Surface and crater-exposed lithologic units of the Isidis based as mapped by coanalysis of THEMIS and TES derived data products

The stratigraphy and mineral heterogeneity of surface and crater-exposed deposits in the southwestern portion of the Isidis Basin were investigated using spatial, spectral, visible, and thermophysical data sets from both the Mars Global Surveyor and Odyssey missions. Four THEMIS spectral surface units were identified progressing from the Libya Montes highlands to the inner lowland plains of Isidis Planitia. Lithologic determinations of these spectral units were made by linear deconvolution analysis of TES data. Olivine-rich surface materials correlate with a well-documented high-thermal inertia unit. Based on spatial and stratigraphic relationships interpreted from both crater-exposed and surface exposures, the olivine-rich unit was determined to have formed subsequent to the Isidis Basin forming event. Morphology, occurrence, and linear deconvolution of this unit suggests that it may represent Noachian age to Hesperian age picritic lavas that erupted as early-stage lavas originating from sources such as Syrtis Major, beneath Isidis, and as far as Tyrrhena Patera. These lavas are suggested to have partially filled the basin, based on crater-exposed occurrences, and were subsequently buried by further evolved olivine-poor lavas. Later, these lavas were exposed by erosion and subsequent impacts into the basin. Crater scaling suggests significant infilling of the basin by these lavas that may account for craters with very high d/D ratios and the well-developed positive mass anomaly associated with the basin. This study also demonstrates that the remote sensing of impact craters, in conjunction with surface mapping, is a potent mapping tool for understanding stratigraphy and the petrogenesis of the Martian crust.