Global Distribution and Geological Context of Co‐Existing Occurrences of Olivine‐Rich and Plagioclase‐Rich Materials on the Lunar Surface

We examined the global distribution and geological context of lunar sites where olivine- and plagioclase-rich materials co-exist. These sites are areas showing plagioclase-rich spectra adjacent to areas showing olivine-rich spectra, and they extend over several hundreds of meters on the lunar surface. From an analysis of the high-spatial-resolution data obtained from the SELENE (Kaguya) multiband imager, we identified 14 co-existing occurrences among 49 olivine-rich sites located around large impact basins. We found that the co-existing occurrences are limited to a few sites among the olivine-rich sites in the Moscoviense, Crisium, and Imbrium basins, while six of seven olivine-rich sites in the Schrodinger basin show co-existing occurrence. The geological features between the co-existing occurrences and the olivine-rich sites without plagioclase-rich materials showed no clear difference, but both types of site are found at fresh geological features located around the peak rings of impact basins. These results may suggest that the co-existing occurrences are closely related to the material heterogeneity of the peak ring regions. The heterogeneity could be formed by mixing of the olivine-rich mantle and the anorthosite-rich crust during impact basin formation, or it might be a reflection of the compositional heterogeneity of the lunar lower crust. For future sample return missions, the detailed information on the co-existing occurrences presented here might be useful for a sampling strategy to select a "one-stop" site that provides important information for the overall characterization of lunar mantle and crustal materials. Plain Language Summary The surroundings of several impact basins on the lunar surface are known to contain olivine-rich sites that are dominated by olivine-rich spectra. Some of these olivine-rich sites co-exist with plagioclase-rich (purest anorthosite) materials, which are adjacent to the olivine-rich materials. The detailed study of these co-existing occurrences would provide critical constraints on the structure, composition, and evolution of the lunar crust and upper mantle. In this study, we examined the global distribution and geological context of co-existing occurrences based on the analysis of the high-spatial-resolution data obtained from the SELENE (Kaguya) multiband imager. Our results showed that the locations of co-existing occurrences are limited to fresh geological features around the peak rings of impact basins, and their spatial distributions are sporadic along the peak rings, suggesting material heterogeneity in these regions. The heterogeneity could be due to mixing of the olivine-rich mantle and anorthositic crust during the formation of the impact basins, or it may reflect a compositional heterogeneity of deep-seated materials in the lower crust. For future sample return missions, the detailed information on co-existing occurrences given here will be useful for a selecting a "one-stop" sampling site to better characterize the lunar mantle and crustal materials.