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  • 1
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    The distribution and purity of anorthosite across the orientale basin: new perspectives from moon mineralogy mapper data (2013)
    Wiley
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    Publication Date: 2013-08-17
    Description: [1]  The Orientale basin is a multiring impact structure on the western limb of the Moon that provides a clear view of the primary lunar crust exposed during basin formation. Previously, near-infrared reflectance spectra suggested that Orientale's Inner Rook Ring (IRR) is very poor in mafic minerals and may represent anorthosite excavated from the Moon's upper crust. However, detailed assessment of the mineralogy of these anorthosites was prohibited because the available spectroscopic datasets did not identify the diagnostic plagioclase absorption feature near 1250 nm. Recently however, this absorption has been identified in several spectroscopic datasets, including the Moon Mineralogy Mapper (M 3 ), enabling the unique identification of a plagioclase-dominated lithology at Orientale for the first time. Here we present the first in-depth characterization of the Orientale anorthosites based on direct measurement of their plagioclase component. In addition, detailed geologic context of the exposures is discussed based on analysis of Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) images for selected anorthosite identifications. The results confirm that anorthosite is overwhelmingly concentrated in the IRR. Comparison with non-linear spectral mixing models suggests that the anorthosite is exceedingly pure, containing 〉95 vol% plagioclase in most areas, and commonly ~99-100 vol%. These new data place important constraints on magma ocean crystallization scenarios, which must produce a zone of highly pure anorthosite spanning the entire lateral extent of the 430 km diameter IRR.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 2
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    New observational evidence of global seismic effects of basin-forming impacts on the Moon from Lunar Reconnaissance Orbiter Lunar Orbiter Laser Altimeter data (2012)
    Wiley
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    Publication Date: 2012-06-05
    Description: New maps of kilometer-scale topographic roughness and concavity of the Moon reveal a very distinctive roughness signature of the proximal ejecta deposits of the Orientale basin (the Hevelius Formation). No other lunar impact basin, even the just-preceding Imbrium basin, is characterized by this type of signature although most have similar types of ejecta units and secondary crater structures. The preservation of this distinctive signature, and its lack in basins formed prior to Orientale, is interpreted to be the result of seismically induced smoothing caused by this latest major basin-forming event. Intense seismic waves accompanying the Orientale basin-forming event preceded the emplacement of its ejecta in time and operated to shake and smooth steep and rough topography associated with earlier basin deposits such as Imbrium. Orientale ejecta emplaced immediately following the passage of the seismic waves formed the distinctive roughness signature that has been preserved for almost 4 billion years.
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  • 3
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    Global surface slopes and roughness of the Moon from the Lunar Orbiter Laser Altimeter (2011)
    Wiley
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    Publication Date: 2011-02-03
    Description: The acquisition of new global elevation data from the Lunar Orbiter Laser Altimeter, carried on the Lunar Reconnaissance Orbiter, permits quantification of the surface roughness properties of the Moon at unprecedented scales and resolution. We map lunar surface roughness using a range of parameters: median absolute slope, both directional (along-track) and bidirectional (in two dimensions); median differential slope; and Hurst exponent, over baselines ranging from ∼17 m to ∼2.7 km. We find that the lunar highlands and the mare plains show vastly different roughness properties, with subtler variations within mare and highlands. Most of the surface exhibits fractal-like behavior, with a single or two different Hurst exponents over the given baseline range; when a transition exists, it typically occurs near the 1 km baseline, indicating a significant characteristic spatial scale for competing surface processes. The Hurst exponent is high within the lunar highlands, with a median value of 0.95, and lower in the maria (with a median value of 0.76). The median differential slope is a powerful tool for discriminating between roughness units and is useful in characterizing, among other things, the ejecta surrounding large basins, particularly Orientale, as well as the ray systems surrounding young, Copernican-age craters. In addition, it allows a quantitative exploration on mare surfaces of the evolution of surface roughness with age.
