Petrology and chemistry of Apollo 12 regolith breccias

Abstract

Petrographic, mineral chemical, and bulk chemical data are reported for the three large Apollo 12 regolith breccias of the regolith breccia suite and for eight breccias handpicked from Apollo 12 coarse fines. Two samples formed from non‐KREEPy anorthositic regolith not presently found at the sampling site. Eight of the samples can be considered mixtures of local basalt and KREEP components, with minor anorthositic components. Mare:KREEP ratios indicated by chemical mixing models range from 86:7 to essentially endmember KREEP. One sample is unlike the others (FeO 23.7; MgO 21.7) and may be a new lithology or alternatively a nonrepresentative sample. Of the 11 samples studied, 5 appear to be of local origin, 3 are most likely exotic to the site, and results for 3 others are inconclusive. The anorthositic breccias formed from Apollo 16‐like regolith and may have been transported over several hundred kilometers from the non‐KREEPy highlands to the east. Alternatively, they may be of local origin, formed from the material beneath the Apollo 12 basalt flows.