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Volume 26 (1992)
- Issue 6 Pages 307-
- Issue 5 Pages 251-
- Issue 4 Pages 181-
- Issue 3 Pages 111-
- Issue 2 Pages 51-
- Issue 1 Pages 1-
Volume 26, Issue 2
Displaying 1-6 of 6 articles from this issue
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Pradeep Kumar, P. S. Goel1992 Volume 26 Issue 2 Pages 51-61
Published: April 20, 1992
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSIn residues of several iron meteorites, obtained by dissolution of a metal piece in 2M H2 SO4, isotopic ratio of 196Hg/202Hg has been measured by radiochemical neutron activation analysis in Hg fractions, released by stepwise heating. Both positive and negative deviations relative to terrestrial composition, have been found. Anomalies are more frequently observed in the high temperature fractions (200 < T < 600°C) as compared to the low temperature distillates (T ≤ 200°C). The largest deviations so far seen are, respectively, enrichment of 196Hg by 67% in a 400°C fraction of Carlton and depletion of the same isotope by 86% in a 300°C fraction of Sikhote Alin residue (magnetic) of <38 μm grain size. The anomalous components appear to be sporadic and heterogeneously distributed. A lack of homogenisation of the two isotopes that are produced in different nucleosynthetic processes suggests that iron meteorites have been formed in a non-magmatic process, entrapping presolar grains. Alternatively, some foreign materials presumably of different isotopic compositions might have been introduced in meteorite parent bodies during their collisions with other cosmic objects and or dense cloud of interstellar dust.View full abstractDownload PDF (2830K) -
Seiya Nagao, Hisashi Narita, Shizuo Tsunogai, Koh Harada, Toshiaki Ish ...1992 Volume 26 Issue 2 Pages 63-72
Published: April 20, 1992
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSPore waters in marine sediments from Funka Bay, Japan were squeezed with three squeezing methods and their U concentrations were measured. The pore water U squeezed with a multi-depth core squeezer without exposure to air is one order of magnitude less than the seawater U value. In contrast, the pore water U squeezed with a hydraulic squeezer under air and by a whole-core squeezer shows anomalously high values (maximum 53 μg/kg) even though care was taken to avoid air contact. The wide variation of pore water U from month to month is found for the hydraulic squeezing samples through a year. The difference in pore water U among three squeezing methods is considered to be due to oxidation artifacts during sample handling and squeezing. Oxidation of solid reduced U occurs rapidly on air contact, according to exposure experiments of anoxic sediment to air. The pore water U squeezed with the multi-depth core squeezer without oxidation artifacts decreases from the seawater U value at the surface to about 0.2–0.4 μg/kg at 3–10 cm depth in July, August, September and December 1990. These results suggest that pore water U in the Funka Bay sediments is removed to the sediments close to the sediment–water interface. This indicates removal of dissolved U from bottom seawater to sediment, but this cannot explain the enrichment of U in the solid phase below 40 cm depth. A more likely explanation for the discrepancy in vertical profiles between pore water and solid phase U is considered to be the change of deposition conditions between past and present.View full abstractDownload PDF (2981K) -
Tsutomu Sato, Hiroshi Wakita, Kenji Notsu, George Igarashi1992 Volume 26 Issue 2 Pages 73-83
Published: April 20, 1992
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSGeochemical and hydrological observations have been carried out at two hot spring wells in Ito City since July 1989. Anomalous changes in water level, temperature and chemical composition were observed during the 1989 seismic and volcanic events off the east coast of the Izu Peninsula: a water level rise of more than 2 m, a temperature rise of about 1°C and an increase of the SO42-/Cl- ratio by about 5%. Coseismic changes in these parameters were observed for two nearby earthquakes that occurred during the observation period, on February 20, 1990 (M = 6.5), and on August 5, 1990 (M = 5.1), supporting that these wells are very sensitive to earthquake occurrence. Relation between amplitude of coseismic change, magnitude and hypocentral distance indicates that the anomalous changes observed during the 1989 events were too large to be caused by the seismic events only. It is likely that magma movements associated with the seismic and volcanic events had a close connection with the geochemical and hydrological anomalies observed during the 1989 events. Major part of the significant anomalies including self-spouting observed in Ito City are interpreted to be possible precursors of the 1989 submarine volcanic eruption.View full abstractDownload PDF (2875K) -
