GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
42 巻 , 2 号
選択された号の論文の7件中1~7を表示しています
  • XIAOYAN HU, XIANWU BI, RUIZHONG HU, LINBO SHANG, WENLING FAN
    2008 年 42 巻 2 号 p. 141-150
    発行日: 2008/04/20
    公開日: 2010/11/03
    ジャーナル フリー
    The distribution of tin between different granitic silicate melts and coexisting aqueous fluids have been determined at 850°C, 100 MPa and fO2 near NNO. Tin distribution coefficients DSnaq.fl./melt are constrained by the composition of melt. When the starting fluid is 0.1 M HCl, DSnaq.fl./melt decreases rapidly from 0.130 ± 0.090∼0.137 ± 0.016 to 4.22 (±0.47) × 10-3 with the Na2O + K2O mole content and ASI of melt varying from 6.55 to 9.39% and 1.37 to 0.66, respectively, and tin concentrations in aqueous fluids and DSnaq.fl./melt decrease from 9.26 ± 0.56 to 0.220 ± 0.013 μg/g and 3.70 (±0.42) × 10-2 to 1.29 (±0.15) × 10-3, respectively with Na/K mole ratio increasing from 0.43 to 1.57 and nearly constant ASI from 1.04 to 1.10. A series of experiments that use the same K-rich peraluminous haplogranitic melt as starting solid whereas investigate the effects of chlorine and fluorine, the presence of chlorine in aqueous fluids increases DSnaq.fl./melt because of tin complexing, the presence of fluorine in the starting fluid does not significantly influence on DSnaq.fl./melt. For the chlorine experiments, DSnaq.fl./melt shows a positive dependence on the concentration of HCl in the starting fluid with log DSnaq.fl./melt = 2.0247 × log[HCl] + 0.6717 ([HCl] unit is M), and SnCl2 is the dominant tin-bearing complex in aqueous fluid. The results of this experiment showed that the peralkalinity of granitic melt and F-bearing in granite can lead to the enrichment of tin in melt phase, and, therefore, they probably serve as a tin ore reservoir or an important transport medium for tin ore formation, whereas K-rich peraluminous granitic melt and high HCl concentrations in the aqueous fluid phase are favorable for tin partitioning in aqueous fluid.
  • KAZUKI OKANO, KEN SAWADA
    2008 年 42 巻 2 号 p. 151-162
    発行日: 2008/04/20
    公開日: 2010/11/03
    ジャーナル フリー
    Biomarker analyses of aliphatic and aromatic hydrocarbons were conducted on the upper and lower parts of individual mudstones in a turbiditic sequence of the Miocene Kawabata Formation, Yubari, central Hokkaido, Japan. The relative abundances of terrigenous biomarkers such as long-chain n-alkanes, C29 steranes and oleanenes as well as biomarkers produced in coastal areas such as dinosteranes tend to be higher in the lower parts of mudstones than those of the upper ones in the turbiditic sequence. Also, pristane/phytane ratios, which are proxies for depositional environment, significantly vary between the upper and lower parts of mudstones in the turbiditic sequence. These results suggest that these variations reflect the types and phases of transport and redeposition by turbidity systems rather than postdepositional diagenesis. Such heterogeneous distributions in most of biomarker compositions within the mudstone layers may lead to a severe bias for reconstructing paleoenvironment and paleoecology. Nevertheless, the higher plant parameters (HPPs) such as the retene/cadalene ratios are consistently homogenous within the mudstones. Moreover, paleovegetation reconstructed from HPPs are concordant with a previous paleobotanical study. Thus, it seems that these biomarker records in the turbidite sediments are reliable and strongly applicable for reconstructing terrestrial paleovegetation.
