Mineralogy of the lunar crust: Results from Clementine

Abstract

Abstract-The central peaks of 109 impact craters across the Moon are examined with Clementine ultraviolet-visible (UVVIS) camera multispectral data. The craters range in diameter from 40 to 180 km and are believed to have exhumed material from 5-30 km beneath the surface to form the peaks, including both upper 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 parameters, including "key ratio" (which is related to mafic mineral abundance) and "spectral curvature" (linked to absorption band shape, which distinguishes between low-and high-Ca pyroxene and olivine). The spectral parameters are correlated to mineralogical abundances, related in turn to highland plutonic rock compositions. The derived rock compositions for the various central peaks are presented in a global map. From these results, it is evident that the lunar crust is compositionally diverse, both globally and at local 100 m scales found within individual sets of central peaks. Although the central peaks compositions imply a crust that is generally consistent with previous models of crustal structure, they also indicate a more anorthositic crust than generally assumed, with a bulk plagioclase content of -8 1%, evolving from "pure" anorthosite near the surface towards more mafic, low-Ca pyroxene-rich compositions with depth (comparable to anorthositic norite). Evidence for mafic plutons occurs in both highlands and basins and represent all mafic highland rock types. However, the lower crust is more compositionally diverse than the highlands, with both a greater range of rock types and more diversity within individual sets of central peaks.

Spectral properties of the Marius Hills volcanic complex and implications for the formation of lunar domes and cones

“…Plagioclase feldspar, the most abundant mineral in lunar highland rocks, is spectrally characterized by a continuous upward slope from the 415 to the 900 nm channel and then shows a decrease in reflectance between 900 and 1000 nm because of an absorption band at 1300 nm [Tompkins and Pieters, 1999]. Fresh highlands appear blue because they have a higher 415/750 value, which is the ratio displayed in the blue channel, compared to mature highlands soils.…”

“…Fresh highlands appear blue because they have a higher 415/750 value, which is the ratio displayed in the blue channel, compared to mature highlands soils. Low-Ca pyroxene, which may be intermixed with the anorthosite in highlands rocks, should have an absorption at around 900 nm, slightly shorter than the highCa pyroxene absorption at 1000 nm [Tompkins and Pieters, 1999]. …”

Major lunar crustal terranes: Surface expressions and crust‐mantle origins

“…Despite heavy cratering, there are no broad areas within this region that have elevated FeO concentrations, with the main exception of Mare Moscoviense (Plate 1). Tompkins and Pieters [1999] showed that the central peaks of large craters within the FHT, which expose materials from as deep as 15 km, are dominantly anorthositic. Even some basins (e.g., Freundlich-Sharanov (18.5øN, 175øE), Hertzsprung (1.5øN, 128.5øW), and Korolev (4.5øS, 157øW)) in this region, which would have penetrated some 25-35 km, apparently did not excavate material that was substantially more mafic.…”

Rock types of South Pole‐Aitken basin and extent of basaltic volcanism

“…The original approach developed by Tompkins to distinguish between different mafic-bearing lithologies used two optical parameters to characterize the diagnostic shape of the ferrous band near 1000 nm: band strength (called "key ratio") and band curvature [Tompkins and Pieters, 1999]. In order to easily map the distribution of different lithologic units using the twodimensional data of Clementine color mosaics, we have expanded this scheme to include a third parameter, band tilt.…”