Ancient Lunar Crust: Origin, Composition, and Implications

Samples from the Apollo (USA) and Luna (Soviet) missions and from lunar meteorites, coupled with remote sensing data, reveal that the ancient highlands of the Moon are compositionally diverse. The average surface material contains 80 vol% plagioclase. A major suite of rocks, the ferroan anorthosites, averages 96 vol% plagioclase. The feldspathic composition reflects plagioclase flotation in a magma ocean. Late-stage REE-rich magma pooled in the Procellarum region of the lunar nearside. The concentration of heat-producing elements in this region triggered mantle melting and overturn of the cumulate pile, forming two more suites of chemically distinct highland rocks, the magnesian and alkali suites.