A new look at the Apollo 11 regolith and KREEP

Although the Apollo Il mission landed in Mare Tranquillitatis, similar to 5 0 km from the nearest exposure of highlands, small nonmare particles are co nspicuous in the regolith. The nonmare portion of the Apollo Il regolith is compositionally similar to the Apollo 16 regolith. At both sites most of t he nonmare material is from the feldspathic highlands, but some is mafic im pact-melt breccia with the chemical signature known as KREEP for its high c oncentrations of K, rare earth elements, and P. The composition of the Apol lo 11 regolith corresponds best to a mixture of 66% crystalline mare basalt , 5% orange volcanic glass, 20% material of the feldspathic highlands, 8% K REEP-bearing impact-melt breccia, and 1% meteoritic material. The volcanic- glass and KREEP-bearing melt-breccia components account for the high concen trations of Mg and Cr in the regolith. The mast KREEP-rich sample known fro m Apollo 11, 10085,1187, is an impact-melt breccia that bears a strong text ural and compositional similarity to a unique Apollo 16 melt breccia, 64815 . Although not of the maria, such breccias are also not of the highlands pr ovenance. Global data obtained from orbit show that KREEP-bearing materials are most common at low elevations in the Imbrium-Procellarum region and ar e rare at high elevations. Thus, as at Apollo 16, the KREEP-bearing breccia s of Apollo 11 are probably ejecta from the Imbrium impact into the low-lyi ng, Procellarum KREEP Terrane. On the basis of these observation and others , we suggest that the general acceptance of KREEP as a material of the high lands is not supported by the data and results largely from historical acci dent.