The composition and history of breccia 67015 from North Ray Crater

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Abstract
We have examined feldspathic fragmental breccia 67015 from the rim of North Ray Crater and found it to be the most diverse and complex of the Apollo 16 FFBs. It contains a wider range of clast types than any of the others and is not dominated by any single lithology. We have identified several crystalline lithologies, occurring in minor amounts, that we believe represent highland plutonic rocks. Plagioclase fragments are the most abundant breccia constituent, followed by clasts of impact melt rocks and granulites. The impact melts are of two main types: feldspathic fragment‐laden melts and mafic, KREEPy melt rocks of VHA basalt composition. Textural evidence indicates that some of the VHA melts were hot and plastic when they accumulated into the breccia. 40Ar‐39Ar dates show that both types of melts solidified about 3.9 × 109 years ago. Magnetic measurements on clasts show a scatter of NMR directions, making it impossible to read a consistent imprint of an ancient dipolar magnetic field. Previous studies of Apollo 16 stratigraphy suggested that KREEPy melt rocks were introduced to the site as Imbrium impact ejecta, about 3.8 × 106 years ago. Our results indicate that the highlands crust contained KREEP components as early as 3.9 × 109 years ago.