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Volume 24 (1990)
- Issue 6 Pages 349-
- Issue 5 Pages 309-
- Issue 4 Pages 193-
- Issue 3 Pages 123-
- Issue 2 Pages 47-
- Issue 1 Pages 1-
Volume 24, Issue 6
Displaying 1-5 of 5 articles from this issue
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Hodaka Kawahata, Steven D. Scott1990 Volume 24 Issue 6 Pages 349-356
Published: 1990
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSSulfide precipitation took place within pillow lavas in the Agrokipia ‘B’ deposit of the Troodos ophiolite, Cyprus. Such a deposit would have been originally expressed on the seafloor by the emergence of warm fluids in a situation comparable to that described at the Galapagos Spreading Center. Holes CY2A and CY4 by the International Crustal Research Drilling Group (ICRDG) provide an opportunity to study water-rock interaction in pillow lavas and the sheeted dike complex below the ancient seafloor. Sr-Rb isotope analysis as well as heat energy constraints yield an age of about 90 Ma. for the formation of the Agrokipia ‘B’ deposit and requires that the related hydrothermal alteration occurred on or close to a spreading axis. A narrow range of the 87Sr/86Sr ratios (0.70614-0.70660, av. 0.70633) of the hydrothermal solutions in the stockwork zone and underlying basement indicates that off-axis seafloor metamorphism and/or any alteration during obduction of the ophiolite were not accompanied by extensive metasomatism. The seawater/rock ratio of the completely hydrothermally altered rocks and the related hydrothermal solution in the stockwork zone and underlying basement was 12, which is unusually high compared with water/rock ratios from present seafloor hot springs (1 to 5). On the other hand, the end-member hydrothermal solution which entered the stockwork zone had an 87Sr/86Sr ratio of 0.70541 and a water/rock ratio of 5. Thus local, secondary circulation systems are required to explain the strontium isotopes and water/rock data, and probably are necessary for the formation of the subseafloor ore deposits.View full abstractDownload PDF (2244K) -
Hiroaki Sato, Shigeo Aramaki, Minoru Kusakabe, Jun-ichi Hirabayashi, Y ...1990 Volume 24 Issue 6 Pages 357-370
Published: 1990
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThe 1600 km long Cameroon volcanic line is composed of large polygenetic volcanoes and small monogenetic volcanoes. The latter conform monogenetic volcano groups consisting of small lava flows, cinder cones and maars. Chemical analyses on basalts from the central part of the Cameroon volcanic line showed that CaO contents of the basalts of polygenetic volcanoes are higher than those of monogenetic volcanoes, while the reverse relation is found for SiO2 contents. Incompatible trace elements are high in both basalts, but HFS/LIL ratios and La/Ba ratio are higher for polygenetic volcanoes than monogenetic volcanoes. Rb-Ba-La relations, representing the most incompatible elements for uni-, di- and tri-valent cations, indicate that basalts of polygenetic volcanoes are similar to depleted mid-oceanic ridge basalts, whereas, the basalts of monogenetic volcanoes are akin to continental flood basalts or oceanic island basalts. It is suggested that the major sources of the polygenetic volcanoes are the upwelling asthenosphere underneath the African plate, while those of the monogenetic volcanoes are the lowest portion of the subcontinental lithosphere.View full abstractDownload PDF (3529K) -
Neil E. Whitehead, John Barrie, Peter Rankin1990 Volume 24 Issue 6 Pages 371-378
Published: 1990
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSNiue Island, a raised coralline atoll in the South Pacific, has soils that have long been known to have strongly anomalous radioactivity. We now show that there is also a highly anomalous Hg content in the soils. It is associated with the radioactivity and the goethite/gibbsite content and the values are as high as those in soils over known Hg-mineralisation in volcanic settings, though no mineralisation is known on Niue and such an occurrence on this coral island would be geochemically unusual.View full abstractDownload PDF (1979K) -
Jun-ichi Matsuda, Takuya Matsumoto, Keisuke Nagao1990 Volume 24 Issue 6 Pages 379-382
Published: 1990
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSIn order to detect 3He produced by the cold nuclear fusion, we measured 3He in Ti electrode in an electrolytic cell containing deuterium. All the 3He amounts in the electrode were more or less in the same order of magnitude as that of hot blanks in the measurement by mass spectrometry. There was no difference in 3He amounts between the run products using H2O+LiH and D2O+LiD as electrolyte, and no correlation with the experimental time of electrolysis. The result indicates that the fusion rate of deuterons was less than 3×101/sec, much lower than the value (4×104) obtained by Fleischmann and Pons (1989). However, in our 3He measurement it was difficult to detect the fusion rate as low as 4×10-1 given by Jones et al. (1989). The obtained upper limit of the fusion rate suggests that the electrolytic refining is not the cause of high 3He/4He ratios observed in metals.View full abstractDownload PDF (1034K) -
1990 Volume 24 Issue 6 Pages e2
Published: 1990
Released on J-STAGE: February 06, 2009
JOURNAL FREE ACCESSDownload PDF (1900K)
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