[en] The thermodynamic distribution coefficient of cadmium between calcite and solution has been determined from the measurement of the apparent distribution coefficient in the calcium bicarbonate solutions containing cadmium ions and bipyridine as a complexing agent with the cadmium ions. The distribution of cadmium ions for aragonite in the solution containing magnesium ions (Mg²⁺:1.2 g/l) has also been examined. The value of the thermodynamic distribution coefficient of cadmium between calcite and solution was estimated to be about 20. When the amount of cadmium coprecipitated with aragonite was expressed in terms of distribution coefficient, the value for aragonite is about 1.5. The coefficient of cadmium was not able to be obtained from the apparent distribution coefficient observed in the calcium bicarbonate solution containing bipyridine and cadmium ions, even with aid of the exact stability constants of the complexes between cadmium ions and bipyridine. It was revealed that the thermodynamic distribution coefficient for cadmium was not constant, although constant values were obtained for magnesium, copper, zinc, manganese, strontium, barium and other divalent ions. (Kobatake, H.)

[en] We conducted a sequential chemical extraction experiment for radiocesium ("1"3"4Cs + "1"3"7Cs) using 21 surface sediment samples and two sets of size-fractionated surface sediment samples collected offshore Fukushima. Our results support earlier reports in this area that organic substances in marine sediments have an apparently higher preference for radiocesium than mineral substances. Observations suggest that mineral and organic substances in the marine sediments offshore Fukushima have the same order of preference for radiocesium, primarily because of the existence of ionic competitors in seawater. The apparent preference of radiocesium for organic material is greater because of the partial coverage of sediment mineral surfaces by organic substances. By using these relationships, we created a 2-D map of radiocesium concentration in sediment organic fraction in offshore-Fukushima region. Combining our results with existing monitoring data of marine benthos in offshore-Fukushima sediments, we estimated a transfer coefficient of radiocesium from sediment organic materials to benthic polychaetes as less than 0.03-0.008. (author)

[en] The Zhantang andesites, which erupted in the Late Cretaceous Huichang Basin of SE China interior, were associated the the Late Mesozoic lithospheric extension and basaltic underplating. They are high-Na(6.59-8.46 wt% Na₂O), high-Al trondhjemitic rocks with high Sr and Ba, low Y and HREE, and high Sr/Y and La/Yb ratios, similar to modern adakites. However, they are much higher in Na₂O but lower in CaO than adakites. Their εNd(T) values of -2.3 to -3.8 and initial ⁸⁷Sr/⁸⁶Sr ratios of 0.707 to 0.708 are also significantly different from those of adakites with MORB-like isotopic compositions. These chemical and isotopic features, along with the tectonic setting, suggest that they were not produced by partial melting of subducting slab. The Zhantang adakite-like magmas may be derived from underplated basaltic lower crust, but require a compositionally peculiar basaltic protolith to account for their extremely high-Na and low-Ca feature. They are compositionally comparable to the experimentally produced partial melts of alkali-rich basalt. We therefore interpret them as the products of melting of an alkali-rich basaltic rock. (author)

[en] We report here the first synchrotron radiation (SR)-based X-ray absorption fine structure (XAFS) spectra for Os at L_III-edge in geo- and cosmo-chemical materials. Samples were Negrillos meteorite, a II-A type iron meteorite, and a Pt ore specimen, aggregates of coarse grained Pt-Fe alloys, from the Choco district, Columbia. X-ray absorption near-edge structure (XANES) spectra of Os are presented for Negrillos, which has an Os abundance of 65 ppm, as well as for the platinum-group mineral (PGM). The XANES spectra showed that Os in the iron meteorite and the PGM chiefly exist as a metallic species. The average interatomic distance of Os in the Pt ore from the Choco district are calculated from the EXAFS spectra. The results suggest that the neighboring atoms of Os are not Pt. Instead, they are most likely Os and Ir. This is consistent with the common occurrence of fine lamellae of Os and iridosmine as exsolution products of Pt-Fe alloys. Furthermore, this confirms the limited solubility of Os in Pt-Fe alloys. EXAFS could thus be useful for identifying the host phases of Os in natural samples. This study has verified that the chemical state of Os in natural samples can be determined using XAFS. It is expected that further application of the XAFS technique to Os speciation in natural samples will help to elucidate Re/Os fractionation processes in the Re-Os isotopic system. (author)

