Mapping Mineralogy and Mineral Chemistry of the Moon

Near-IR spectra of lunar materials are strongly affected by both mineral abundance and mineral chemistry. Using a radiative transfer mixing model, we have developed methods to invert reflectance spectra and produce mineral abundances and Mg-number (ratio of Mg to the sum of Mg+Fe) from Clementine data, and from ground-based spectra of the Moon. We have used these data to address the issue of the importance of magnesian material on the Moon. In the Apollo collection, the Mg-suite of mafic plutonic rocks represent cumulates from relatively small magma bodies. These rocks are distinct from ferroan anorthosites in trace element content, as well as major mineralogy and chemistry. However, because these rocks are are either rare or absent in the lunar meteorite collection (presumably dominated by farside rocks), it is reasonable to hypothesize that the Mg-suite is a product of the unique thermal environment of the Th-rich Procellarum KREEP Terrane (PKT). However, our results suggest that magnesian material is more widespread and not confined to the PKT. We find two classes of magnesian material. First, within South Pole Aitken orthopyroxene-rich deposits appear to also be magnesian relative to the rest of the basin. Similar rocks also seem exposed in the western central highlands of the Moon. Second, some portions of iron poor, anorthositic regions on the farside seem to contain magnesian mafic minerals.