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  • 1
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    Melt segregation from partially molten source regions - The importance of melt density and source region size (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An investigation is conducted regarding the changes expected in the density contrast between basic melts and peridotites with increasing pressure using the limited data available on the compressibilities of silicate melts and data on the densities of mantle minerals. It is concluded that since compressibilities of silicate melts are about an order of magnitude greater than those of mantle minerals, the density contrast between basic melts and mantle minerals must diminish significantly with increasing pressure. An earlier analysis regarding the migration of liquid in partially molten source regions conducted by Walker et al. (1978) is extended, giving particular attention to the influence of the diminished density contrast between melt and residual crystals with increasing source region depth and to the influence of source region size. This analysis leads to several generalizations concerning the factors influencing the depths at which magmas will segregate from their source regions and the degrees of partial melting that can be achieved in these source regions before melt segregation occurs.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; July 10
    Format: text
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  • 2
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    Surface tension of natural silicate melts from 1,200-1,500 C and implications for melt structure (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The surface tension between silicate liquid and gas is measured for four lava compositions (limburgite to andesite) from 1,200 to 1,500 C. It is noted that the magnitude of surface tension (gamma) is in the range 350-370 dynes/cm. Variations found in gamma as a function of liquid composition are small and have no obvious relation to liquid composition. Gamma is also found to vary little with furnace atmosphere - air, Ar, CO2, H2, CO and their mixtures. It is found that a relaxation time of hours to days, depending on temperature, is required before reproducible results can be obtained from originally crystalline starting material. The reproducible temperature dependence of gamma for complex silicate liquid solution is found to be small, positive, and a relatively simple function of liquid composition.
    Keywords: GEOPHYSICS
    Type: Contributions to Mineralogy and Petrology; 76; 1981
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  • 3
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    Abyssal tholeiites from the Oceanographer Fracture Zone. II - Phase equilibria and mixing (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: GEOPHYSICS
    Type: Contributions to Mineralogy and Petrology; 70; 1979
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  • 4
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    Workshop on Magmatic Processes of Early Planetary Crusts: Magma Oceans and Stratiform Layered Intrusions (1981)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The significance of the lunar highland pristine cumulate samples were reevaluated with the aid of the additional insights provided by geologically constrained terrestrial investigations. This exercise involved a review of the state of knowledge about terrestrial and lunar cumulate rocks as well as an enumeration and reevaluation of the processes hypothesized to have been responsible for their formation, both classically and at present.
    Keywords: GEOPHYSICS
    Type: NASA-CR-170108 , NAS 1.26:170108 , LPI-TR-82-01 , Aug 03, 1981 - Aug 06, 1981; Houston, TX; United States
    Format: application/pdf
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  • 5
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    Anomalous auroral electron distributions due to an artificial ion beam in the ionosphere (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Results are reported for the perturbation of the auroral ionosphere by the operation of an ion gun which injected about 100 mA of 25-eV Ar(+) ions at upgoing pitch angles over a discrete auroral arc. The major effects observed were the excitation of intense broadband electric field fluctuations at zero-10 kHz, and the appearance of streaming and isotropic heating in different parts of superthermal electron velocity space. A scenario is explored in which electron runaway or streaming is expected between the trapping speed and the critical velocity for cyclotron interactions with the waves, where the streaming electrons carry the current that would be carried by thermals or energetic electrons in the absence of the waves. A current of about 1.0 microA/sq m is carried by the streaming electrons. The gun-associated electrons were anomalous in the sense that their anisotropy was the opposite of that observed in the natural aurora.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 87; Sept. 1
    Format: text
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  • 6
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    A numerical treatment of melt/solid segregation - Size of the eucrite parent body and stability of the terrestrial low-velocity zone (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Crystal sinking to form cumulates and melt percolation toward segregation in magma pools can be treated with modifications of Stokes' and Darcy's laws, respectively. The velocity of crystals and melt depends, among other things, on the force of gravity (g) driving the separations and the cooling time of the environment. The increase of g promotes more efficient differentiation, whereas the increase of cooling rate limits the extent to which crystals and liquid can separate. The rate at which separation occurs is strongly dependent on the proportion of liquid that is present. The observation of cumulates and segregated melts among the eucrite meteorites is used as a basis for calculating the g (and planet size) required to perform these differentiations. The eucrite parent body was probably at least 10-100 km in radius. The earth's low velocity zone (LVZ) is shown to be unstable with respect to draining itself of excess melt if the melt forms an interconnecting network. A geologically persistent LVZ with a homogeneous distribution of melt can be maintained with melt fractions only on the order of 0.1% or less.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 83; Dec. 10
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  • 7
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    Heavy ion beam-ionosphere interactions - Charging and neutralizing the payload (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Three different electrical charging and neutralization processes were experienced during gun operation in the Argon Release Controlled Studies rocket flights, which carried ion generators to 400-500 km in the nighttime auroral ionosphere: DC charging of the vehicle, brief charging at gun turn-on, and extended oscillatory sequences. The present analysis of these phenomena has determined that, during oscillatory events, the entire environment of a payload could alternate between hot electron and cold electron configurations at rates which may have been in excess of 10 kHz.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 453-471
    Format: text
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