses to describe the origin of surface compositions. A mixing/transition from surface type 1 to type 2 is observed in lowâalbedo regions of southern Acidalia Planitia and may represent either (1) an influx of basaltic sediment from the southern highlands, deposited on and mixed with andesitic volcanics; (2) an influx of waterâtransported basaltic sediment from the southern highlands that was altered and later deposited as a thin sedimentary veneer; or (3) different degrees of weathering of indigenous basalt, marking the geographic extent of submarine alteration of basaltic crust. TES spectra of lowâalbedo intracrater materials reveal that surface type 1 compositions form a central core on crater floors, while type 2 compositions form a surrounding arc on the dark downwind sides of crater walls. Intracrater floor materials are interpreted as eolian sediment, and wall materials are interpreted as either eolian sediment or eroded material from inâplace crater wall lithologies. Surface type 1 and type 2 compositions are also observed in adjacent lowâalbedo wind streaks; however, a mixing trend is not as evident. The Mars Pathfinder landing site and Ares and Tiu Valles source regions are sufficiently blanketed by fineâgrained dust to prohibit the analysis of surface rock compositions.
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