Northwest Africa 773: Lunar Mare Breccia with a Shallow-formed Olivine- Cumulate Component, Very-low-ti Heritage, and a Kreep Connection

Introduction: Northwest Africa 773 is one of the more unusual lunar meteorites found in recent years because it contains a prominent clast lithology, which appears to be an olivine-rich cumulate [1-4] and because it is a very-low-Ti (VLT) mare breccia with relatively high incompatible-trace-element concentrations and LREE/HREE enrichment [3]. A lunar origin was verified by Fagan and coworkers [2] on the basis of noble-gas contents, oxygen isotopes, and mineral compositions. Fagan et al. described two lithologies: (1) heterolithic impact breccia with a regolith component and (2) cumulus olivine gabbronorite. Here, we refer to these as the breccia (Bx) lithology and the olivinecumulate (OC) lithology. Breccia Olivine OC Parent A14 Green Matrix Cumulate Eq RM Avg A&B FB-EMPA FB-EMPA + 40% Ol [5,9] SiO2 46.2 44.8 44.53 44.62 TiO2 0.78 0.24 0.59 0.71 Al2O3 10.6 3.1 7.05 6.88 Cr2O3 0.40 0.39 0.20 0.53 FeO 17.3 18.1 20.7 20.8 MnO 0.26 0.27 0.26 0.30 MgO 13.2 27.1 18.2 17.6 CaO 10.8 6.01 8.28 8.03 Na2O 0.23 0.03 0.22 0.16 K2O 0.10 0.02 0.04 0.02 P2O5 0.09 0.05