Rock 67015: A feldspathic fragmental breccia with KREEP‐rich melt clasts

Breccia 67015, one of the feldspathic fragmental breccias (FFBs) from the rim of North Ray Crater, contains a wider range of clast lithologies than has been described previously in FFB's. Our petrologic and INAA studies have revealed two components of major petrologic and geologic significance. One of these is a dark, vesicular, KREEP‐rich melt rock of VHA (very high alumina) basalt composition, which occurs in clasts up to 6 cm long. Melt rocks of this type are common at the Apollo 16 site, but in previous years had not been discovered as prominent constituents of the feldspathic fragmental breccias. Their apparent absence led to hypotheses, no longer valid, that the KREEPy melt rocks were younger than the anorthositic breccia matrices and that the two lithologies might represent Imbrian and Nectaris ejecta, respectively. The second lithology we discovered is a large clast of medium‐grained ferroan anorthositic norite with a composition that falls among the most magnesian members of the ferroan anorthosite suite of pristine cumulate rocks. This material constitutes a previously ‘missing’ member of certain mixing models designed to account for the North Ray Crater melt rocks and bulk breccias.