Searching for mantle dunite candidates around the Imbrium basin among the boulder population using high resolution mineral mapping

Abstract

Dunite is a rock type composed of more than 90% olivine, and Mg-rich dunite has been suggested to be a rock type that may represent upper mantle of the Moon. Dunite rocks might have been exposed on basin rings by basin-forming impacts. However, previous studies reported no unambiguous evidence of mantle dunite from lunar samples and remote sensing detections. In this work, we applied a mantle boulder candidate search algorithm around the Imbrium basin using radiative transfer modeling and datasets from Moon Mineralogy Mapper and Multiband Imager. We found two boulders consisting of ∼90 vol% olivine with 95 Mg# on Copernicus central peaks, which are possible mantle dunite excavated by Imbrium basin or Copernicus crater. We also found that non-dunite boulders on Copernicus central peak show a large variation in olivine content (8–51 vol%). We infer this is a result of the complicated process of Mg-suite formation in the lower crust or mechanical mixing during the Imbrium basin forming event. The algorithm we presented has a great potential to be applied to lunar basins for a global search for mantle candidate boulders.