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Geology topics

P. D. Spudis

Publications and source records attributed to P. D. Spudis.

9 recordsLinked to original sources
USGS2012

Global petrologic variations on the moon: A ternary-diagram approach.

A ternary-diagram approach for determination of global petrologic variations on the lunar surface is presented that incorporates valuable improvements in our previous method of using geochemical variation diagrams. This new approach uses a ternary diagram that is subdivided into equally spaced segments along each of its three sides and has a triangular area in its center. The segments are assigned distinct colors that cover the range of the visible spectrum. The apexes are assigned the three primary colors, and the center triangle, which represents equal proportions of the three apexes, is assigned the color gray. The apexes are assigned the average Fe and (Th/Ti) c (ratio normalized to chondrites) compositions of KREEP/Mg-suite rocks, mare basalts, and ferroan anorthosites. The composition of each picture element (pixel) within these Apollo orbital gamma ray databases is used to determine its position within the ternary diagram. The color corresponding to this ternary position is then placed on a classification map at that pixel's position within the orbital databases. Error databases produced for the Fe and (Th/Ti) c data were used to exclude pixels having high errors. The resultant classification map shows spatial transitions among petrologic units, allows direct determination of the relative proportions of each end-member composition in a pixel, and increases the geologic interpretability of these data over that of the individual elemental databases. The classification units correspond remarkably well to observed geologic units, when we consider the spatial resolution (100 km) of the gamma ray spectrometer. Our results are as follows: (1) The highlands contain large areas of relatively pure ferroan anorthosite. (2) The average composition of the upper lunar crust is represented by an “anorthositic gabbro” composition, which supports the “magma-ocean” hypothesis for lunar crustal genesis. (3) KREEP/Mg-suite rocks are a minor fraction of the upper lunar crust. (4) Within the farside highlands, areas of KREEP/Mg-suite rocks coincide mostly with areas of crustal thinning, which are probably areas of KREEP basalt extrusions or localized excavations of Mg-suite rocks or KREEP-rich rocks. (5) Portions of the east limb and farside highlands have considerable amounts of a mafic, chondritic Th/Ti component (like mare basalt) whose occurrences coincide with mapped concentrations of light plains that display dark-halo craters; the presence of this component supports the hypothesis that mare volcanism had occurred within this highland region before the end of final heavy bombardment.

Journal of Geophysical Research Solid Earth↗
USGS2007

Global spatial deconvolution of Lunar Prospector Th abundances

We have completed the first global spatial deconvolution analysis of planetary gamma‐ray data for lunar Th abundances as measured by the Lunar Prospector Gamma‐ray Spectrometer. We tested two different spatial deconvolution techniques – Jansson's method and the Pixon method – and determined that the Pixon method provides superior performance. The final deconvolved map results in a spatial resolution improvement of a factor of 1.5–2. The newly deconvolved data allow us to clearly delineate nearside Th enhancements and depressions, validate enhanced Th abundances associated with specific lunar red spots, and reveal new details of the Th distribution at the Aristarchus plateau.

Geophysical Research Letters↗
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↗
USGS1998

The clementine bistatic radar experiment: Evidence for ice on the moon

Ice deposits, derived from comets and water-bearing meteorites hitting the Moon over geological times, have long been postulated to exist in dark areas near the poles of the Moon. The characteristics of radio waves beamed from the Clementine spacecraft into the polar areas, reflected from the Moon's surface, and received on the large dish antennas of the Deep Space Network here on Earth show that roughly the volume of a small lake (0.9-1.8 km 3 ) of water ice makes up part of the Moon's surface layer near the south pole. The discovery of ice near the lunar south pole has important ramifications for a permanent return to the Moon. These deposits could be used to manufacture rocket propellant and to support human life on the Moon.

Solar System Research↗
USGS1994

The Clementine mission to the Moon: Scientific overview

In the course of 71 days in lunar orbit, from 19 February to 3 May 1994, the Clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths. These data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side. In addition, laser-ranging measurements provided the first view of the global topographic figure of the moon. The topography of many ancient impact basins has been measured, and a global map of the thickness of the lunar crust has been derived from the topography and gravity.

Science↗
USGS1994

Clementine observations of the Aristarchus region of the moon

Multispectral and topographic data acquired by the Clementine spacecraft provide information on the composition and geologic history of the Aristarchus region of the moon. Altimetry profiles show the Aristarchus plateau dipping about 1° to the north-northwest and rising about 2 kilometers above the surrounding lavas of Oceanus Procellarum to the south. Dark, reddish pyroclastic glass covers the plateau to average depths of 10 to 30 meters, as determined from the estimated excavation depths of 100- to 1000-meter-diameter craters that have exposed materials below the pyroclastics. These craters and the walls of sinuous rilles also show that mare basalts underlie the pyroclastics across much of the plateau. Near-infrared images of Aristarchus crater reveal olivine-rich materials and two kilometer-sized outcrops of anorthosite in the central peaks. The anorthosite could be either a derivative of local magnesium-suite magmatism or a remnant of the ferroan anorthosite crust that formed over the primordial magma ocean.

Science↗
USGS1987

Basin-ring spacing on the Moon, Mercury, and Mars

Radial spacing between concentric rings of impact basins that lack central peaks is statistically similar and nonrandom on the Moon, Mercury, and Mars, both inside and outside the main ring. One spacing interval, (2.0 ?? 0.3)0.5D, or an integer multiple of it, dominates most basin rings. Three analytical approaches yield similar results from 296 remapped or newly mapped rings of 67 multi-ringed basins: least-squares of rank-grouped rings, least-squares of rank and ring diameter for each basin, and averaged ratios of adjacent rings. Analysis of 106 rings of 53 two-ring basins by the first and third methods yields an integer multiple (2 ??) of 2.00.5D. There are two exceptions: (1) Rings adjacent to the main ring of multi-ring basins are consistently spaced at a slightly, but significantly, larger interval, (2.1 ?? 0.3)0.5D; (2) The 88 rings of 44 protobasins (large peak-plus-inner-ring craters) are spaced at an entirely different interval (3.3 ?? 0.6)0.5D. The statistically constant and target-invariant spacing of so many rings suggests that this characteristic may constrain formational models of impact basins on the terrestrial planets. The key elements of such a constraint include: (1) ring positions may not have been located by the same process(es) that formed ring topography; (2) ring location and emplacement of ring topography need not be coeval; (3) ring location, but not necessarily the mode of ring emplacement, reflects one process that operated at the time of impact; and (4) the process yields similarly-disposed topographic features that are spatially discrete at 20.5D intervals, or some multiple, rather than continuous. These four elements suggest that some type of wave mechanism dominates the location, but not necessarily the formation, of basin rings. The waves may be standing, rather than travelling. The ring topography itself may be emplaced at impact by this and/or other mechanisms and may reflect additional, including post-impact, influences. ?? 1987 D. Reidel Publishing Company.

Earth, Moon and Planets↗