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  • LUNAR AND PLANETARY EXPLORATION  (3)
  • GEOPHYSICS  (2)
  • 1980-1984  (5)
  • 1960-1964
  • 1
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    Anomalies within the system - Rochechouart target rock meteorite (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Contaminated impact crater formations are pertinent to the study of meteoritic contamination at the Cretaceous-Tertiary boundary and other Ir-enriched layers. Target mixing considerations and volumetric estimates of Rochechouart breccias are presently combined with the geochemistry of both major and siderophile trace elements, to evaluate how the chemistry of the preserved target rock-projectile mixture evolved since deposition. Over 99 percent of the mass of extraterrestrial Ir and Os in preserved formations at Rochechouart is located in suevite-like breccias and impact melts. Hydrothermal alteration and/or weathering are the most likely processes to explain both major and trace element redistribution in Rochechouart formations.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Format: text
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  • 2
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    Micas in experimentally shocked gneiss (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Powder-propellant guns are used to shock biotites and muscovites from a gneiss at pressures between 18 and 70 GPa. It is shown that shock in biotite and muscovite can produce homogeneous and devolatilized glasses within microseconds. Shock-deformed micas are found to exhibit fracturing, kinking, and complex extinction patterns over the entire pressure range investigated. Localized melting of micas commences at 33 GPa and reaches completion at 70 GPa. Even though melted biotite and muscovite are opaque optically, they exhibit extensive microvesiculation and flow when observed with the SEM. It is confirmed through electron diffraction that biotite and muscovite have transformed to a glass. The distribution of vesicles in shock-vitrified mica reveals escape of volatiles within the short duration of the shock experiment. It is noted that experimentally shocked biotite and muscovite undergo congruent melting. It is noted that the compositions of the glasses are similar to the unshocked micas except for volatiles (H2O loss and and K loss). These unusual glasses produced from mica can be quenched by rapid cooling conditions during the shock experiment. On the basis of the results, it is pointed out that the extremely low H2O content of tektites can be reconciled with a terrestrial origin by impact.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 89; B685-B69
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  • 3
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    Repeated shock and thermal metamorphism of the Abernathy meteorite (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Based on the example of Abernathy (L6 chondrite), it is shown how petrographic investigation can be used to unravel the nature, chronology and conditions of superposed metamorphic events in chondrites. Features considered include the texture of the rock, optical characteristics of olivine, pyroxene and plagioclase, refractive index of plagioclase, metallographical characteristics and microhardness of Fe-Ni alloys. It is deduced that Abernathy has been involved in at least six metamorphic events since the formation of the chondrite. Four distinct shock events and two separate reheating events have been identified. The chronology of these events is established. The conditions for the last four events are reasonably well constrained. These include severe reheating (T greater than 1200 C); severe shock causing complete melting of plagioclase and local melting of the rock (P between 90 and 110 GPa, T between 1250 and 1350 C); mild shock (P between 10 and 25 GPa, T less than 500 C); and reheating below 800 C.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 19; 29-48
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  • 4
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    Investigation of tidal displacements of the Earth's surface by laser ranging to GEOS-3 (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An analysis of laser ranging data from three stations was carried out in an attempt to measure the geometric Earth tide. Two different approaches to the problem were investigated. The dynamic method computes pass to pass apparent movements in stations height relative to short arcs fitted to several passes of data from the same station by the program GEODYNE. The quasi-geometric method reduces the dependence on unmodelled satellite dynamics to a knowledge of only the radial position of the satellite by considering two station simultaneous ranging at the precise time that the satellite passes through the plane defined by two stations and the center of mass of the Earth.
    Keywords: GEOPHYSICS
    Type: NASA-CR-156863
    Format: application/pdf
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  • 5
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    Shock experiments on maskelynite-bearing anorthosite (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A series of shock recovery experiments over 9.9-60.4 GPa have been carried out on naturally shocked anorthosite from the Mistastin impact structure in Labrador consisting primarily of diaplectic plagioclase glass or maskelynite, An(50), and pyroxene. Petrographic observations of the experimental products indicate that the component minerals and diaplectic glasses generally retained their initial character throughout, the only exception being the increase in fracturing which occurred in the 9.9 GPa shot. Reshocking at pressures higher than the initial shock tends to lower the refractive index of maskelynite. The increase in refractive index of maskelynite reshocked to pressures lower than the initial pressure is interpreted as due to shock densification of the diaplectic glass above the Hugoniot elastic limit and below the mixed phase regime. The data suggest that the low-high-low density transition of maskelynite occurs about 8 GPa below that of the crystal of corresponding composition.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters (ISSN 0012-821X); 68; 1 Ap
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