巻号一覧
24 巻, 1 号
選択された号の論文の5件中1～5を表示しています
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Yoshiyuki Nozaki, Vimonrut Kasemsupaya, Hiroyuki Tsubota1990 年 24 巻 1 号 p. 1-6
発行日: 1990年
公開日: 2008/04/08
ジャーナル フリーNew data on 228Ra and 226Ra concentrations in the northern North Pacific are presented. Due to upwelling in the northern latitudes, 226Ra concentration is twice as much as that of the mid Pacific. The trend in the variation of surface 226Ra and dissolved SiO2 concentrations appears to be the same in the Pacific and the Atlantic oceans. A map of 228Ra/226Ra activity ratio in the surface water of the Pacific Ocean was constructed based on our data and those in the literature. The high 228Ra/226Ra activity ratio follows the prevailing surface currents such as the Kuroshio and the California Currents with low values at the center of the subarctic and the mid North Pacific gyres. The map is useful to identify the fluvial, coastal and shelf influences in the surface open ocean.抄録全体を表示PDF形式でダウンロード (1490K) -
Ichiro Kaneoka1990 年 24 巻 1 号 p. 7-19
発行日: 1990年
公開日: 2008/04/08
ジャーナル フリーBased on the radiometric age (mostly K-Ar and 40Ar-39Ar ages) and isotopic ratio data for volcanic rocks recovered from the Japan Sea floor, the formation age and the characteristics of magma sources for these volcanic rocks are discussed. Most volcanic rocks from the Yamato and Japan Basins, where oceanic crusts are presumed to exist, show radiometric ages of less than 20Ma. Igneous rocks dredged from such areas as continental remains are conjectured show radiometric ages of more than 100Ma. Volcanic activity in the Yamato Bank area along the borderland of the Yamato Basin seems to have ceased after 20Ma, which might have related to the formation of the Yamato Basin. Combining such data with the detailed information on the obtained ages, the formation of the Yamato Basin has been inferred to have started prior to 17Ma and not later than around 25Ma. The Japan Basin probably formed almost at the same period or slightly earlier. 87Sr/86Sr ratios for volcanic rocks are systematically different between the Yamato Basin and the Yamato Bank together with continental shelf areas: the former indicate values of 0.7035-0.7040, whereas the latter of higher than 0.7045. This might reflect the difference in the degree of incorporation of continental crustal materials.抄録全体を表示PDF形式でダウンロード (3720K) -
Yasuhiro Kiyosu, H. Roy Krouse1990 年 24 巻 1 号 p. 21-27
発行日: 1990年
公開日: 2008/04/08
ジャーナル フリーAbiogenic reduction of sulfate by acetic acid has been conducted at temperatures ranging from 241 to 340°C. The sulfides produced and the remaining sulfates have been chemically and isotopically quantified. The reaction of the aqueous sulfate reduction obey first-order kinetics. The rate constants are strongly dependent on temperature. The temperature dependence of the reaction rate (min-1) is given by the following rate law: log k=-10.3×103/T+15.1. The activation energy for the reaction of sulfate reduction is 208 kJ mol-1. The remaining sulfates display distinct sulfur isotopic variations under a closed system due to the kinetic isotope effect. The kinetic isotope fractionation factor can be expressed as: 103(α-1)=3.32×106/T2-4.19. The kinetic isotope effects during abiogenic reduction of the sulfate may depend on the atomic hydrogen produced, independent of the reducing agents.抄録全体を表示PDF形式でダウンロード (1681K) -
Yong-Fei Zheng1990 年 24 巻 1 号 p. 29-37
発行日: 1990年
公開日: 2008/04/08
ジャーナル フリーAs a continuum of the preceding studies on the three-dimensional U-Pb method (Zheng, 1989), a further U-Pb discordia plane model is developed by taking the measured isotope ratios 235U/207Pb, 206Pb/207Pb and 204Pb/207Pb for X, Y and Z axis respectively. Its geometry and applicability are elucidated in order to show the advantage of the three-dimensional U-Pb isotopic data presentation.抄録全体を表示PDF形式でダウンロード (2112K) -
Miho Tanaka, Hiroshi Shimizu, Akimasa Masuda1990 年 24 巻 1 号 p. 39-46
発行日: 1990年
公開日: 2008/04/08
ジャーナル フリーThe rare earth element (REE) abundances in twenty-one seawater samples around the Japanese Islands have been precisely determined by the isotope dilution method. Besides Ce anomaly, REE patterns of the seawater samples show a zigzag feature reflecting the lanthanide tetrad effect, which is considered to be associated with the filling of 4f electron orbitals. Particularly, the third and the fourth tetrads, zigzags in Gd-Dy-Er and Er-Yb-Lu spans, are clearly observed. Furthermore, most of the REE patterns shown here demonstrate a straight line for La-Nd-Sm-Eu and a discontinuity between Eu and Gd. The degree of the third tetrad effect becomes larger with the increase of the discontinuity between Eu and Gd.抄録全体を表示PDF形式でダウンロード (1741K)
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