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  • 4
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    Goldschmidt crater and the Moon's north polar region: Results from the Moon Mineralogy Mapper (M3) (2011)
    Wiley
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    Publication Date: 2011-02-04
    Description: Soils within the impact crater Goldschmidt have been identified as spectrally distinct from the local highland material. High spatial and spectral resolution data from the Moon Mineralogy Mapper (M3) on the Chandrayaan-1 orbiter are used to examine the character of Goldschmidt crater in detail. Spectral parameters applied to a north polar mosaic of M3 data are used to discern large-scale compositional trends at the northern high latitudes, and spectra from three widely separated regions are compared to spectra from Goldschmidt. The results highlight the compositional diversity of the lunar nearside, in particular, where feldspathic soils with a low-Ca pyroxene component are pervasive, but exclusively feldspathic regions and small areas of basaltic composition are also observed. Additionally, we find that the relative strengths of the diagnostic OH/H2O absorption feature near 3000 nm are correlated with the mineralogy of the host material. On both global and local scales, the strongest hydrous absorptions occur on the more feldspathic surfaces. Thus, M3 data suggest that while the feldspathic soils within Goldschmidt crater are enhanced in OH/H2O compared to the relatively mafic nearside polar highlands, their hydration signatures are similar to those observed in the feldspathic highlands on the farside.
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  • 5
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    Compositional variability of the Marius Hills volcanic complex from the Moon Mineralogy Mapper (M3) (2011)
    Wiley
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    Publication Date: 2011-05-12
    Description: Using the Moon Mineralogy Mapper(M3), we examine the Marius Hills volcanic complex for the first time from 0.46 to 2.97 μm. The integrated band depth at 1 μm separates the mare basalts on the plateau in two units: (1) a strong 1 μm band unit of localized lava flows within the plateau that has similar olivine-rich signatures to those of the nearby Oceanus Procellarum and (2) a weaker 1 μm band unit that characterizes most of the basalts of the plateau, which is interpreted as having a high-calcium pyroxene signature. Domes and cones within the complex belong to the high-calcium pyroxene plateau unit and are associated with the weakest 1 μm band observed on the plateau. This difference could be the result of higher silica content, more opaque minerals, and/or a weaker olivine content of the magma. Finally, the floor of Marius crater has one of the strongest olivine-rich signatures of the entire Marius Hills complex. These compositional differences are indicative of the long and complex volcanic history of the region. The first episode started before the emplacement of the surrounding basalts of the plateau and produced the high-calcium pyroxene flows present on the plateau and their associated domes and cones. The second episode occurred concurrently or slightly after the emplacement of the adjacent Procellarum basalts and produced the olivine-rich basalts seen within the plateau, outside the plateau, and in Marius crater. If the olivine content of the lava flows increases with time, the olivine-rich region on the floor of Marius crater may represent one of the latest episodes of volcanism exposed on the Marius Hills complex.
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  • 6
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    Compositional diversity at Theophilus Crater: Understanding the geological context of Mg-spinel bearing central peaks (2011)
    Wiley
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    Publication Date: 2011-06-02
    Description: Analysis of high resolution Moon Mineralogy Mapper (M3) data reveals the presence of a prominent Mg-spinel-rich lithology in the central peaks of Theophilus crater on the lunar nearside. Other peak-associated lithologies are comprised of plagioclase, olivine, and pyroxene-bearing materials. A consistent spatial association of Mg-spinel with mafic-free anorthosite is recognized. Documentation of Theophilus central peaks brings the global inventory of Mg-spinel-rich lithology to two widely separated occurrences, namely Theophilus on the lunar nearside and Moscoviense basin on the farside. The Theophilus crater target region lies on one of the inner rings of the Nectaris basin, indicating that the Mg-spinel-bearing lithology source was deep in the lunar crust.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 7
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    The mineralogy of late stage lunar volcanism as observed by the Moon Mineralogy Mapper on Chandrayaan-1 (2011)
    Wiley
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    Publication Date: 2011-04-26
    Description: The last major phases of lunar volcanism produced spectrally unique high-titanium basalts on the western nearside of the Moon. The Moon Mineralogy Mapper (M3) on Chandrayaan-1 has provided detailed measurements of these basalts at spatial and spectral resolutions necessary for mineralogical interpretation and mapping of distinct compositional units. The M3 imaging spectrometer acquired data in 85 spectral bands from ∼430 to 3000 nm at 140 to 280 m/pixel in its global mapping mode during the first half of 2009. Reflectance data of several key sites in the western maria were also acquired at higher spatial and spectral resolutions using M3's target mode, prior to the end of the Chandrayaan-1 mission. These new observations confirm that both fresh craters and mare soils within the western high-Ti basalts display strong 1 μm and weak 2 μm absorptions consistent with olivine-rich basaltic compositions. The inferred abundance of olivine is observed to correlate with stratigraphic sequence across different mare regions and absolute ages. The apparent stratigraphic evolution and Fe-rich compositions of these basalts as a whole suggest an origin from evolved residual melts rather than through the assimilation of more primitive olivine-rich sources. Mare deposits with spectral properties similar to these late stage high-Ti basalts appear to be very limited outside the Procellarum-Imbrium region of the Moon and, where present, appear to occur as small areas of late stage regional volcanism. Detailed analyses of these new data and supporting measurements are in progress to provide further constraints on the mineralogy, olivine abundance, and compositions of these final products of lunar volcanism and the nature and evolution of their source regions.
