Geology topics

Paul G. Lucey

Publications and source records attributed to Paul G. Lucey.

5 recordsLinked to original sources

USGS2019

The compositions of the lunar crust and upper mantle: Spectral analysis of the inner rings of lunar impact basins

The innermost ring in impact basins exposes material originating from various depths, and can be used to study the composition of the lunar crust with depth. In this study, we conduct quantitative mineralogical analyses of the innermost ring in 13 lunar impact basins using reflectance data from the Kaguya Multiband Imager and radiative transfer modeling. We use results from recent hydrocode modeling to calculate the depth of origin of the material exposed by the innermost rings. We find that the most abundant rock type on the innermost ring of most basins is anorthosite. The mafic assemblages are dominated by olivine in some cases, but most often by pyroxene. The impact modeling suggests that the innermost ring material was excavated from a wide range of depths. Here we focus on two mean depths: a crustal component and a mantle component. The crustal component largely dominates the innermost ring material, and the mantle component is present on the innermost ring of 9 of the basins we studied. On these 9 rings, the abundance of low-calcium pyroxene decreases with the proportion of crustal component, suggesting a dominantly mantle origin. However, as we do not detect exposures of ultramafic material, such mantle material is possibly present at the sub-pixel scale (<62 m). This quantitative study reassesses the composition of the lunar crust and upper mantle, which is of great importance for understanding the formation of the Moon.

Planetary and Space Science↗

USGS2012

Spectral properties of ice‐particulate mixtures and implications for remote sensing: 1. Intimate mixtures

The spectral properties of water ice-particulate mixtures are studied for the purpose of deriving the ice and particulate abundances from remotely obtained spectra (particulates referring to nonicy materials in the form of grains). Reflectance levels and ice absorption band depths are a complex function of the single scattering albedo of the particulates embedded in the ice. The ice absorption band depths are related to the mean optical path length of photons in ice through Beers law, Fresnel reflection from the ice-crystal faces on the surface, and ice absorption coefficient as a function of wavelength. Laboratory spectra of many ice-particulate mixtures are studied with high-, medium-, and low-albedo particulates. From the laboratory spectra the band depth, the continuum reflectance, and the ratio of band depth to continuum reflectance are derived for each particulate albedo as a function of the logarithm of the particulate weight fraction in the sample. Ice band depths are dependent on the particulate albedo and increase with smaller weight fractions of particulates until the bands saturate and their depths decrease. The continuum reflectance is a complex function of the particulate albedo and wavelength of light, while the band depth to continuum reflectance ratio appear independent of particulate albedo such that, for a given grain size of particulate, a calibration curve to abundance of ice and particulates is derived. The derived abundance calibrations are accurate if the source of scattering is dominated by particulates and not ice-vacuum (air) interfaces. If ice-vacuum interfaces are dominant, then the derived particulate abundance is an upper limit. Theoretically produced frost spectra show similar curves of growth of band depth, continuum reflectance, and corresponding ratio versus the photon mean optical path length similar to that for intimate mixtures of ice and high-albedo particulates. In all scattering cases the ice absorption coefficients determine the path length needed to produce a given band depth; thus different absorptions are sensitive to different amounts of particulates, with the 3-μm fundamental being the most sensitive to the presence of ice (very low ice abundance) and the 1.04-μm overtone being the most sensitive to the presence of particulates (very high ice abundance).

Journal of Geophysical Research: Solid Earth↗

USGS2011

The Mairan domes: silicic volcanic constructs on the Moon

The Mairan domes are four features located in northern Oceanus Procellarum at ∼312.3E, 41.4N on the Moon. High resolution visible imagery, visible-to-mid-IR spectra, and Lunar Prospector Th abundance data all indicate that these four domes have a composition that is consistent with derivation from a Si-rich, highly evolved magma.

Geophysical Research Letters↗

USGS2008

Composition and origin of the Dewar geochemical anomaly

Dewar crater is a 50-km diameter impact structure located in the highlands northwest of the South Pole–Aitken basin on the lunar farside. A low-albedo area with enhanced Th and Sm values is centered east-northeast of Dewar crater. This area also exhibits elevated FeO abundances (9.0–16.6 wt %) and TiO 2 values (0.6–2 wt %). The range of FeO and TiO 2 abundances determined for the darkest portions of the geochemical anomaly overlap the range of FeO and TiO 2 values determined for nearside mare basalt deposits. Analysis of Clementine spectra obtained from the darkest portions of the Dewar geochemical anomaly indicates that the low-albedo materials contain large amounts of high-Ca clinopyroxene consistent with the presence of major amounts of mare basalt. Cryptomare deposits have played an important role in the formation of the Dewar geochemical anomaly. The evidence indicates that buried basalt, or cryptomare, was excavated from depth during impact events that formed dark-haloed craters in the region. We show that an early Imbrian- or Nectarian-age, low-TiO 2 mare basalt deposit with enhanced Th concentrations (6–7 μ g/g) exists in the Dewar region. This ancient mare unit was buried by ejecta from Dewar crater, creating a cryptomare. Although most mare units on the central farside of the Moon exhibit low Th abundances, the enhanced Th values associated with the Dewar cryptomare deposit indicate that at least some portions of the underlying lunar interior (mantle and crust) on the farside of the Moon were not Th poor.

Journal of Geophysical Research E: Planets↗

USGS2006

Remote sensing studies of the Dionysius region of the Moon

The Dionysius region is located near the western edge of Mare Tranquillitatis and is centered on Dionysius crater, which exhibits a well-developed dark ray system. Proposed origins for these dark rays included impact melt deposits and dark primary ejecta. The region also contains extensive deposits of Cayley-type light plains. Clementine multispectral images and a variety of spacecraft photography were utilized to investigate the composition and origin of geologic units in the Dionysius region. The portions of the dark rays for which spectral and chemical data were obtained are composed of mare debris contaminated with minor amounts of highland material. Both five-point spectra and values of the optical maturity (OMAT) parameter indicate that the dark rays are dominated by mare basalts, not glassy impact melts. The high-albedo rays associated with Dionysius exhibit FeO and TiO2 values that are lower than those of the adjacent dark ray surfaces and OMAT values that indicate that bright ray surfaces are not fully mature. The high-albedo rays are bright largely because of the contrast in albedo between ray material containing highlands-rich ejecta and the adjacent mare-rich surfaces. The mafic debris ejected by Dionysius was derived from a dark, iron-rich unit exposed high on the inner wall of the crater. This layer probably represents a mare deposit that was present at the surface of the preimpact target site. With one possible exception, there is no evidence for buried mare basalts associated with Cayley plains in the region.

Journal of Geophysical Research E: Planets↗