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  • 1
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    Constraining the Flux of Impactors Postdating Heavy Bombardment Using U-Pb Ages of Impact Glasses (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Spherules of glass varying in size from a few micrometres to a few millimetres are common in the lunar regolith. While some of these glass beads are products of pyroclastic fire fountains others originate as impact melt ejected from the target that breaks into small droplets and solidifies as spherical particles while raining back to the lunar surface. These glasses preserve information about the chemical composition of the target and often contain sufficient amount of radioactive nuclides such as 40K to enable Ar-40-Ar-39 dating of individual beads. Studies measuring the age of glass beads have been used in attempts to establish variations in the flux of impactors hitting the Moon, particularly during the period that postdates the formation of major impact basins [1,2]. These studies proposed a possibility of spike in the impact flux about 800 Ma [2] and over the last 400 Ma [1]. More recently U-Th-Pb isotopic systems have been also utilized to determine the age of impact glasses from the Apollo 17 regolith [3]. Our aim is to extend the application of the U-Pb system in impact glasses to spherules isolated from Apollo 14 soil 14163 in an attempt to further investigate the applicability of this isotopic system to the chronology of impact glass beads and gain additional information on the impact flux in the inner Solar system.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-27960 , Lunar and Planetary Science Conference; Mar 18, 2013 - Mar 22, 2013; The Woodlands, TX; United States
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  • 2
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    Basin Excavation, Lower Crust, Composition, and Bulk Moon Mass balance in Light of a Thin Crust (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: New lunar gravity results from GRAIL have been interpreted to reflect an overall thin and low-density lunar crust. Accordingly, crustal thickness has been modeled as ranging from 0 to 60 km, with thinnest crust at the locations of Crisium and Moscoviense basins and thickest crust in the central farside highlands. The thin crust has cosmochemical significance, namely in terms of implications for the Moon s bulk composition, especially refractory lithophile elements that are strongly concentrated in the crust. Wieczorek et al. concluded that the bulk Moon need not be enriched compared to Earth in refractory lithophile elements such as Al. Less Al in the crust means less Al has been extracted from the mantle, permitting relatively low bulk lunar mantle Al contents and low pre- and post-crust-extraction values for the mantle (or the upper mantle if only the upper mantle underwent LMO melting). Simple mass-balance calculations using the method of [4] suggests that the same conclusion might hold for Th and the entire suite of refractory lithophile elements that are incompatible in olivine and pyroxene, including the KREEP elements, that are likewise concentrated in the crust.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-27962 , Lunar and Planetary Science Conference; Mar 18, 2013 - Mar 22, 2013; The Woodlands, TX; United States
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  • 3
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    Quantitative EPMA Compositional Mapping of NWA 2995: Characterization, and Petrologic Interpretation of Mafic Clasts (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present the first fully quantitative compositional maps of lunar meteorite NWA 2995 using electron microprobe stage mapping, and compare selected clast mineralogy and chemistry. NWA 2995 is a feldspathic fragmental breccia containing numerous highland fine grained lithologies, including anorthosite, norite, olivine basalt, subophitic basalt, gabbro, KREEP-like basalt, granulitic and glassy impact melts, coarse-grained mineral fragments, Fe-Ni metal, and glassy matrix [1]. Chips of NWA 2995, representing these diverse materials, were analyzed by INAA and fused-bead electron-probe microanalysis (EPMA); comparison of analytical data suggests grouping of lunar meteorites NWA 2995, 2996, 3190, 4503, 5151, and 5152. The mean composition of NWA 2995 corresponds to a 2:1 mixture of feldspathic and mare material, with approximately 5% KREEP component [2]. Clast mineral chemistry and petrologic interpretation of paired stone NWA 2996 has been reported by Mercer et al. [3], and Gross et al. [4]. This study combines advances in quantitative EPMA compositional mapping and data analysis, as applied to selected mafic clasts in a polished section of NWA 2995, to investigate the origin of mafic lithic components and to demonstrate a procedural framework for petrologic analysis.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-38490 , Lunar and Planetary Science Conference; Mar 20, 2017 - Mar 24, 2017; The Woodlands, TX; United States
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  • 4
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    Ar-Ar Thermochronlogy of Apollo 12 Impact-Melt Breccia 12033,638-1 (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We have undertaken an Ar-Ar thermochronology investigation as part of a coordinated multichronometer analysis of a single Apollo 12 impact- melt breccia to demonstrate the wide range of information that can be obtained for a single complex rock. This has implications for the age of formation, component makeup, and subsequent impact/shock and exposure history of the sample. This study also serves as a capabilities demonstration for the proposed MoonRise Mission [1]. The goal of this investigation is to elucidate the history of this sample through coordinated 40Ar*/39Ar, Sm-Nd, Rb-Sr and zircon 207Pb-206Pb ages along with geochemical and petrographic context on a relatively small (approximately 450 mg) sample. Here, we report preliminary results of the Ar-Ar thermochronology.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-38491 , Lunar and Planetary Science Conference; Mar 20, 2017 - Mar 24, 2017; The Woodlands, TX; United States
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