The Composition of the Lunar Crust: An In-Depth Remote Sensing View

Abstract

In this dissertation, we investigate the composition of the lunar crust by conducting a quantitative and comprehensive analysis of the mineralogical composition of the central peak in 61 craters and the innermost ring of 18 impact basins, which expose material originating from various depths, using reflectance data acquired by the Kaguya Multiband Imager and Spectral Profiler in the visible and near infrared wavelengths. We also place constraints on the depth of origin of the material exposed by the innermost ring of impact basins using impact modeling code that tracks the fate of tracer particles in the target site. We find that the central peaks in the Feldspathic Highlands Terrane are composed of anorthositic lithologies. The variability of their mafic assemblage suggests that some of them are sampling intrusions of mafic material into that crust, though no ultramafic material was detected that might suggest fully differentiated plutons. The central peaks in the South Pole-Aitken basin indicate mafic compositions at all depths, consistent with the presence of a large differentiated melt sheet that assimilated anorthositic crust and ultramafic mantle. The central peaks in the thorium rich Procellarum KREEP Terrane are composed of lithologies intermediate between the anorthositic material of the Feldspathic Highlands Terrane and the more mafic South Pole- Aitken Basin Terrane. We find that the most abundant rock type is anorthosite on the innermost ring of most basins, consistent with our impact modeling results suggesting that the innermost rings are dominated by crustal material. Models indicate that most basins excavate mantle material and should expose a small proportion of such on their innermost ring. However, we do not detect ultramafic lithologies, thus mantle exposures should be present at the subpixel scale, or intermixed with crustal component. We also produced various datasets that are now available to the lunar community, such as maps of olivine, low- and high-calcium pyroxene, plagioclase, iron and optical maturity parameter at 62 meters per pixel (available from the USGS Astropedia website), and maps of the normal albedo measured by the Lunar Orbiter Laser Altimeter at 3 and 1 km per pixel (available on the Planetary Data System website).