  • ZHENGQUAN LU, NABIL SULTAN
    2008 年 42 巻 2 号 p. 163-175
    発行日: 2008/04/20
    公開日: 2010/11/03
    ジャーナル フリー
    A series of empirical expressions for predicting gas hydrate stability, its volume fraction out of pore space and gas hydrate mass-density were established in different systems in consideration of gas composition (CH4, C2H6, H2S) and salinity (NaCl, seawater), and pore size at temperature between 273.15 and 300 K, based on our gas hydrate thermodynamic model (Sultan et al., 2004b, c). Six of the developed expressions for predicting gas hydrate stability were validated against the available published experimental data and they were also compared with other models. At temperature 273.15 to 290.15 K, the ARDPs (Average Relative Deviation of Pressures between the prediction and the experimental data) have shown that these empirical expressions are in agreement with the experimental data as well as other models, indicating their reliability of predicting gas hydrate stability for these systems. At higher temperatures, the empirical predictions for gas hydrate stability do not well reproduce the experimental data, because they are based on van der Waals model. The empirical expressions for predicting gas hydrate stability in the systems of CH4 + H2S + H2O, CH4 + seawater + poresize, CH4 + H2S + NaCl and CH4 + CO2 + NaCl, and for evaluating gas hydrate fraction and its density need further validation due to lack of available published experimental data. However, the empirical expressions for gas hydrate fraction and its density show that the effects of pore size and salinity are negligible; gas hydrate fraction will increase if methane concentration continuously increases relatively in excess of methane solubility and decreases with pressure within gas hydrate stability zone, which is well consistent with data of natural gas hydrates in Cascadia; gas hydrate density tends to increase with ethane percentage and decrease with pressure.
  • EMILIO PASCUAL, TEODOSIO DONAIRE, CHRISTIAN PIN
    2008 年 42 巻 2 号 p. 177-198
    発行日: 2008/04/20
    公開日: 2010/11/03
    ジャーナル フリー
    To evaluate the origin and significance of microgranular enclaves hosted by granites, we present new data on two granitoid series belonging to the Los Pedroches Batholith (LPB), SW Iberian Massif, Spain. The two series in the LPB show a distinct contrast in terms of field, petrographic, mineralogical and geochemical data. This contrast also extends to the enclaves, differing in abundance and other features in each of the series considered. Isotopic measurements, however, including 87Sr/86Sr, εNd and δ18O data, show no significant, inter- or intra-series contrast throughout the LPB. These data lend additional support to an origin of all the granitoid rocks in the LPB from a single, isotopically homogeneous, lower crustal source. We also suggest that differences between microgranular enclaves in the two LPB granitoid series cannot be related to a different degree of participation of mafic rocks in the genesis of the respective groups: in both cases, microgranular enclaves are better interpreted as autoliths.
  • AKIO MAKISHIMA, EIZO NAKAMURA
    2008 年 42 巻 2 号 p. 199-206
    発行日: 2008/04/20
    公開日: 2010/11/03
    ジャーナル フリー
    A new preconcentration technique of Zr, Nb, Mo, Hf, Ta and W has been invented employing coprecipiation with Ti compounds. Silicate samples were digested by HF with addition of Ti. Subsequent drying with HClO4 resulting in complete elimination of fluorine produces Ti compounds (oxide/hydroxides). The sample was then dissolved with dilute nitric acid and centrifuged, and the residual Ti compounds were collected. The Ti compounds forming from 2 mg of Ti without matrix elements concentrate 84-98% of Zr, Nb, Mo, Hf, Ta and W. In 20 mg basaltic and 50 mg peridotitic matrices, the addition of 1 mg of Ti was appropriate and gave yields of 46-69 and 54-79%, respectively, for Zr, Nb, Mo, Hf, Ta and W. Exploiting this preconcentration, sequential separation protocols of Hf, Pb, Sr, Lu, Nd and Sm for isotope analysis are developed with total blanks of 16, 11, 60, 2.4, 3 and 0.4 pg, respectively. The method is suitable for Lu-Hf system studies with capability of simultaneous separation of Pb, Sr, Nd and Sm from the same sample digest as well as isotopic anomaly studies of Zr, Mo and W. As application examples, accurate Lu-Hf data and Pb isotope ratios were obtained for basalt (JB-3) and peridotite (JP-1) by MC-ICP-MS.
