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  • 1
    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
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    In:  J. Geophys. Res., Basel, Birkhäuser Verlag, vol. 91, no. 6-7, pp. 11377-11392, pp. B05S07, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1986
    Keywords: Stress ; Elasticity ; Planetology ; Tectonics ; JGR
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  • 3
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    In:  J. Geophys. Res., Warszawa, Polish Geothermal Association, vol. 84, no. 7, pp. 1667-1682, pp. B05406, (ISSN: 1340-4202)
    Publication Date: 1979
    Keywords: Stress ; Elasticity ; Planetology ; Tectonics ; JGR
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  • 4
    Publication Date: 2016-07-02
    Description: Two competing hypotheses suggest lunar Mg-suite parental melts formed: (1) by shallow-level partial melting of a hybridized source region (containing ultramafic cumulates, plagioclase-bearing rocks, and KREEP), producing a plagioclase-saturated, MgO-rich melt, or (2) when plagioclase-undersaturated, MgO-rich melts were brought to plagioclase saturation during magma-wallrock interactions within the anorthositic crust. To further constrain the existing models, phase equilibria experiments have been performed on a range of Mg-suite parental melt compositions to investigate which composition can best reproduce two distinct spinel populations found within the Mg-suite troctolites—chromite-bearing (FeCr 2 O 4 ) troctolites and the more rare pink spinel (MgAl 2 O 4 or Mg-spinel) troctolites (PST). Phase equilibria experiments at 1 atm pressure were conducted under reducing conditions $$(\mathrm{log}\phantom{\rule{0.4em}{0ex}}{f}_{{\mathrm{O}}_{2}}\sim \mathrm{IW}-1)$$ and magmatic temperatures (1225–1400 °C) to explore the spinel compositions produced from melts predicted by the models above. Additionally, the experimental data are used to calculate a Sp-Ol, Fe-Mg equilibrium exchange coe to cient to correct natural spinel for sub-solidus re-equilibration with olivine in planetary samples: Sp-Ol $${K}_{\mathrm{D}}^{\hbox{ Fe-Mg }}=0.044\mathrm{Cr}{\#}_{\mathrm{sp}}+1.5$$ (R 2 = 0.956). Melts from each model (≥50% normative anorthite) produce olivine, plagioclase, and Mg-spinel compositionally consistent with PST samples. However, chromite was not produced in any of the experiments testing current Mg-suite parental melt compositions. The lack of chromite in the experiments indicates that current estimates of Mg-suite parental melts can produce Mg-spinel bearing PST, but not chromite-bearing troctolites and dunites. Instead, model calculations using the MAGPOX equilibrium crystallization program predict chromite production from plagioclase-undersaturated melts (〈20% normative anorthite). If so, experimental and model results suggest chromite in Mg-suite crystallized from plagioclase-undersaturated parental melts, whereas Mg-spinel in the PST is an indicator of magma-wallrock interactions within the lunar crust (a mechanism that increases the normative anorthite contents of initially plagioclase-undersaturated Mg-suite parental melts, eventually producing Mg-spinel). The constraints for magmatic chromite crystallization suggest Mg-suite parental melts were initially plagioclase-undersaturated. In turn, a plagioclase-undersaturated Mg-suite parent is consistent with mantle overturn models that predict Mg-suite parent magmas resulted from decompression melting of early ultramafic cumulates produced during the differentiation of a global lunar magma ocean.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
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  • 5
    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.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    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.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    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.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    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.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 9
    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
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    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
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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