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  • 1
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    Styles of zoning in central Andean ignimbrites - Insights into magma chamber processes (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Data are presented showing that calc-alkaline high-K ignimbrites from the Altiplano-Puna Volcanic Complex of the Central Volcanic Zone of the Andes, showing a variety of compositional zonations. The characteristics of the juvenile material from the zoned and heterogenous ignimbrites suggest that crystallization of the observed phenocrysts occurred in prezoned magma chambers consisting of two or more layers. It is suggested that the width/height ratio of a magma chamber plays a critical role in the control of the style of zonation that may develop in a closed magma chamber.
    Keywords: GEOPHYSICS
    Type: ; : Problems in the ae
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  • 2
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    An investigation of the distribution of eruptive products on the shield volcanoes of the western Galapagos Islands using remotely sensed data (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Recent volcanic activity in the Galapagos Islands is concentrated on the two westernmost islands, Isla Isabela and Isla Fernandina. Difficult access has thus far prevented comprehensive geological field studies, so we examine the potential of remotely sensed data as a means of studying volcanic processes in the region. Volcan Wolf is used as an example of the analysis of SPOT HRV-1 data undertaken for each volcano. Landsat TM data are analyzed in an attempt to construct a relative age sequence for the recent eruptive activity on Isla Fernandina. No systematic variation in the surface reflectance of lava flows as a function of age could be detected with these data. Thus it was not possible to complete a study of the temporal distribution of volcanic activity.
    Keywords: GEOPHYSICS
    Type: In: Thematic Conference on Geologic Remote Sensing, 8th, Denver, CO, Apr. 29-May 2, 1991, Proceedings. Vol. 2 (A93-28978 10-43); p. 1161-1174.
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  • 3
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    'Self-consistent' production of ion conics on return current region auroral field lines - A time-dependent, semi-kinetic model (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We describe initial results from a time-dependent, semi-kinetic model of plasma outflow incorporating wave-particle interactions along current-carrying auroral field lines. Electrostatic waves are generated by the current driven ion cyclotron instability (CDICI), causing perpendicular velocity diffusion of ions plus electron heating via anomalous resistivity when and where the relative drift between electrons and ions exceeds certain critical velocities. Using the local bulk parameters we calculate these critical velocities, and so are able to self-consistently switch on and off the heating of the various particle species. Due to the dependence of these critical velocities on the bulk parameters of the species the heating effects exhibit quite complex spatial and temporal variations. A wide range of ion distribution functions are observed in these simulations, including conics with energies of a few electron volts and 'ring' distributions. The rings are seen to be a natural result of transverse heating and velocity filter effects and do not require coherent acceleration processes. We also observe the formation of a density depletion in hydrogen and enhanced oxygen densities at high altitudes.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 10; p. 1841-1844.
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  • 4
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    Iridium and trace element measurements from the Cretaceous-Tertiary boundary, site 752, Broken Ridge, Indian Ocean (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Fourteen samples spanning a 2.5 m interval that includes the Cretaceous-Tertiary (K/T) boundary from Hole 752B near the crest of Broken Ridge in the eastern Indian Ocean were studied in order to search for anomalous enrichments of iridium (Ir) and shock-metamorphosed quartz grains. No allogenic quartz grains larger than 10 microns were observed, hence the presence of quartz containing diagnostic evidence of shock-metamorphism could not be confirmed. Two Ir anomalies of 2.2 +/- 0.6 and 2.0 +/- 0.4 parts per billion (ppb) were measured in samples of dark green ash-bearing chalk at depths of 357.93 and 358.80 m below seafloor, respectively. These samples containing anomalous enrichments of Ir were taken from approximately 82 cm above and 5 cm below the extinction level of Globotruncanids. Our results are consistent with those of Michel et al., who observe elevated concentrations of Ir at these depths in addition to a larger Ir anomaly associated with the extinction level of Globotruncanids.
    Keywords: GEOPHYSICS
    Type: ; : Ultraviolet techno
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  • 5
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    Analysis of atmospheric trace constituents from high resolution infrared balloon-borne and ground-based solar absorption spectra (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Results of ongoing studies of high-resolution solar absorption spectra aimed at the identification and quantification of trace constituents of importance in the chemistry of the stratosphere and upper troposphere are presented. An analysis of balloon-borne and ground-based spectra obtained at 0.0025/cm covering the 700-2200/cm interval is presented. The 0.0025/cm spectra, along with corresponding laboratory spectra, improves the spectral line parameters, and thus the accuracy of quantifying trace constituents. Results for COF2, F22, SF6, and other species are presented. The retrieval methods used for total column density and altitude distribution for both ground-based and balloon-borne spectra are also discussed.
    Keywords: GEOPHYSICS
    Type: In: Remote sensing of atmospheric chemistry; Proceedings of the Meeting, Orlando, FL, Apr. 1-3, 1991 (A93-31376 11-35); p. 194-202.
