Mineralogy of the lunar crust: Results from Clementine

The central peaks of 109 impact craters across the Moon are examined with C lementine ultraviolet-visible (UVVIS) camera multispectral data. The crater s range in diameter from 40 to 180 km and are believed to have exhumed mate rial from 5-30 km beneath the surface to form the peaks, including both upp er and lower crustal rocks depending on whether craters have impacted into highlands or basins. Representative five-color spectra from spectrally and spatially distinct areas within the peaks are classified using spectral par ameters, including "key ratio" (which is related to mafic mineral abundance ) and "spectral curvature" (linked to absorption band shape, which distingu ishes between low- and high-Ca pyroxene and olivine). The spectral paramete rs are correlated to mineralogical abundances, related in turn to highland plutonic rock compositions. The derived rock compositions for the various c entral peaks are presented in a global map. From these results, it is evide nt that the lunar crust is compositionally diverse, both globally and at lo cal 100 m scales found within individual sets of central peaks. Although th e central peaks compositions imply a crust that is generally consistent wit h previous models of crustal structure, they also indicate a more anorthosi tic crust than generally assumed, with a bulk plagioclase content of simila r to 81%, evolving from "pure" anorthosite near the surface towards more ma fic, low-Ca pyroxene-rich compositions with depth (comparable to anorthosit ic norite). Evidence for mafic plutons occurs in both highlands and basins and represent all mafic highland rock types. However, the lower crust is mo re compositionally diverse than the highlands, with both a greater range of rock types and more diversity within individual sets of central peaks.