Ken Shibata, Kazuhito Ozawa1992 Volume 26 Issue 2 Pages 85-97
Published: April 20, 1992
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSSm-Nd, Rb-Sr and K-Ar geochronological and isotopic analyses were made on the Hayachine-Miyamori arc ophiolite in the Kitakami Mountains, Northeast Japan. The Sm-Nd isochron for four whole-rock samples gives an age of 510 ± 70 Ma and an initial 143Nd/144Nd ratio of 0.51229 ± 0.00010 (εNd = +6.4 ± 2.0). The initial εNd for individual rocks ranges from +6.3 to +7.0, and is lower than that of the MORB. The age of 510 Ma is interpreted to represent the crystallization age of the Hayachine-Miyamori ophiolite. K-Ar ages of eight hornblendes range from 244 to 473 Ma, within which ages younger than about 400 Ma are thought to be affected by Cretaceous granitic intrusions. The K-Ar hornblende ages may indicate the times of tectonic emplacement to shallower levels. The initial 87Sr/86Sr ratios of eight whole rock samples from the Hayachine-Miyamori complexes show a wide variation: ranging from –4.0 to +31.9 as εSr. The nearly constant εNd and variable εSr suggest various extent of seawater alteration for these samples. Amphibolites whose protolith may be extrusive or shallow intrusive rocks give higher εSr than plutonic rocks, which is consistent with circulation of sea water during the metamorphism. However, coarse-grained gabbro intruded into host peridotites still have higher εSr than the MORB. The lower εNd and higher εSr for these gabbroic rocks, which occur in the host peridotites with arc-related geochemical characteristics, suggest that these isotopic signatures were recorded within an arc upper mantle. This mantle signature may be explained by an involvement of radiogenic fluid or melt derived from subducting slab, which had been altered by sea water at a mid-ocean ridge.View full abstractDownload PDF (4151K) -
Kaori Suzuki, Hikaru Kouta, Hiroshi Nagasawa1992 Volume 26 Issue 2 Pages 99-104
Published: April 20, 1992
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSInterdiffusivity of Hf and Zr in the zircon (ZrSiO4)-hafnon (HfSiO4) solid solution system was measured by (1) coupled annealing of synthetic hafnon and natural zircon and (2) heating of zircon crystal with a layer of hafnon epitaxially grown over the surface of zircon crystal. Because of the unexpectedly low diffusivity of Hf-Zr pair, practically usable value of diffusion coefficient was not obtained by the conventional coupled annealing technique. By use of the sample prepared by an epitaxial over-growth technique the upper limit of diffusion coefficient for Hf-Zr interdiffusion in the zircon-hafnon system was found to be ≤1 × 10-15 cm2·sec-1 at 1600°C. The observed low diffusivity of Hf-Zr pair in the zircon-hafnon system implies that diffusion of U, Th and radiogenic daughters does not affect Io age of zircon significantly during its residence in the parental magma, assuming that the diffusivities of those elements do not differ significantly from that observed for Hf-Zr.View full abstractDownload PDF (1804K) -
Yoji Arakawa1992 Volume 26 Issue 2 Pages 105-109
Published: April 20, 1992
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThe 143Nd/144Nd ratios were determined for twelve GSJ (Geological Survey of Japan) rock reference samples. The results are summarized in Table 1. Analytical uncertainties in 143Nd/144Nd ratios of several separate measurements are slightly larger for granite standard samples (JG-1, JG-1a) than for basalt (JB-1) and andesite (JA-1) samples. This is possibly due to incomplete sample decomposition and Nd separation, or to inhomogeneity in modal composition, hence chemical composition of the powdered samples.View full abstractDownload PDF (1250K)
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