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  • 6
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    Airborne lidar measurements of ozone and aerosols in the summertime Arctic troposphere (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Ozone (O3) and aerosol distributions were remotely measured from an aircraft using a differential absorption lidar (DIAL) system as part of the 1988 NASA Global Tropospheric Experiment - Arctic Boundary Layer Experiment (ABLE-3A). The airborne DIAL system made simultaneous measurements of O3 and aerosols from the surface to above the tropopause. These measurements were made in a broad range of atmospheric conditions over the tundra, ice, and ocean regions near Barrow and Bethel, Alaska, during July and August 1988. The tropospheric composition over the Arctic was found to be strongly influenced by stratospheric intrusions. Regions of low aerosol scattering and enhanced O3 mixing ratios were usually correlated with descending air from the upper troposphere or lower stratosphere. Several cases of enhanced O3 were observed during ABLE-3A in conjunction with enhanced aerosol layers in the free troposphere resulting from biomass burning. As was found in the Amazon, the products of biomass burning can significantly alter O3 concentrations in the troposphere. This paper describes the NASA airborne DIAL system and discusses the large-scale variations of O3 and aerosols observed with the airborne DIAL system during ABLE-3A.
    Keywords: GEOPHYSICS
    Type: In: Remote sensing of atmospheric chemistry; Proceedings of the Meeting, Orlando, FL, Apr. 1-3, 1991 (A93-31376 11-35); p. 7-14.
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  • 7
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    Earth's mysterious atmosphere. ATLAS 1: Teachers guide with activities (1991)
    In:  CASI
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    Publication Date: 2019-08-28
    Description: One of our mission's primary goals is to better understand the physics and chemistry of our atmosphere, the thin envelope of air that provides for human life and shields us from the harshness of space. The Space Shuttle Atlantis will carry the ATLAS 1 science instruments 296 km above Earth, so that they can look down into and through the various layers of the atmosphere. Five solar radiometers will precisely measure the amount of energy the Sun injects into Earth's environment. The chemistry at different altitudes will be measured very accurately by five other instruments called spectrometers. Much of our time in the cockpit of Atlantis will be devoted to two very exciting instruments that measure the auroras and the atmosphere's electrical characteristics. Finally, our ultraviolet telescope will probe the secrets of fascinating celestial objects. This Teacher's Guide is designed as a detective story to help you appreciate some of the many questions currently studied by scientists around the world. Many complex factors affect our atmosphere today, possibly even changing the course of global climate. All of us who live on Earth must recognize that we play an ever-growing role in causing some of these changes. We must solve this great atmospheric mystery if we are to understand all these changes and know what to do about them.
    Keywords: GEOPHYSICS
    Type: NASA-EP-282 , NAS 1.19:282
    Format: application/pdf
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  • 8
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    Geochemistry and petrogenesis of proterozoic mafic dykes in north Kerala, southwestern Indian Shield - Preliminary results (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Mafic dyke intrusions occur in three distinct orientations ( NNW-SSE and NW-SE and NE-SW) in north Kerala regions, the southwestern part of the Indian Shield. Dating of two NNW-SSE trending dykes by K-Ar method has yielded Middle Proterozoic ages (ca. 1660 Ma and ca. 1420 Ma respectively). Our initial geochemical results on these dyke rocks (0.65-0.15 wt pct K2O, 0.37-0.38 wt pct P2O5, 3.30-1.00 wt pct TiO2, 11-1 p.p.m. Rb, 250-90 p.p.m. Sr, 230-40 p.p.m. Ba, 160-40 p.p.m. Zr, and 30-10 x chondrite rare earth elemental abundances) indicate a transitional character between abyssal and plateau tholeiites. Petrogenetic modelling suggests that the dyke compositions have been derived by different degrees of partial melting of a heterogenous source mantle. The mantle sources with accessory amphibole and/or garnet, variably enriched in LREE and LIL elements, are compatible with the observed geochemical data.
    Keywords: GEOPHYSICS
    Type: Precambrian Research (ISSN 0301-9268); p. 235-244.
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  • 9
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    Caldera-structure relationships in Kenya - Observations from satellite data (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Maps were constructed showing lineaments displayed on four Landsat MSS images, to study volcanic-tectonic relationships in the Kenya segment of the Gregory or eastern sector of the East African rift system. Many of the mapped lineaments correlated well with fractures shown on geological maps. Selected lineaments, transverse to the rift trend, could be extrapolated to intersect rift faults at locations correlative with the locations of Kenya's seven volcanic calderas. The volcano-genetic difference between these intersections vs. similar intersections having no obvious relationship to any type of volcanic vent is not yet understood.
    Keywords: GEOPHYSICS
    Type: 1991 ACSM-ASPRS Annual Convention; Mar 25, 1991 - Mar 29, 1991; Baltimore, MD; United States
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  • 10
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    The biosphere as a driver of global atmospheric change (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The effects of the biosphere on the evolution of atmospheric oxygen and ozone, and the consequences of that development for global atmospheric change, are discussed. Attention is given to the impact of oxygen and ozone on atmospheric photolysis rates, the effect of oxygen on the biogenic production of nitrous oxide and nitric oxide, and the effects of the evolution of atmospheric oxygen on fires and biomass burning. The influence of the latter on atmospheric processes, particularly the production of methane, carbon dioxide, and carbon monoxide, is considered.
    Keywords: GEOPHYSICS
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