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  • LUNAR AND PLANETARY EXPLORATION  (7)
  • GEOPHYSICS  (6)
  • 1
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    Three-dimensional instabilities of mantle convection with multiple phase transitions (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The effects of multiple phase transitions on mantle convection are investigated by numerical simulations that are based on three-dimensional models. These simulations show that cold sheets of mantle material collide at junctions, merge, and form a strong downflow that is stopped temporarily by the transition zone. The accumulated cold material gives rise to a strong gravitational instability that causes the cold mass to sink rapidly into the lower mantle. This process promotes a massive exchange between the lower and upper mantles and triggers a global instability in the adjacent plume system. This mechanism may be cyclic in nature and may be linked to the generation of superplumes.
    Keywords: GEOPHYSICS
    Type: Science (ISSN 0036-8075); 259; 5099; p. 1308-1311.
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  • 2
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    Development of diapiric structures in the upper mantle due to phase transitions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Solid-state phase transition in time-dependent mantle convection can induce diapiric flows in the upper mantle. When a deep mantle plume rises toward phase boundaries in the upper mantle, the changes in the local thermal buoyancy, local heat capacity, and latent heat associated with the phase change at a depth of 670 kilometers tend to pinch off the plume head from the feeding stem and form a diapir. This mechanism may explain episodic hot spot volcanism. The nature of the multiple phase boundaries at the boundary between the upper and lower mantle may control the fate of deep mantle plumes, allowing hot plumes to go through and retarding the tepid ones.
    Keywords: GEOPHYSICS
    Type: Science (ISSN 0036-8075); 252; 1836-183
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  • 3
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    Measurements of concentrations of chlorofluoromethanes (CFMs) carbon dioxide and carbon isotope ratio in stratospheric and tropospheric air by grab-sampling systems (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Measurements of concentrations of chlorofluoromethanes (CFMs), carbon dioxide and carbon isotope ratio in stratospheric and tropospheric air by grab-sampling systems are reported. The balloon-borne grab-sampling system has been launched from Sanriku Balloon Center three times since 1981. It consists of: (1) six sampling cylinders, (2) eight motor driven values, (3) control and monitor circuits, and (4) pressurized housing. Particular consideration is paid to the problem of contamination. Strict requirements are placed on the choice of materials and components, construction methods, cleaning techniques, vacuum integrity, and sampling procedures. An aluminum pressurized housing and a 4-m long inlet line are employed to prevent the sampling air from contamination by outgassing of sampling and control devices. The sampling is performed during the descent of the system. Vertical profiles of mixing ratios of CF2Cl2, CFCl3 and CH4 are given. Mixing ratios of CF2Cl2 and CFCl3 in the stratosphere do not show the discernible effect of the increase of those in the ground level background, and decrease with altitude. Decreasing rate of CFCl3 is larger than that of CF2Cl2. CH4 mixing ratio, on the other hand, shows diffusive equilibrium, as the photodissociation cross section of CH4 is small and concentrations of OH radical and 0(sup I D) are low.
    Keywords: GEOPHYSICS
    Type: International Council of Scientific Unions Handbook for MAP, Vol. 18; 7 p
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  • 4
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    Solar helium and neon in the Earth (1994)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Neon isotopic compositions in mantle-derived samples commonly are enriched in (20)Ne and (21)Ne relative to (22)Ne compared with atmospheric neon ((20)Ne/(22)Ne and (21)Ne/(22)Ne ratios in atmospheric neon are 9.8 and 0.029, respectively), together with significant primordial (3)He. Such results have been obtained on MORB's, intraplate plume-related oceanic island basalts, backarc basin basalts, mantle xenoliths, ancient diamonds and CO2 well gases (e.g., 1 - 8). The highest (20)Ne/(22)Ne ratio observed in MORB glasses (= 13.6 plus or minus 1.3 is close to the solar value (= 13.6, as observed in solar wind). In order to explain the enrichment of (20)Ne and (21)Ne relative to atmospheric neon for samples derived from the mantle, it is necessary to postulate the presence of at least two distinct non-atmospheric components. The two most likely candidates are solar and nucleogenic ((20)Ne/(22)Ne solar = 13.6 (21)Ne/(22)Ne solar = 0.032, (20)Ne/(22)Ne nucleogenic = 2.5 and (21)Ne/(22)Ne nucleogenic = 32). This is because solar neon is the only known component with a (20)Ne/(22)Ne ratio greater than both the atmospheric value and that observed in samples derived from the mantle. Nucleogenic neon is well known to elevate (21)Ne/(22)Ne ratios. Neon isotopic signatures observed in mantle-derived samples can be accounted for by mixing of the three neon end members: solar, nucleogenic and atmospheric.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., Conference on Deep Earth and Planetary Volatiles; p 16
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  • 5
