LUNAR MARE DEPOSITS ASSOCIATED WITH THE ORIENTALE IMPACT BASIN: NEW INSIGHTS INTO MINERALOGY, HISTORY, MODE OF EMPLACEMENT, AND RELATION TO ORIENTALE BASIN EVOLUTION FROM MOON MINERALOGY MAPPER (M3) DATA FROM CHANDRAYAAN-1

Carle Pieters pioneered reflectance spectroscopy of lunar mare deposits and the Moon Mineralogy Mapper (M³) experiment, of which she is PI, has now provided image and spectral reflectance data to assess mare deposits in detail. We use M³ data to analyze the distribution, age, mode of emplacement of units with mare basalt affinities in and adjacent to the Orientale multi-ring impact basin, and to assess models for the relationships of basin formation and evolution and mare basalt genesis and emplacement. Mare basalt emplacement began prior to Orientale as evidenced by cryptomaria. Earliest maria occur in the center, postdating Orientale by ~60-100 Ma. Over the next several hundred million years, basalt patches were emplaced first along the base of the Outer Rook ring (Lacus Veris) and then along the base of the Cordillera ring (Lacus Autumni), with some overlap in ages. Analysis of various spectral parameters show few distinct differences in basalt mineralogy in Mare Orientale; rather, differences are due primarily to vertical and lateral mixing with subjacent and adjacent feldspathic basin deposits. Mare patches in Lacus Veris and Autumni show a range of spectral characteristics indicating differences in original basalt mineralogy and mixing with Orientale deposits. The new data show several previously undetected mare patches in SW Orientale. We attribute the trend in distribution to increasing crustal and lithospheric thickness to the SW, with correspondingly deeper density and thermal barriers to basaltic magma ascent and eruption. The wide range of ages of Orientale mare deposits mirrors the wide range of nearside mare ages; this indicates that the small amount of mare fill in Orientale is not due to early cessation of mare emplacement, but rather to limited volumes of extrusion for each phase during the entire period of nearside mare basalt volcanism. This suggests that nearside and farside source regions may be similar, but that other factors, such as thermal and crustal thickness barriers to magma ascent, may be determining the abundance of surface deposits on the limbs and farside. No clear evidence is found to support models of impact basin pressure-release melting. The sequence, timing and elevation of mare basalt deposits suggest that regional basin-related stresses exerted control on their distribution.