GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
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Volume 9, Issue 4
Displaying 1-8 of 8 articles from this issue
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  • Chemical aspects of viscous flow in planetary mantles
    Robert F. Mueller
    1975 Volume 9 Issue 4 Pages 185-199
    Published: December 20, 1975
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.9.185
    JOURNAL FREE ACCESS
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    A critique is presented of the various mathematical rheological models, and their applications to the mantles of the Earth and the terrestrial planets is discussed. One of the models considered is derived from absolute reaction rate theory of chemical kinetics and allows for automatic transition between Newtonian (strain rate proportional to stress) and non-Newtonian viscous flow depending on the differential stress and the strain rate. A good fit to data is obtained when this model is applied to the post glacial Fennoscandian uplift. The deduced strain rate, as obtained from the assumption of proportionality between strain rate and rate of uplift, is in the range of 10-16 to 10-15sec-1, while the deduced viscosities fall in the range of 1022 and 1023 poises with uncertainties of an order of magnitude. Flow is found to be non-Newtonian but is becoming increasingly Newtonian with time. The various thermodynamic parameters of viscous flow, including pressure and temperature sensitivity, are also discussed and the viscous relaxation times of the different terrestrial planets are compared in terms of their temperatures. From this analysis it is concluded that the relatively low relief and the recently discovered circular depressions on Venus are probably a result of high lithospheric temperatures on this planet. The depressions are probably due to subsidence around basic volcanic centers and correspond to shield volcanos on Earth and Mars. Application of the same theory to terrestrial global plate tectonics leads to the conclusion that there should be viscous accretion of mantle material on the postulated cool descending slab of oceanic crust and that the viscosity of planetary mantles should be increasing with time.
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  • Significance of Cs/Rb ratios in volcanic rocks as exemplified by the Nohi Rhyolite complex, Central Japan
    Kenji Okamoto, Susumu Nohda, Yasuyuki Masuda, Takashi Matsumoto
    1975 Volume 9 Issue 4 Pages 201-210
    Published: December 20, 1975
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.9.201
    JOURNAL FREE ACCESS
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    Cs/Rb ratio was examined on the Nohi rhyolite complex in Central Japan, which is composed mainly of rhyolitic ignimbrite. The variation in the Cs/Rb ratio of the magma through crystallization differentiation was estimated using a Rayleigh fractionation model and available distribution coefficients between phenocryst minerals and co-existing groundmass. It was found that the K/Rb ratio of this complex decreased from 273 to 125, but the Cs/Rb ratio remained constant through the differentiation process. The initial Cs/Rb ratio of this magma is 0.030 ± 0.005. The value is very close to the average Cs/Rb ratio of the ignimbrite in the Taupo region, Northern New Zealand, but is distinctly heigher than that of ocean floor basalts. To estimate the effect of contamination the Rb-Sr whole rock isochron method was used.
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  • A metamorphogenic alteration zone around the stratiform Broken Hill ore deposits, Australia
    I. R. Plimer
    1975 Volume 9 Issue 4 Pages 211-220
    Published: December 20, 1975
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.9.211
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    A symmetrical metamorphic alteration zone around the Broken Hill orebodies derives from retrogressive metamorphism. This zone is at least 300m wide and is characterized by a great increase in Rb/Sr and the replacement of earlier high grade metamorphic minerals by sericite. The alteration observed probably results from fluid ascent along permeable sulphide-silicate competency boundaries at the waning stages of granulite facies metamorphism.
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  • Radioactive disequilibrium of thorium series nuclides in hot spring deposits
    Takashi Okubo, Masanobu Sakanoue
    1975 Volume 9 Issue 4 Pages 221-226
    Published: December 20, 1975
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.9.221
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    The concentrations of radium isotopes (226Ra and 228Ra) and thorium isotopes (232Th, 230Th and 228Th) in a calcium carbonate sinter cone and hokutolites were determined. These nuclides were analyzed either by non-destructive γ-ray spectrometry or by α-ray sepctrometry after radiochemical separation. The concentrations of 232Th, 228Ra and 228Th (thorium series nuclides) in a sinter cone were 2.4 × 10-2, 4.3 × 10-1 and 7.1 × 10-1 dpm/g, respectively. It was confirmed that thorium series nuclides in this sample were not in radioactive equilibrium with their parent, 232Th. Hokutolite samples collected recently showed higher radioactivities of 228Ra, ranging from 9.6 × 104 to 2.8 × 104dpm/g BaSO4. These values give a rate of deposition and an initial composition of the radionuclides in the hokutolite.
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  • Rocks with negative cerium anomalies, dredged from Shatsky Rise
    Akimasa Masuda, Shigeru Nagasawa
    1975 Volume 9 Issue 4 Pages 227-233
    Published: December 20, 1975
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.9.227
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    Some of basaltic rocks dredged from Shatsky Rise have large negative cerium anomalies. Also these samples have a wide variation in manganese content, and there appears to be some relationship between the extent of cerium anomaly and the manganese content. These observations may be of much significance for discussions of manganese nodule genesis.
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  • Ultimate origin of “ore solutions”: Ocean water?
    Yoshimichi Kajiwara
    1975 Volume 9 Issue 4 Pages 235-239
    Published: December 20, 1975
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.9.235
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    Available thermochemical data suggest that the present-day ocean waters have a great potentiality of ore deposition in a comparatively wide range of such hydrothermal conditions as might generally be encountered within the earth's crust environments. It appears probable that a majority of hydrothermal metalliferous ores in nature are the essential products of incorporated ocean waters heated and reduced in the earth's crust during processes of orogeny. It is also suggested that the ocean waters are linked with hydrothermal solutions in the earth's crust to form a single cyclic geochemical system and that the abundances of ore-forming elements in the oceans are indirectly being controlled by the solubility limits of common ore minerals existing in the uppermost earth's crust.
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  • Comments on paper by P. K. Kuroda ‘The puzzle of the rare gases and of oxygen in materials within the solar system’
    Robert N. Clayton
    1975 Volume 9 Issue 4 Pages 241
    Published: December 20, 1975
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.9.241
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    P. K. Kuroda
    1975 Volume 9 Issue 4 Pages 242
    Published: December 20, 1975
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.9.242
    JOURNAL FREE ACCESS
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