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Volume 32, Issue 1
Displaying 1-7 of 7 articles from this issue
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Etsuo Uchida, Masahiro Naito, Shunnosuke Ueda1998 Volume 32 Issue 1 Pages 1-9
Published: February 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSAqueous speciation of zinc in 2N chloride solution was determined experimentally at 500 to 700°C and 0.5 to 1.0 kb by monitoring the effect of NaCl on ion exchange equilibria in the system CaTiO3-ZnTiO3-CaCl2-ZnCl2-H2O. The Ca/(Ca + Zn) value of the 2N aqueous chloride solution in equilibrium with both CaTiO3 and ZnTiO3 decreased with the increase of NaCl under all experimental conditions. This is due to the formation of tri-chloro zinc complex. The formation constant of tri-chloro zinc complex was estimated to be 1.1, 2.1 and 2.7 at 500, 600 and 700°C, 1 kb, respectively, and 2.6 at 600°C, 0.5 kb in logarithm. The formation constant of tri-chloro zinc complex increases with increasing temperature and decreasing pressure. This suggests that zinc can be effectively leached from rocks and magmas under higher temperature and lower pressure conditions.View full abstractDownload PDF (2238K) -
Che Abd. Rahim Mohamed, Shizuo Tsunogai1998 Volume 32 Issue 1 Pages 11-20
Published: February 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSSediment cores were obtained at six stations in the area across the northern Japan Trench including hemipelagic and oceanic basin zones, and analyzed for 231Pa as well as 230Th. The concentration of 231Pa in the surface sediments increased with both the distance from the coast and the increasing water depth in the slope and the trench zones except the oceanic basin. The vertical profiles varied widely from station to station, but they showed no distinct vertical trend at each station. Although the sedimentation rate of unsupported 231Pa was more strongly controlled by the accumulation rate of bulk sediments than by its concentration, its sedimentation rates were about 200 times larger in the continental slope and the trench zones than in the oceanic basin. Furthermore, the ratios of 231Pa/230Th decreased offshore. The boundary scavenging, therefore, is more pronounced for the removal of 231Pa from the water column. The activity ratios of 231Pa/230Th in the continental slope sediments were considerably greater than the production ratio in the water column of 0.092, and also remarkably larger in the western North Pacific than in the eastern North Pacific. The difference is probably due to biogenic opal, of which fraction is larger in the settling particles in the western North Pacific.View full abstractDownload PDF (2398K) -
C. T. Herzig, D. L. Kimbrough, Y. Tainosho, H. Kagami, S. Iizumi, Y. H ...1998 Volume 32 Issue 1 Pages 21-31
Published: February 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSRyoke granitoids on Ikoma-yama and Katsuragi-yama in the Kinki District, and on Yashiro-jima in the Yanai District, have Late Cretaceous zircon U/Pb isotopic crystallization ages. Older and Younger granites on Ikoma-yama were emplaced within a short time interval between 81 and 82 ± 1 Ma. Younger Ryoke granite on Katsuragi-yama, located south of Ikoma-yama, crystallized at 75 ± 3 Ma. The Gamano granodiorite and Kita-Oshima granite-gneiss on Yashiro-jima have overlapping crystallization ages of 95 to 96 ± 1 Ma. This result supports earlier ideas that the Gamano and Kita-Oshima rocks are cogenetic. An inherited component of Precambrian (1855 to 1953 Ma) radiogenic lead is present in some of the zircons from the Ryoke granitoids analyzed in this study. This result implies that older continental materials were assimilated into the granitic magmas. Possible sources include Precambrian basement or younger upper crustal rocks that contain recycled Precambrian detritus.View full abstractDownload PDF (3094K) -
Isoji Miyagi, Osamu Matsubaya, Satoru Nakashima1998 Volume 32 Issue 1 Pages 33-48
Published: February 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThe hydrogen isotopic composition of hornblende in volcanic rocks has potential to indicate processes such as degassing of a magma reservoir, as well as the origin of magmatic water. However, during eruption and high-temperature interaction with air, the isotope composition of hornblende can be altered. In order to establish criteria to select natural hornblende that preserves magmatic hydrogen isotopic ratios, hydrogen isotopic composition (δD), water contents, and colors of hornblendes were measured. A series of heating experiments on natural green hornblendes was conducted in air and under vacuum up to 1000°C. There observed a negative relationship between the intensity of redness (a∗) and water content among heated hornblendes in air and under vacuum, as well as natural samples from several Quaternary volcanos in Japan. Heating hornblende results in a significant increase in δD value that can be explained by a