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

Abstract

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 Schrödinger 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.

Lunar Mantle Composition Based on Spectral and Geologic Analysis of Low‐Ca Pyroxene‐ and Olivine‐Rich Rocks Exposed on the Lunar Surface

“…As shown above, all the LCP‐rich areas are located on freshly exposed geological features that are less affected by space‐weathering and soil development (e.g., steep slopes of peaks such as mountain peaks, central peaks, and peak rings; slopes of walls, terraces, and rims of impact craters; and ejecta deposits in smaller craters), but not on regolith mixtures. These characteristics are the same as those of olivine‐rich rock areas, where olivine‐rich spectra correspond to fresh geological features such as steep slopes of peaks and impact craters (Yamamoto et al., 2022). Thus, a direct comparison of the global distribution of LCP‐rich and olivine‐rich points would provide constraints on what materials were excavated from deeper (likely the upper mantle) by the formation of impact basins.…”

“…The white dashed circle is an area drawn around the topographic central depression (Ohtake et al, 2014). B6) of the Schrödinger basin, respectively, showing the same trend as the olivine-rich points in this basin (e.g., Kramer et al, 2013;Yamamoto et al, 2012bYamamoto et al, , 2022. Figure 5c shows the Lyman crater (site S-E) and the Antoniadi crater (site S-D), where LCP-rich points are clustered at central peaks and peal rings of the two craters.…”

“…For the stratigraphic analysis, we used the mineral map analysis reported by Yamamoto et al. (2022), which is based on the MI multiband data combined with the Digital Terrain Model (DTM) obtained by TC (Haruyama et al., 2008). This method uses a mineral parameter map M ( i , j ) to give the spatial distribution of specific areas with olivine‐rich, plagioclase‐rich, and pyroxene‐rich spectra in the MI image.…”

“…The details of the mineral map analysis are described by Yamamoto et al. (2022); the algorithm for calculating M ( i , j ) and determining ultramafic LCP end‐member spectra is outlined as follows.…”

“…The relationship between the specific areas dominated by each mineral and the geological structure is used to examine the geological context of each LCP-rich point found by the global survey. The details of the mineral map analysis are described by Yamamoto et al (2022); the algorithm for calculating M(i, j) and determining ultramafic LCP end-member spectra is outlined as follows.…”