¹Lingzhi Sun,¹Paul G. Lucey
Earth and Planetary Science Letters(in Press) Link to Article [https://doi.org/10.1016/j.epsl.2023.118074]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
Copyright Elsevier

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.

^1,2,3Samuel D. Crossley,²Richard D. Ash,^2,3Jessica M. Sunshine,⁴Catherine M. Corrigan,⁴Timothy J. McCoy
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13959]
¹Lunar and Planetary Institute, USRA, Houston, Texas, USA
²Department of Geology, University of Maryland, College Park, Maryland, USA
³Department of Astronomy, University of Maryland, College Park, Maryland, USA
⁴Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA
Published by arrangement with John Wiley & Sons

Models of planetary core formation beginning with melting of Fe,Ni metal and troilite are not readily applicable to oxidized and sulfur-rich chondrites containing only trace quantities of metal. Cores formed in these bodies must be dominated by sulfides. Siderophile trace elements used to model metallic core formation could be used to model oxidized, sulfide-dominated core formation and identify related meteorites if their trace element systematics can be quantified. Insufficient information exists regarding the behavior of these core-forming elements among sulfides during metamorphism prior to anatexis. Major, minor, and trace element concentrations of sulfides are reported in this study for petrologic type 3–6 R chondrite materials. Sulfide-dominated core-forming components in such oxidized chondrites (ƒO2 ≥ iron-wüstite) follow metamorphic evolutionary pathways that are distinct from reduced, metal-bearing counterparts. Most siderophile trace elements partition into pentlandite at approximately 10× chondritic abundances, but Pt, W, Mo, Ga, and Ge are depleted by 1–2 orders of magnitude relative to siderophile elements with similar volatilities. The distribution of siderophile elements is further altered during hydrothermal alteration as pyrrhotite oxidizes to form magnetite. Oxidized, sulfide-dominated core formation differs from metallic core formation models both physically and geochemically. Incongruent melting of pentlandite at 865°C generates melts capable of migrating along solid silicate grains, which can segregate to form a Ni,S-rich core at lower temperatures compared to reduced differentiated parent bodies and with distinct siderophile interelement proportions.