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  • GEOPHYSICS  (121)
  • ASTROPHYSICS  (108)
  • 1985-1989  (229)
  • 1988  (229)
  • 1
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    Pan-African alkali granites and syenites of Kerala as imprints of taphrogenic magmatism in the South Indian shield (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Granite and syenite plutons with alkaline affinities ranging in age from 550 to 750 Ma sporadically puncture the Precambrian granulites of the Kerala region. All the bodies are small (20 to 60 sq km), E-W to NW-SE elongated elliptical intrusives with sharp contacts and lie on or close to major late Proterozoic lineaments. Geochemical plots of A-F-M and An-Ab-Or relations show an apparent alkali enrichment trend on the former, but the plutons define relatively distinct fields on the latter. Most of the plutons are adamellitic to granitic by chemistry. The variations of SiO2 with log sub 10 K2O/MgO (1) brings out the distinct alkaline nature of the plutons. Some of the granites are extremely potassic, like the Peralimala pluton, which shows up to 11.8 percent K2O. On a SiO2-Al2O3-Na2O+K2O (mol percent) plot, the plutons vary from peraluminous to peralkaline, but none are nepheline normative. Low MgO, low to moderate CaO and high Fe2O3/FeO values are other common characteristics. Among trace elements, depletion of Ba, Sr and Rb with high K/Ba and K/Rb values are typical. Overall, the plutons show a trend of decreasing K/Rb ratio with increasing K content. Individual plutons show more clearly defined trends similar to those from granitic masses characterized by plagioclase fractionation.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., Workshop on the Deep Continental Crust of South India; p 156-158
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  • 2
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    Expected IPS variations due to a disturbance described by a 3-D MHD model (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The variations of interplanetary scintillation due to a disturbance described by a three-dimensional, time-dependent, MHD model of the interplanetary medium are calculated. The resulting simulated IPS maps are compared with observations of real disturbances and it is found that there is some qualitative agreement. It is concluded that the MHD model with a more realistic choice of input conditions would probably provide a useful description of many interplanetary disturbances.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 36; 1155-116
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  • 3
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    The stellar composition of X-ray surveys from the Einstein Observatory (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A new class of X-ray-luminous 'yellow' stellar objects which contributes significantly to the stellar log N-log S distribution, but which cannot be reconciled with normal G and K main-sequence stars. This identification results from a new analysis of the stellar content of three samples of X-ray-selected X-ray sources observed with the Einstein Observatory, namely the 'Medium Sensitivity Survey', the 'High Sensitivity Survey', and the 'Hyades Region Survey'. In this paper, both X-ray and optical properties of the stellar samples in these surveys are reported. The actual stellar content of the surveys is compared with predictions based on current knowledge of stellar X-ray luminosity functions and the stellar composition and spatial distribution in the Galaxy. It is shown that a plausible identification for the excess population of 'yellow' stars is with the active, RS CVn-like binaries.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 324; 1010-101
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  • 4
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    Long-term temporal variability of Cygnus X-2 (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Observations of the low-mass binary X-ray source Cyg X-2 taken over a five-year period using instruments on OSO 8, HEAO 1, and Einstein are presented. Irregular changes in intensity of up to 60 percent on time scales ranging from minutes to days are seen. The source appears to have long-term low-luminosity states during which dips lasting about three days occur. When these long dips occur, they always appear at the same phase in the optically determined 9.8-day orbital period. There are three distinct types of short-term dips distinguished by differing correlations between spectral hardness and intensity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 329; 276-289
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  • 5
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    Pb isotope constaints on the extent of crustal recycling into a steady state mantle (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Isotopic and geochemical evidence was discussed against recycling of continental crust into the mantle. Element ratios such as Sm/Nd, Th/Sc, and U/Pb in sedimentary masses have remained relatively constant throughout Earth history, and this can only be reconciled with steady state recycling models if new crustal materials added from the mantle have had similar ratios. Such recycling models would also require shorter processing times for U, Th, and Pb through the mantle than are geodynamically reasonable. Models favoring subduction of pelagic sediments as the only recycling mechanism fail to account for the Pb isotopic signature of the mantle. Recycling of bulk crust with Pb isotopic compositions similar to those expected for primitive mantle would be permissable with available data, but there appear to be no plausible tectonic mechanisms to carry this out.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., Workshop on the Growth of Continental Crust; p 62-64
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  • 6