    Print ISSN: 0148-0227
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  • 8
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    Mg-spinel lithology: A new rock type on the lunar farside (2011)
    Wiley
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    Publication Date: 2011-04-22
    Description: High-resolution compositional data from Moon Mineralogy Mapper (M3) for the Moscoviense region on the lunar farside reveal three unusual, but distinctive, rock types along the inner basin ring. These are designated “OOS” since they are dominated by high concentrations of orthopyroxene, olivine, and Mg-rich spinel, respectively. The OOS occur as small areas, each a few kilometers in size, that are widely separated within the highly feldspathic setting of the basin rim. Although the abundance of plagioclase is not well constrained within the OOS, the mafic mineral content is exceptionally high, and two of the rock types could approach pyroxenite and harzburgite in composition. The third is a new rock type identified on the Moon that is dominated by Mg-rich spinel with no other mafic minerals detectable (
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  • 9
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    Lunar impact basins: Stratigraphy, sequence and ages from superposed impact crater populations measured from Lunar Orbiter Laser Altimeter (LOLA) data (2012)
    Wiley
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    Publication Date: 2012-02-02
    Description: Impact basin formation is a fundamental process in the evolution of the Moon and records the history of impactors in the early solar system. In order to assess the stratigraphy, sequence, and ages of impact basins and the impactor population as a function of time, we have used topography from the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter (LRO) to measure the superposed impact crater size-frequency distributions for 30 lunar basins (D ≥ 300 km). These data generally support the widely used Wilhelms sequence of lunar basins, although we find significantly higher densities of superposed craters on many lunar basins than derived by Wilhelms (50% higher densities). Our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains. The transition from a lunar impact flux dominated by Population 1 to Population 2 occurred before the mid-Nectarian. This is before the end of the period of rapid cratering, and potentially before the end of the hypothesized Late Heavy Bombardment. LOLA-derived crater densities also suggest that many Pre-Nectarian basins, such as South Pole-Aitken, have been cratered to saturation equilibrium. Finally, both crater counts and stratigraphic observations based on LOLA data are applicable to specific basin stratigraphic problems of interest; for example, using these data, we suggest that Serenitatis is older than Nectaris, and Humboldtianum is younger than Crisium. Sample return missions to specific basins can anchor these measurements to a Pre-Imbrian absolute chronology.
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  • 10
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    Recent Ice Ages on Mars: The Role of Radiatively Active Clouds and Cloud Microphysics (2014)
    Wiley
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    Publication Date: 2014-07-03
    Description: Global Climate Models (GCMs) have been successfully employed to explain the origin of many glacial deposits on Mars. However, the Latitude Dependent Mantle (LDM), a dust-ice mantling deposit that is thought to represent a recent “Ice Age”, remains poorly explained by GCMs. We reexamine this question by considering the effect of radiatively active water-ice clouds (RACs) and cloud microphysics. We find that when obliquity is set to 35°, as often occurred in the past 2 million years, warming of the atmosphere and polar caps by clouds modifies the water cycle and leads to the formation of a several centimeter-thick ice mantle poleward of 30° in each hemisphere during winter. This mantle can be preserved over the summer if increased atmospheric dust content obscures the surface and provides dust nuclei to low-altitude clouds. We outline a scenario for its deposition and preservation that compares favorably with the characteristics of the LDM.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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