Rayleigh distillation (simultaneous degassing without hydrogen isotopic exchange between the gas and the mineral) model involving degassing of both H2O and H2. According to the model, maximum fractionation occurs when hornblende dehydrates only by H2 degassing. Application of the model indicates that hornblendes in pumice fragments from Plinian eruptions are most representative of the δD of pre-eruptive magma. In contrast, the δD values of minerals from lava flows, lava domes, or even from thick pumice flow deposits may have suffered from 1) hydrogen isotopic fractionation by mineral dehydration, and/or 2) isotopic re-equilibration with degassing magma during eruption stage and during cooling stage after the emplacement.View full abstractDownload PDF (3931K) -
Masafumi Sudo, Kozo Uto, Ken Anno, Osamu Ishizuka, Shigeru Uchiumi1998 Volume 32 Issue 1 Pages 49-58
Published: February 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSA new mineral standard for K-Ar dating, SORI93 biotite, has been prepared from the Sori Granodiorite in Gunma Prefecture, Japan. This is intended as a substitute of the existing standard, SORI biotite, which is well calibrated against international standards. The K2O and radiogenic 40Ar contents for SORI93 biotite have been determined to be 8.16 ± 0.04 (1σ) wt % and (25.0 ± 0.1) × 10-6 (1σ) cm3STP/g, respectively. The calculated K-Ar age is 92.6 ± 0.6 Ma, which is about 1 million years older than that of SORI biotite. Chloritization up to 10% partly occur along cleavages of SORI93 biotite. In order to certify the homogeneity, K2O contents have been repeatedly analyzed for 100, 50, 20 and 10 mg aliquots. The analytical result of 100 mg SORI93 biotite shows a relative standard deviation similar to that of SORI biotite and the geochemical standards, JG-1 and JB-1. The standard deviations of aliquots less than 100 mg are about twice those of the three standards. This inhomogeneity may be caused by the presence of partially chloritized biotite. It is suggested to use 100 mg to ensure the homogeneity of subsamples.View full abstractDownload PDF (2599K) -
Chitoshi Mizota, Kevin Faure, Katsuhiro Nakayama, Nanshi Zeng1998 Volume 32 Issue 1 Pages 59-63
Published: February 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSLarge boulder-size euhedral quartz crystals occur in the basal horizons of the Late Miocene Seto Porcelain Clay Formation, central Japan. The quartz crystals consist of smoky basal portion overgrown by translucent to milky white quartz. δ18O values (-1.5 to -0.2‰, SMOW) of the translucent to milky white quartz are considerably lower than the values of smoky quartz (+10.3 to +10.5‰). The oxygen isotope ratios of quartz and homogenization temperatures of fluid inclusions indicate that the translucent to milky white quartz overgrowths precipitated onto the early-stage smoky quartz in druses of the Naegi and/or Toki granites, from meteoric water dominant thermal waters that infiltrated into the granites during the latest stage of granitic activity in the late Cretaceous age.View full abstractDownload PDF (987K) -
R. Ramesh, R. V. Krishnamurthy1998 Volume 32 Issue 1 Pages 65-69
Published: February 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThe stable carbon isotope ratio (δ13C) of organic matter from the deep sea sediments shows an increase of 1 to 2‰ during glacial periods relative to inter glacial periods (Muller et al., 1983; Fontugne and Duplessy, 1986; Sackett, 1986; Sarkar et al., 1993). This has been variously explained as due to (1) change in the relative mixing proportions of the marine (δ13C = -20‰) and terrestrial (δ13C = -26‰) organic matter; (2) reduction in the pCO2 of the surface oceans accompanying that in the atmosphere (Rau et al., 1991) and (3) change in the oxic/anoxic conditions in the deep sea environment induced by changes in the surface ocean productivity. While these interpretations may have some merit, we suggest an alternative possibility, viz., a reduced availability of dissolved CO2 in the surface ocean for photosynthesis during glacial times due to (a) a reduction in the atmospheric CO2 concentration (Barnola et al., 1987) and (b) enhanced rates of photosynthesis due to a more vigorous atmospheric circulation in some regions (e.g., Pacific, Pedersen, 1983) or (c) reduced rates of air-sea exchange of CO2 due to the failure of monsoons in the northern Indian Ocean (Duplessy, 1982; Prell, 1984; Sarkar et al., 1990; Krishnamurthy, 1990). These would result in an increased use of dissolved bicarbonate (Hayes, 1993)-enriched in 13C by 9‰ relative to dissolved CO2, thereby enriching the glacial organic matter in 13C and causing an increase in oceanic pH. Using data reported for the northern Indian Ocean, we calculate such pH changes to be in the range of 0.01 to 0.13, consistent with recent estimates based on boron isotope analysis (Sanyal et al., 1995).View full abstractDownload PDF (1174K)
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