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    Xe-129 - Xe-128 and Ar-40 - Ar-39 chronology of two Antarctic enstatite meteorites (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Xe-129 - Xe-128 and Ar-40 - Ar-39 analyses has been performed on two Antarctic enstatite meteorites, the chondrite Y-691 and the aubrite (enstatite achondrite) ALH-78113. Both meteorites have complex Ar-40 - Ar-39 release patterns to which no unambiguous age assignment is possible. Both give apparently satisfactory Xe-129 - Xe-128 correlations corresponding to unusual ages. The I-Xe age of the chondrite Y-691 is 16 Ma after Bjurbole, not unusual for chondrites in general but 10 Ma later than previously known ages for enstatite chondrites. The I-Xe age of the aubrite ALH-78113 is 210 Ma after Bjurbole, the latest age (rather than a limit) so far observed by the I-Xe technique, but this age assignment must be considered tentative because of the possibility that it is significantly influenced by terrestrial I contamination.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: National Institute of Polar Research, Memoirs, Special Issue (ISSN 0386-0744); 30 D; 275-291
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  • 6
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    The atmospheric inventory of Xenon and noble cases in shales The plastic bag experiment (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A novel trapped gas analysis protocol is applied to five shales in which the samples are sealed in air to eliminate the possibility of gas loss in the preanalysis laboratory vacuum exposure of a conventional protocol. The test is aimed at a determination concerning the hypothesis that atmospheric noble gases occur in the same proportion as planetary gases in meteorites, and that the factor-of-23 deficiency of air Xe relative to planetary Xe is made up by Xe stored in shales or other sedimentary rocks. The results obtained do not support the shale hypothesis.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 4597-461
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  • 7
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    Measurements of I-129 in meteorites and lunar rock by tandem accelerator mass spectrometry (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Precise measurements of the half-life of I-129 in three different meteorites and one lunar surface rock are reported. The meteorite source of I-129 was produced by cosmic ray secondary neutron reactions on Te, while the source in lunar materials in spallation on barium and rare earth elements. The Abee, Allende, and Dhajala meteorites were examined, together with the lunar rock 14310. Details of the process used to extract the iodine are provided. The Abee and Allende samples exhibited a production of 0.5 atom/min per gm of Te from the (n,2n) reaction and 0.05 atom/min/gm for the (n,gamma) reaction. The I-129 is concluded to be a viable tool for long-lived cosmogenic nuclide studies. Further work to extend the data to include the constancy of the cosmic ray flux, the meteorite bombardment history, and the cosmic exposure age dating by means of the I-129 and Xe-129 method is indicated.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 305; 611
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  • 8
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    Depth profiles of Mn-53 in lunar rocks and soils (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Results of measurements of cosmic-ray-produced Mn-53 taken down the length of the Apollo 16 deep drill core are presented. They indicate that the lunar regolith has been unmixed, on a meter scale, for the past 5 million years at the location of this core. The data are in agreement with earlier Mn-53 measurements on the Apollo 15 drill core. Mn-53 activity profiles in 14310, 12002, and 14321 are compared to each other; all three rocks have probably been on the lunar surface long enough to saturate their solar cosmic-ray-produced Mn-53 (half-life = 3.7 m.y.) activity.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Science Conference; Mar 18, 1974 - Mar 22, 1974; Houston, TX
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  • 9
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    Adsorption and excess fission Xe - Adsorption of Xe on vacuum crushed minerals (1982)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: It is hypothesized that adsorption is not likely to provide a sufficiently precise mechanism for the concentration of excess fission Xe in the entire lunar regolith, in view of laboratory analogs of the lunar soil and calculations of the residence times of noble gases in the present day regolith. Lunar cold trap and episodic degassing models are difficult to reconcile, however, with the generality of excess fission Xe in all gas-rich highland breccias. It is concluded that the high Xe concentration in such highland breccias is not the result of Xe adsorption prior to the trapping of this component.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 15, 1982 - Mar 19, 1982; Houston, TX
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  • 10
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    Mn-53 in the Apollo 15 and 16 drill stems - Evidence for surface mixing (1976)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The activity of cosmic ray produced Mn-53 has been measured in a series of samples from the upper 10 cm of the Apollo 15 and 16 drill stems. The activity profiles for both cores indicate disturbance to depths of about 3 g/sq cm within the last 6 m.y. In at least one case (Apollo 16) the soil has been gardened to at least 14 g/sq cm within the last 10 m.y., and material from the upper less than 2 g/sq cm has been buried to 14 g/sq cm by this gardening. The results for the Apollo 15 core are compatible with a wide variety of possible histories including loss or gain of material.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Science Conference; Mar 15, 1976 - Mar 19, 1976; Houston, TX
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