GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
26 巻 , 5 号
選択された号の論文の5件中1~5を表示しています
  • Jun-ichi Matsuda, Tatsuo Maekawa
    1992 年 26 巻 5 号 p. 251-259
    発行日: 1992年
    公開日: 2008/04/08
    ジャーナル フリー
    We have examined the elemental abundances of noble gases in graphite and diamond exposed to a glow discharge in a mixed noble gas atmosphere. The heavier noble gases were much enriched both in the diamond and the graphite compared to samples merely exposed to ambient gases without discharge. The noble gases were released below 800°C for all graphite samples, regardless of the applied voltage. Considerable amounts of heavy noble gases were released at higher temperatures from the diamonds exposed to higher voltages, suggesting that noble gases were more tightly implanted into the diamond than into the graphite. These results are relevant to the origin of noble gases in ureilite if carbon materials were of vapor growth origin in the solar nebula. Noble gases could have been contained in the diamond but not in the graphite, because of the higher retentivity of noble gases in diamonds at their formation temperatures.
  • Shigeko Togashi, Tsuyoshi Tanaka, Takeyoshi Yoshida, Ken-ichi Ishikawa ...
    1992 年 26 巻 5 号 p. 261-277
    発行日: 1992年
    公開日: 2008/04/08
    ジャーナル フリー
    On the basis of trace element abundances and Sr and Nd isotope ratios, Quaternary island arc low-alkali tholeiites (IAT) in Northeast Japan are divided into two types; U (undepleted)- and D (depleted)-IAT. U-IAT are characterized by high and constant abundances of Large Ion Lithophile Elements (LILE), which are 10–20 times higher than the primitive mantle value. The range of Nd isotope ratios of U-IAT is identical within errors to the Bulk Earth value. The 87Sr/86Sr ratios of U-IAT range from 0.7047 to 0.7057, greater than or equal to the currently accepted Bulk Earth value, and these variations can be caused by initial heterogeneity in Rb/Sr ratios of the primitive mantle. It is argued that U-IAT magmas were derived by 5–10% batch partial melting of the primitive mantle. D-IAT are characterized by convex-upward patterns with a maximum normalized value for an alkaline earth element in a primitive mantle versus ionic radii (NPR) abundance diagram. The degree of depletion in the elements with larger ionic radii is greater than those with smaller ones. These characteristics cannot be explained by magma compositional variations derived by different degrees of partial melting of a homogeneous mantle or by fractional crystallization. They can rather be explained by a variation in the composition of a previously depleted mantle source. The isotopic compositions of Sr and Nd range from the value of the Bulk Earth to that of the most depleted oceanic island basalt, and are well correlated with Nb/Y ratios. A mantle isochron of about 1 Ga is obtained for Nd and Sm isotopes. D-IAT magmas are considered to have formed in two stages consisting of depletion in LILE and Nb due to a loss of an extremely small amount of melt (<1%), about 1 Ga from a primitive mantle, and more recently followed by 5–10% partial melting episode under the conditions of formations typical of the U-IAT magmas.
  • Toshimori Sekine, Shigeo Aramaki
    1992 年 26 巻 5 号 p. 279-290
    発行日: 1992年
    公開日: 2008/04/08
    ジャーナル フリー
    Near-liquidus relations in one-atomsphere dry and water saturated high pressure conditions were experimentally determined on a pumice erupted from Usu volcano, Hokkaido, on August 14, 1977, at temperatures of 890°C to 1220°C, up to 1400 bar, and at a fixed oxygen fugacity (fO2) close to the Ni-NiO buffer. Plagioclase was the liquidus phase and accompanied with the subsequent phase of orthopyroxene up to 1400 bar. The temperature difference betweeen the plagioclase and orthopyroxene liquidi decreases with increasing water pressure, and an extraporation showed a crossing at about 900°C and 1500 bar. This temperature and water pressure may approximate the physical condition of the Usu magma containing both plagioclase and orthopyroxene as a small amount of phenocrysts shortly prior to eruption if the magma was saturated with H2O. Summarizing the experimentally-determined, H2O-saturated coprecipitation pressures and temperatures for the liquidus minerals from felsic magmas, so far reported in literature, a clear relationship is empirically derived for magmatic water pressure, temperature and the chemical composition of magmas. Using a compositional parameter such as the normative ratio of plagioclase to the sum of plagioclase plus pyroxene, the maximum water pressure and minimum temperature of magma immediately prior to eruption can be estimated graphically. This information may be useful to infer the physical conditions for historical activities of volcanoes vased on the mineralogical and petrochemical investigations.