[en] Petrographic, petrochemical and Sr-Nd isotopic data are presented for granitoids and microdioritic enclaves from two Cretaceous stocks (Togouchi granodiorite and Tateiwayama granite porphyry) from the Togouchi-Yoshiwa district, northwest Hiroshima prefecture, SW Japan. The data are used to examine the genetic relationships between the microdioritic enclaves and their granitoid hosts. The granodiorite, granite porphyry and the microdioritic enclaves are all calc-alkaline in nature, and belong to the I-type ilmenite series. The Togouchi graniodiorite has a Rb-Sr whole rock isochron age of 85.6±4.7 Ma with an initial Sr isotope ratio (SrI) of 0.70634±0.00012 (2σ). The Tateiwayama granite porphyry has a slightly younger Rb-Sr whole isochron age (77.4±3.1 Ma) but similar SrI of 0.70653±0.00015, suggesting that both stocks may have been derived from the same source. Despite diverse whole rock chemistry, the microdioritic enclaves in the respective intrusives have quite similar initial Sr and Nd isotope ratios, suggesting that they formed by fractional crystallization of a single magma, and also that the source of the enclaves in both intrusives had similar geochemical characteristics. In both stocks, however, the enclaves have distinctly lower initial Sr isotope ratios than their respective host rocks, indicating that they were derived from a different source than their hosts. In view of the geochemical and Sr-Nd isotope data, we infer that the enclave magmas were derived from a similar LILE- and LREE-enriched source to that of the Cretaceous basalts and gabbroic-dioritic rocks that are sporadically distributed in SW Japan. Such mafic to intermediate magmas were probably derived from the upper mantle, and transferred both heat and material to the lower crust, thus producing granitic magmas by partial melting. Successive mafic magmas or their differentiates could then have been injected into the granitic magma chamber, trapped and quenched, resulting in the formation of microdioritic enclaves in both granitic stocks. (author)

[en] ⁸⁷Sr/⁸⁶Sr ratios of acid-washed residues of the loess and paleosols since 40 ka B.P. from the Huanxian profile of the Loess Plateau, China, were determined. The investigation shows that ⁸⁷Sr/⁸⁶Sr ratios of the residues from the loess levels are generally lower than those from the paleosol levels. It is though that the paleosol contain a higher proportion of the fine grain size parts (<2 um) than the loess. A correlation occurs among the variations in ⁸⁷Sr/⁸⁶Sr ratios. Zr/Rb ratios and mean grain size and, collectively they, imply that the East Asian winter monsoon was weak about from 40 ka B.P. to 30 ka, but it became stronger from about 30 ka B.P. to 10 ka B.P. Heinrich events of the North Atlantic region and Greenland correspond well to low ⁸⁷Sr/⁸⁶Sr ratios of residues of the Huanxian profile, which demonstrates that Heinrich events also influenced the east Asian region, including the Loess Plateau of China, and ⁸⁷Sr/⁸⁶Sr ratios of residues of the Loess Plateau can record information on high-frequency oscillations of the east Asian winter monsoon strength. (author)

[en] The cosmogenic xenon isotope patterns were calculated independently for each temperature fraction from Patwar and also for the Estherville mesosiderite data of KAISER and RAJAN. A distinct correlation with temperature was observed which is comparable to other results on achondrites and lunar materials. These spallation product compositional variations appear to depend on target and energy variations. Cosmogenic yields of ¹²⁹Xe are also distinctly correlated, suggesting an insignificant contribution of radiogenic ¹²⁹Xe, i.e., from extinct ¹²⁹I decay. The ¹²⁹Xe/¹²⁶Xe spallation ratio varied from 0.7 in the high temperature fractions from Estherville to about 1.8 in the low temperature fractions from Patwar. (author)

[en] The isotopic compositions of Ca, Ba and Nd in the Allende inclusion EK 1-4-1 resemble those of the terrestrial Ca, Ba and Nd exposed to neutron flux. The values of thermal neutron-capture cross-section were used previously to calculate the variations of the isotopic ratios. Much improved agreement between the calculated and observed isotopic ratios can be obtained if the 15 keV cross-section values for the neutron-capture processes are used. The results from the calculations of the isotopic anomalies observed for Ca, Xe, Ba and Nd are described. The isotopic anomalies of Ca, Ba, Nd and Xe observed in meteorites are explained as those due to the alteration of the isotopic ratios by the combined effect of mass fractionation, neutron-capture and cosmic-ray irradiation processes, which took place prior to and during the period of formation of the solar system. The neutron-capture process appears to have occurred at a temperature higher than that on the earth surface. (J.P.N.)

[en] The proper computation of the correlation coefficients is discussed for some of the possible diagrams used for U, Th-Pb geochronology and some of the common methods of measuring the isotopic composition of lead. It is then demonstrated that by the simple modification of the method of presenting the data, the correlation coefficient for Pb-Pb dating can be reduced either identically or effectively to zero, so that the simpler, zero correlation, two-error line fitting algorithm can be used. Formulae are derived for the correlation of errors in the most used lead-lead and uranium-lead diagrams. It is emphasized that with the usual measurement schemes, error correlation is high in the conventional diagrams. An inverse lead-lead diagram is described, in which, by the proper choice of the measurement scheme, there is no correlation between errors. This advantage is gained whilst maintaining the use of a measurement scheme which optimises the precision of lead isotope measurements. (J.P.N.)

[en] Semiquantitative eigenvector analysis demonstrates that the differentiation of individual lanthanoids occurs in sedimentary environment. By means of eigenvector diagrams, the degree of lanthanoid fractionation can be expressed semi-quantitatively. Recent papers lend support to the idea that under given circumstances, the elements of lanthanoid group (La - Yb) can be differentiated by geological processes. In the present study, eigenvector analysis was used for the investigation of the behaviour of lanthanoid elements in clays and bauxites. The material for the present study was three series of samples. Two of them were clays derived from the same geological source area, and they were different mainly by the natural conditions under which they had been deposited. The third sample set was bauxite, so rich in hematite that it is nearly iron ore with economic value. (J.P.N.)