U-Pb zircon dating of the lunar meteorite Dhofar 1442

Dhofar 1442 is one of the few lunar KREEP-rich meteorites, which contains KREEP norites and KREEP gabbronorite as well as low-Ti basalts and highly evolved granophyres. Zircon is a typical accessory mineral of KREEP rocks. U-Th-Pb dates of 12 zircon grains (four of them were in two lithic clasts, and the others were fragments in the meteorite matrix) indicate that the zircons belong to at least two groups of different age: “ancient” (～4.31 Ga) and “young” (～3.95 Ga), which correspond to two major pulses of KREEP magmatism in the source region of the Dhofar 1442 meteorite. The zircon of the “young” group was most probably related to the crater ejecta of the Mare Imbrium Basin. The rock fragments dated at approximately 3.95 Ga have the composition of KREEP gabbronorite. The parental rocks of the zircon of the “ancient” group in the Dhofar 1442 meteorite are uncertain and could be highly evolved granophyres. This hypothesis is supported by the high Th (100–300 ppm) and U (150–400 ppm) contents. These zircon fragments of the “ancient” group, higher than in the “young” group (<50 ppm Th and <70 ppm U) and are typical of zircon from lunar granitic rocks. The composition of the products of KREEP magmatism in the source region of the Dhofar 1442 meteorite could vary from predominantly granitic to KREEP gabbronoritic at 4.3–3.9 Ga.