Geochemistry and Petrology of the Moon: New Insights from New Missions

Clementine and Lunar Prospector extended knowledge gained from samples, including lunar meteorites, to a global scale and provided context to better frame concepts such as the magma ocean and giant-impact bombardment. Results of ongoing and future missions will increase understanding of differentiation processes and subsequent modification by impacts, and will provide critical tests in areas currently poorly understood or not known. From surface compositional distribution, the crust appears laterally heterogeneous on broad scales, with ancient feldspathic highlands best exposed in the northern farside and southern nearside; however, the composition of the lower crust outside the Procellarum KREEP Terrane is poorly known. Ferroan-anorthositic (FA) components dominate many brecciated feldspathic meteorites but the extent to which this is an upper-crustal signature is unclear. Whether mafic rocks observed in crater central peaks represent magnesian intrusives or ferroan complements to the upper crustal FA rocks is not established. Magnesian granulites occur in many breccias, but their origin and role in the lunar crust, and that of rarer magnesian anorthosites, are not known. Rock compositions in the South Pole–Aitken Basin will provide a key test of lower crustal composition, but current remote sensing cannot distinguish if these are ferroan or magnesian. The most fractionated lunar rocks are also not well understood in geologic context. Aristarchus Crater excavated chemically evolved rocks; these and volcanic “red spots” probably include granite (rhyolite) and monzogabbro, but improvements in knowledge await detailed geologic site investigations. Understanding of the apparently olivine- and Fe,Ti,Th-rich basalts of western Procellarum awaits better remote sensing. Remotely sensed mineralogy and geochemistry will be improved by Kaguya's high-spatial-resolution multiband imager, Chandrayaan's M3 hyperspectral imager, LRO's wide-angle camera (including UV bands), better gamma-ray and x-ray data from Kaguya and Chandrayaan, and high-resolution topography from all missions for improved geologic context and photometric corrections for deriving compositions.