The source and origin of the exotic component and KREEP-rich materials on the moon

The enrichments of trace-element concentrations in lunar soils are attributed to the combined effects of comminution of local rocks and a preferential addition of the exotic component to finer grain sizes. The exotic component appears similar to Fra Mauro materials, and there is a strong correlation between the percentage of exotic component and distance from the Fra Mauro site. Based on trace-element characteristics, it is suggested that the exotic component is finely comminuted KREEP and is dispersed on the lunar surface from the Fra Mauro and other high gamma-ray active regions in the Imbrium-Procellarum regions. The major and trace-element chemistry of these materials is considered to be due to impact melting of trace-element-rich accessory phases followed by variable dilution with partial melts of the bulk solid phases of plagioclase, low-Ca pyroxene, and olivine. The generation of KREEP and the exotic component is an impact-produced local process and need not imply a global occurrence of radioactive crust on the moon.