  • Yuri A. Taran, Pavel V. Torokhov, Boris G. Pokrovsky, Irina Y. Shabaye ...
    1992 年 26 巻 5 号 p. 291-297
    発行日: 1992年
    公開日: 2008/04/08
    ジャーナル フリー
    Stable isotope ratios of C, S, and O have been measured on minerals associated with active hydrothermal vents, plus a free gas sample which was first found and collected from Piip submarine volcano, southern Bering Sea. The active vents were discovered during the 1990 expedition of the R/V “Akademik Mstislav Keldysh” using the deep submersible “MIR”. The free gas sample and a few fragments of anhydrite chimney and surrounding gypsum- and pyrite-bearing precipitates were collected from the high-temperature field of the North Peak of the volcano. The gas is methane-dominant (80.6%, C1/C2+ = 260). CH4 and CO2 carbon isotope ratios (−48.7‰ and −21.9‰, respectively), as well as the spectrum of C1–C4 hydrocarbons indicate a “thermogenic” origin of the gas. The δ34S values of anhydrite and gypsum (about of 22.5‰) from the northern field are typical for many modern seafloor hydrothermal systems. Pyrite-bearing altered rocks with δ34S = −2.4‰ were formed by recent hydrothermal activity of the volcano. Samples of massive calcite and fragments of aragonite chimneys (containing pyrite) were collected from the low-temperature South Peak field. Aragonite chimney material and massive calcite from the southern field with δ13C = −36 to −29‰ and δ18O = 19–21‰ were formed at about 60°C. Barite and pyrite recovered from the southern field were found to be significantly enriched in 34S (up to 39‰ and +9.2‰, respectively). These data indicate that the C and S isotope compositions of vent material from the southern field are controlled by reduction of marine sulfate by organic sediments or hydrocarbons.
  • Hiroshi Satake, Takayuki Yamane
    1992 年 26 巻 5 号 p. 299-305
    発行日: 1992年
    公開日: 2008/04/08
    ジャーナル フリー
    Monthly deposition rates of non-sea salt (nss-)sulfate from the atmosphere were observed at Toyama (1981–1991) and Wajima (1982–1984), both facing the Sea of Japan. The deposition rates at Toyama and Wajima showed similar seasonal variations with a large increase in winter, showing a good correlation to sodium deposition rate which is one of indicators of transport from the Sea of Japan. Thus, the increase in deposition rate in winter is attributed to the long-distance transport of sulfur dioxide from the Asian continent. The deposition rate and nss-SO4/Na ratio in each winter season during 1981–1991, however, did not show an increase with time, though the annual consumption rate of coal in East Asia increased by more than 50% in the 1980s. When the nss-sulfate deposition rate is plotted against the nss-calcium deposition rate, the deposition rates in the summer season shows a correlation of 1:1 in mole. This suggests that most of the nss-sulfate in summer is due to calcium sulfate emitted from flue gas desulfurization plants. On the contrary, in winter, the large increase in nss-sulfate was coupled with a slight increase in nss-calcium, but the ratio of nss-Ca/nss-SO4 was lower than unity. This suggests that nss-sulfate in winter can be a mixture with variable ratios of calcium sulfate in Japan to sulfuric acid converted from sulfur dioxide from the Asian continent.
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