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    Role of zircon in tracing crustal growth and recycling (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Single crystal ion probe ages of zircons is discussed, which allow much better time resolution compared to other geochronological methods, although the technique is not without problems. Rocks from two areas that contain composite zircon populations, including true magmatic zircons as well as a variety of xenocrystic types are described. It is often difficult to distinguish these; xenocrystic zircons, for example, cannot always be identified on the basis of morphology alone. Additional evidence is needed before making age interpretations. Evidence is also presented of zircon growth long after the original time of crystallization, in some cases apparently at temperatures less than 300 C. The spectacular discovery of 4.1 to 4.2 Ga detrital zircons in metaquartzites from the Mount Narryer area of Western Australia is described. Similar zircons with ages as old as 4276 Ma have been found in the nearby Jack Hills area. The source areas or parent lithologies of these zircons have not yet been determined, but the author expects that they may be unrecognized or buried antecedents of the K rich Narryer gneisses. U or Th concentrations of zircon cannot be used to discriminate between felsic and mafic source rocks.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., Workshop on the Growth of Continental Crust; p 51-54
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  • 7
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    Metamorphism of cordierite gneisses from Eastern Ghat Granulite Terrain, Andhra Pradesh, South India (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Cordierite-bearing metapelites of the Eastern Ghat granulite terrain occur in close association of Khondalites, quartzites, calc-silicate rocks and charnockites. Rocks occurring between Bobbili in the north and Guntur in the south of Andhra Pradesh are studied. The association of the mineral and textural relationships suggest the following metamorphic reactions: Garnet + sillimanite + quartz = cordierite, hypersthene + sillimanite + quartz = cordierite, sillimanite + spinel = cordierite + corundum, and biotite + quartz + sillimanite = cordierite + K=feldspar. Generally the minerals are not chemically zoned except garnet-biotite showing zoning when they come in close contact with one another. The potential thermometers are provided by the Fe-Mg distribution of coexisting biotite-garnet and cordierite-garnet. Conflicting interpretation of the P/T dependence of these reactions involving cordierite are due to H2O in the cordierite. The presence of alkali feldspar-quartz assemblage which is common in these gneisses will be constrained from melting only if H2O activity is less than 0.5. The piezometric array inferred is convex towards the temperature array, indicating a rapid and isothermal crustal uplift probably aided by thrust tectonics.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., Workshop on the Deep Continental Crust of South India; p 120-121
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  • 8
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    The 1987 Antarctic ozone hole - A new record low (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: In 1987 the Antarctic springtime total ozone as measured by TOMS was substantially lower than in any previous year. Polar ozone levels began decreasing significantly after a mesoscale transient minimum developed over the Weddell Sea on September 5-7. The total ozone over most of the Antarctic continent decreased to less than 200 DU on September 19, and a region where total ozone was less than 125 DU developed on September 30. The lowest level observed was 109 DU on October 5 near the South Pole, a value 29 DU less than the 1985 previous record low. Compared with previous years the 1987 October zonal mean total ozone is substantially lower poleward of 60 S. Antarctic total ozone in 1987 also showed the greatest rate of ozone decrease as well as the longest persistence of the ozone hole.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 1365-136
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  • 9
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    Gamma-ray observations of Co-56 in SN 1987A (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: During observations of SN 1987A 286 days after the supernova explosion using a JPL high-resolution gamma-ray spectrometer, a line feature was found in the net supernova spectrum at an energy of 1240.8 + or - 1.7 keV, with an intrinsic width of 8.2 + or - 3.4 keV FWHM, and a net flux of 0.0021 + or - 0.0007 photons/sq cm per s. This feature is interpreted as the 1238 keV line from the decay of Co-56 in the supernova remnant. The blueshift and intrinsic broadening of the 1238 keV line are consistent with models incorporating mixing of the radioactive cobalt in the expanding eject.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 334; L81-L85
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  • 10
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    Rayleigh lidar observations of gravity wave activity in the upper stratosphere at Urbana, Ill. (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: During 13 nights of Rayleigh lidar measurements at Urbana, Ill. in 1984 to 1986, thirty-six quasi-monochromatic gravity waves were observed in the 35 to 50 km altitude region of the stratosphere. The characteristics of the waves are compared with other lidar and radar measurements of gravity waves and the theoretical models of wave saturation and dissipation phenomena. The measured vertical wavelengths ranged from 2 to 11.5 km and the measured vertical phase velocities ranged from 10 to 85 cm/s. The vertical wavelengths and vertical phase velocities were used to infer observed wave periods which ranged from 100 to 1000 min and horizontal wavelengths which ranged from 70 to 2000 km. Dominant wave activity was found at vertical wavelengths between 2 to 4 km and 7 to 10 km. No significant seasonal variations were evident in the observed parameters. Vertical and horizontal wavelengths showed a clear tendency to increase with wave periods, which is consistent with recent sodium lidar studies of quasi-monochromatic waves near the mesopause. An average amplitude growth length of 20.9 km for the rms wind perturbations was estimated from the data. Kinetic energy density associated with the waves decreased with height, suggesting that waves in this altitude region were subject to dissipation or saturation effects.
    Keywords: GEOPHYSICS
    Type: NASA-CR-182738 , NAS 1.26:182738
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