THEMIS AND TES CHARACTERIZATION OF LADON BASIN, SOUTHERN MARGARITIFER TERRA, MARS

Studies have integrated datasets from the Mars Odyssey (MO) and Mars Global Surveyor (MGS) missions with the goal of unraveling the compositional nature of the Martian crust. Here, we continue with this objective. Specifically, we use MO's THermal EMission Imaging System (THEMIS) data supplemented by data from MGS's Thermal Emission Spectrometer (TES), Mars Orbiter Camera (MOC), and Mars Orbiter Laser Altimeter (MOLA) to begin an integrated geologic and spectroscopic study of Ladon basin in southwestern Margaritifer Terra. The express purpose of this work is to characterize the structure, composition, and petrogenesis of the Martian crust in this region.

Centered near 18° S, 330° E, Ladon basin is a 900 km diameter degraded multi-ringed impact crater. The basin walls expose approximately 1.5 km of layered Noachian to Hesperian-aged igneous and/or sedimentary rock. Topographically smooth material characterizes much of the basin floor and it appears to represent a greater than 200 m-thick layered sedimentary deposit emplaced through the channel and valley network systems associated with the basin. Curvilinear troughs that host aeolian bedforms dissect the basin floor materials; the origin of these troughs remains enigmatic, but may reflect the subsurface withdrawal of material. Impact crater ejecta locally covers the basin floor materials and curvilinear troughs.

The basin walls and floor have TES bolometric albedos ranging from 0.11-0.15 and spectrally derived dust cover indices ranging from approximately 0.960-0.980. Together, these values demonstrate the reasonably low dust cover required for spectral determination with THEMIS and TES. Preliminary THEMIS and TES spectroscopic measurements of both the basin walls and topographically smooth basin floor materials are consistent with a basaltic composition. Impact ejecta on the basin floor, which presumably represents a sampling of sub-surface basin floor materials, also shows a basaltic composition. Notable in all preliminary THEMIS measurements of Ladon basin-related materials is an apparent absence of olivine. However, it is not clear if this absence of olivine reflects petrogenetic or weathering processes. Additional work will further refine the composition of materials exposed in Ladon basin with an emphasis on constraining their petrogenesis.