  • MI JUNG LEE, JONG IK LEE, WON HIE CHOE, CHUNG-HWA PARK
    2008 年 42 巻 2 号 p. 207-219
    発行日: 2008/04/20
    公開日: 2010/11/03
    ジャーナル フリー
    We present Sr-Nd-Pb isotope data from the Paleocene-Eocene volcanic rocks in King George Island, South Shetland Islands, West Antarctica. The initial isotopic ratios of the analyzed samples display limited variations: 143Nd/144Nd, 0.512790 to 0.512905 (εNd, +4.2 to +6.5); 87Sr/86Sr, 0.703342 to 0.703877 (εSr, -15.6 to -8.0); 206Pb/204Pb, 18.48 to 18.64; 207Pb/204Pb, 15.50 to 15.64; 208Pb/204Pb, 37.99 to 38.41. We interpret these data in combination with previously published trace and isotope data for Meso-Cenozoic volcanic rocks in the South Shetland Islands to gain a better understanding of the geochemical evolution of the mantle source region. The studied rocks are from four volcanic islands and range in age from 143 to 44 Ma. They have high abundances of large ion lithophile elements and light rare earth elements relative to high field strength elements, consistent with products of subduction related magmatism. The systematic inter-island variations are recognized from a comprehensive examination of the trace elements and isotopic compositions. The degree of enrichment of Sr-Nd-Pb isotopic compositions decreases towards younger samples, while the ratios of fluid-mobile elements/HFSE (Sr/Yb, Pb/Yb and U/Yb) gradually increase. The previous studies on these volcanic rocks concluded that the compositional variations of the South Shetland Islands volcanic suites were mainly controlled by two component mixing between altered MORB and Pacific sediments. However, we here propose that the compositional trends observed in the volcanic rocks of the South Shetland Islands can be created from the addition of a relatively constant subduction component to temporally varying heterogeneous mantle sources. The higher radiogenic Pb and Sr isotopes and lower 143Nd/144Nd ratios of the older volcanic rocks from Greenwich and Livingston islands compared to younger rocks can be explained by the significant influence of enriched previously metasomatized mantle material rather than fluids or sediment melts from the subducting slab. In contrast, the geochemical nature of the youngest King George Island volcanic rocks suggests a relatively large contribution of a slab-derived fluid component to the magma generation, but a minor role of the enriched component.
Note
  • JIN-LIANG FENG, LI-PING ZHU, JIAN-TING JU, LI-PING ZHOU, XIAO-LIN ZHEN ...
    2008 年 42 巻 2 号 p. 221-236
    発行日: 2008/04/20
    公開日: 2010/11/03
    ジャーナル フリー
    A heavy dust fell in Beijing on April 16-17, 2006. The dust storm formed in middle and western Inner Mongolia, China, under a strong Mongolian Cyclone. During the dust fall, the near-surface wind speed was insignificant in Beijing. The minimal wind speed at ground level indicates that the dust must have been transported by upper northwestern winds, and the local dust of Beijing contributed little to dust fall. The lack of a contribution from local dust differed from previous dust fall events in Beijing. Therefore, this dust fall provides good information on the dust source. Dust samples colleted during this event and Pleistocene loess samples from the Beijing area were analyzed for magnetic susceptibility, bulk particle and quartz grain size distributions, bulk particle and quartz micro-textures, mineralogy, carbonate content, major element concentrations, trace element and rare earth element (REE) concentrations, and the oxygen isotope composition of quartz. The results indicate the following. (1) The dust of the April 2006 storm derives mainly from surface sediments in middle and western Inner Mongolia, with some minor contributions from anthropogenic emissions from coal combustion and mining. (2) The characteristics of the dust fall in China appear to vary with time and location, which has significance for paleoclimate reconstructions. (3) Many characteristics differ between the dust from 2006 event and Pleistocene loess in Beijing, and implying that the two have different sources. (4) The loess deposits found in Beijing and on the Loess Plateau also appear to differ in provenance.
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