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Volume 28, Issue 1
Displaying 1-5 of 5 articles from this issue
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Ichiro Kaneoka, Nobuo Takaoka, Sumio Miyashita, Hidekazu Tokuyama1994 Volume 28 Issue 1 Pages 1-9
Published: February 20, 1994
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESS40Ar-39Ar analyses were performed for two volcanic rocks recovered from the flank of the Okushiri Ridge, located at the northeastern part of the Japan Basin in the Japan Sea. A basalt (TB3-1), collected by a dredging gives a good plateau age of 14.2 ± 0.3 Ma, whereas a basaltic andesite (353-2a) recovered by a dive with the submersible SHINKAI 2000 gives a much older plateau age of 32.7 ± 0.6 Ma. The former age is similar to those obtained for some volcanic rocks from the seamounts in the Yamato Basin, but the latter is definitely older than those obtained for ODP samples. Since the latter sample was recovered with a subrounded surface, a possibility of exotic origin cannot be ruled out. Present results are not inconsistent with an inference that the Okushiri Ridge was formed during the Japan Sea evolution.View full abstractDownload PDF (2067K) -
Jie-Dong Yang, Xian-Cong Tao, Shi-Jin Xu, Zhong-Li Tang1994 Volume 28 Issue 1 Pages 11-18
Published: February 20, 1994
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSSm-Nd isotopic study for the ore-bearing Jinchuan ultramafic rocks in Gansu province, China, reveals the age of 1508 ± 31 Ma, which is obtained by Sm-Nd internal isochron method. The Rb-Sr isotopic system of the Jinchuan rocks have been contaminated by crustal materials, but little influence of crustal materials disturbed their Sm-Nd isotopic system. The determined results for acid-washed pyroxenes show that the source region of the Jinchuan ultramafic rocks may possess the following features: relatively homogeneous negative εNd(T) values, relatively dispersed εSr(T) values (generally larger than +60), and exhibiting a horizontal distribution in Nd-Sr correlation diagram.View full abstractDownload PDF (1647K) -
Iwao Kawabe, Tomoki Inoue, Seiji Kitamura1994 Volume 28 Issue 1 Pages 19-29
Published: February 20, 1994
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSICP-AES analyses of REE in two GSJ carbonate reference rocks of JDo-1 and JLs-1 have been made, and then compared with reported INAA results. Both of our ICP-AES and reported INAA results for JDo-1 are in reasonably good agreement, whereas most of the INAA analyses of Ce, Nd, Sm and Lu for JLs-1 are higher than our ICP-AES values by factors of 4 to 20. The contrasting results between JDo-1 and JLs-1 are related to their greatly different U/REE ratios: JLs-1 has 20–100 times higher U/REE ratios than JDo-1. The apparent disagreement in JLs-1 reveals the significance of fission and spectral interferences due to coexisting 235U and 238U in INAA determination of REE. We have estimated the fission interferences for 140La, 141Ce, 147Nd, and 153Sm from theoretical calculations. Our estimates agree reasonably with the reported experimental data for the fission interferences. The fission interference in 141Ce can explain the difference between INAA and ICP-AES data of Ce for JLs-1. The extent of fission interference in 147Nd is estimated. to be almost the same as that in 141Ce. Even the fission interference in 140La becomes significant, when samples with U/La ratio greater than unity are irradiated for 8–12 hours and then cooled for more than several days. This must be a reason for that most of INAA values for La in JLs-1 are about 50% higher than our ICP-AES value. Most of the INAA analyses of Sm and Lu for JLs-1 are biased to about ten times higher values by the γ-ray interferences of 239Np produced from 238U. Because of the great potential of fission and spectral interferences in INAA for geochemical samples with high U/REE ratios, we should be careful for their Ce anomalies and REE patterns based on such INAA data.View full abstractDownload PDF (2544K) -
Tadanori Arakaki, Yukiko Dokiya, Yukio Kodama, Jun-ichi Ohyama, Kan Og ...1994 Volume 28 Issue 1 Pages 31-46
Published: February 20, 1994
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSTwenty two samples of surface sediments were obtained by means of an Ekman Birge sampler during 1967–1989 in the East China Sea and the Yellow Sea area. Subsequent leaching with water, 6% acetic acid, 0.1 N HCl, and 30% H2O2 were done, followed by digestion with a mixture of mineral acids (HF, HNO3 and HClO4), in order to separate the chemical species, mainly of exchangeable ions, carbonate fraction, sulfide, organic metal fraction and mineral fraction. The concentrations of Ca, Mg, Sr, Ba, Cr, Ni, Mn, Fe, Al and Ti were determined for each fraction by multi-channel ICP emission spectrometry. The regional distribution of the total concentrations of the elements are summarized as follows: (i) Ca and Sr are higher at the edge of continental shelf, (ii) Mn, Ba and Cr are higher near the Changjiang mouth, and (iii) Mg, Al, Ti and Ni are relatively uniform. The behavior of alkaline earth elements in the acetic acid soluble fraction is explained by the contribution of carbonates to the sediments. High Mg/Ca ratios upto 3.5 in the hydrofluoric acid fraction of offshore sediments are ascribed to isomorphic ionic exchange of clay minerals.View full abstractDownload PDF (2849K) -
Bin Li, Oliver K. Manuel1994 Volume 28 Issue 1 Pages 47-69
Published: February 20, 1994
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSIn this paper, we propose to use noble gas abundance patterns and isotopic ratios to distinguish between mantle and crustal origin of different types of geological samples. The Kuroko deposits were selected as our first application. The mantle, the crust, and the atmosphere have different noble gas abundance patterns and isotopic ratios. The relative abundances of He and Ne are high in the mantle. The heavy noble gases-Ar, Kr and Xe-are enriched in seawater and seawater-related products. The 3He/4He and 129Xe/130Xe isotopic ratios are usually higher for the mantle than for the atmosphere and the crust. These properties may be used to distinguish the source of geological samples. In this work, the abundances of Ne, Ar and Xe and the isotopic ratios of Ar and Xe were determined for 18 Kuroko ore samples. The concentrations of Ne, Ar, and Xe in the Kuroko ores are like those of magmatic rocks. The abundance pattern of noble gases in the Kuroko ores parallels that of mantle-derived samples. Distribution coefficients of noble gases were calculated from two submarine diabase samples that equilibrated with seawater. Assuming these solid-liquid distribution coefficients can be applied to Kuroko and other magmatic rocks, we calculated the noble gas concentrations of their hypothetical source fluids. The results were used to compute the relative contributions of magmatic source fluid and seawater to the Kuroko ore-forming fluid. Based on Xe data, the relative contributions of magmatic source and seawater to the Kuroko ore fluid are calculated to be 75% and 25%, respectively.View full abstractDownload PDF (6276K)
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