Thirty tektites from East Asia (including Wenchang and Penglei of Hainan Island, Maoming of Guandong, China; Khon-Kaen of Thailand; Bao Loc of Vietnam; Rizal of Luzon, Philippines) have been analyzed for major and trace element contents and Rb-Sr isotopic compositions. All the samples studied are splash form tektites. The trace element ratios Ba/Rb (avg. 3.74), Th/Sm (avg. 2.31), Sm/Sc (avg. 0.43), Th/Sc (avg. 0.99) and the rare earth elements (REE) contents of tektites studied are similar to the average upper continental crust. The chemical data of tektites in this study indicate that they were derived from similar target rocks which may be related to post-Archean upper crustal materials. The tektites from East Asia have high positive ε^Sr(O) values-ranging from 164.2 to 198.6, indicating that they were not dominantly derived from recent young sediments, such as soil or loess. The Ar-Ar ages (736.8 ± 55.5∼814.6 ± 24.4 ka) of tektites of the present study are consistent with the age of other Australasian tektites, which indicates that all Australasian tektites were derived from a single impact event. Previous studies (Koeberl, 1992; Blum et al., 1992; Schnetzler, 1992) and the present chemical data suggest that these tektites are the result of melting at a single site, which is most probably located in the southern part of the Thailand-Laos border. Mixing calculations based on the model suggested by Ho and Chen (1996) for various amounts and combinations of target rocks indicate that the best fit for East Asia tektites is a mixture of 61% greywacke, 32% sandstone and 7% shale.

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Partitioning experiments of rare earth elements (REEs) between calcite and aqueous (CaCl₂ + NaCl) solution at 25°C and 1 atm have been made in order to elucidate the incorporation process of seawater REE into marine limestones. Calcite-supersaturated solution doped with REE was constantly pumped into a reactor, in which calcite seeds and the solution were mixed and CO₂ + N₂ gas was bubbled to allow calcite overgrowths. Absolute values of REE partition coefficients, K_d(REE) = (X_REE/X_Ca)_calcite/([REE]_total/[Ca])_solution, could not be determined because of very small calcite overgrowths and difficulty in evaluating X_Ca. The relative values of K_d(REE) like K_d(REE)/K_d(Gd), however, were determined successfully. K_d(REE) given by [REE]_total depends on REE(III)-carbonate complexation in solution, and does not correspond to a reaction incorporating a specific dissolved REE species into calcite. Hence, here we used K_d(REE)_ω = (X_REE/X_Ca)_calcite/([REECO₃⁺]/[Ca])_solution, which is given by K_d(REE) and REE(III)-carbonate complexation constants. K_d(REE)_ω relates directly to ΔG_r. for the reaction incorporating REECO₃⁺_(aq) into calcite. The series variation of experimental logK_d(REE)_ω shows a convex tetrad effect, suggesting larger Racah parameters of REECO₃⁺_(aq) relative to REE(III) in calcite. The variation also shows a kink at around Pm, Sm and Eu, possibly reflecting a coordination change of REE(III) in calcite across the series. Yttrium is definitely enriched in solution relative to heavy REEs. Using the relative values of experimental logK_d(REE)_ω and REE analyses of upper Paleozoic Japanese Ishimaki and Tahara limestones, REE abundance patterns for seawater coexistent with the marine limestones have been calculated provided that pH, ΣCO₂ and salinity are the same in the ancient and present times. The calculated patterns are quite similar to those for relatively deep waters at around 400 to 1000 m in the modern Pacific. Ishimaki and Tahara limestones are of the seamount-type. Hence, the calculated seawater REE patterns with large negative Ce anomalies suggest that the incorporation of seawater REE into the limestones occurred in moderately deep water, probably because of subsidence of volcanic seamounts that were capped by Ishimaki and Tahara limestones.

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The general chemical characteristics of Japanese groundwaters at depths greater than 200 meters have been classified using geostatistical and geochemical modeling techniques applied to a dataset of more than 200 chemical analyses of groundwater samples from throughout the country. The objective of the evaluations is to identify representative, generic groundwater types that can be used to assess the long-term safety of a geologic repository for the permanent disposal of high-level radioactive wastes (HLW). Five such generic groundwater categories are defined based on observed trends in the concentrations of reactive solutes with increasing concentrations of the mobile tracer Cl^-; FRHP (fresh-reducing-high pH), FRLP (fresh-reducing-low pH), SRHP (saline-reducing-high pH), SRLP (saline-reducing-low pH) and MRNP (mixing-reducing-neutral pH). Multivariate geostatistical methods and geochemical models of evolutionary processes controlling groundwater chemistry indicate, however, that only the FRHP and SRHP groundwaters are both representative of deep groundwater systems in Japan and relevant to subsurface conditions that could exist in a HLW repository. These groundwater types were therefore selected for detailed evaluation in the recent H12 safety assessment of the Japanese disposal concept for HLW.

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This study reports new geochemical and radiogenic isotope data for Pliocene to Holocene (<2.8 Ma) alkaline (trachybasalt, basaltic trachyandesite, and trachyandesite) as well as subalkaline (basalt to dacite) volcanic rocks from the Michoacán-Guanajuato volcanic field (MGVF), located in the west-central part of the Mexican Volcanic Belt (MVB). There is no clear correlation of most geochemical parameters with differentiation indicators such as SiO₂. The rare-earth elements show light-REE enrichment, flat heavy-REE pattern, and absence of Eu anomaly. Depletion of Nb as compared to large ion lithophile elements such as Ba is observed for most rocks, probably suggesting involvement of subducted Cocos or Rivera plate. However, other HFSE such as Zr and Ti and key trace elements such as B and Be, and isotopic data do not support this conclusion. In most binary plots, the MGVF data lie at mantle compositions toward the lower end of subduction-input parameters, as is the case of magmas from well-known rifts; this contrasts with the data for subduction-related Central American Volcanic Arc (CAVA) rocks that clearly show high values of subduction input. The average isotopic ratios of the MGVF rocks show the following ranges: ⁸⁷Sr/⁸⁶Sr 0.70320-0.70439, ¹⁴³Nd/¹⁴⁴Nd 0.51273-0.51298, ²⁰⁶Pb/²⁰⁴Pb 18.62-18.88, ²⁰⁷Pb/²⁰⁴Pb 15.57-15.62, and ²⁰⁸Pb/²⁰⁴Pb 38.32-38.66. There are apparently no significant differences between the isotopic ratios for alkaline and subalkaline rocks, although the Sr and Pb isotopic ratios for alkaline rocks are somewhat higher and Nd isotopic ratios lower than those for subalkaline rocks. The available geochemical and isotopic evidence does not support the origin and evolution of the MGVF magmas by a simple model such as simple fractional crystallization (FC), nor by direct (slab melting) or indirect (fluid transport to the mantle) participation of the subducted Cocos plate. Instead, it appears that the MGVF basic magmas were generated in a heterogeneously veined-mantle source enriched in LILE, HFSE, and REE, but the intermediate and acid magmas could also contain a crustal component.

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The Maoniuping REE deposit is the second largest light rare earth elements deposit (1.45 million tons of REE₂O₃) in China, located in the Panxi rift, Sichuan Province. It is a vein-type deposit hosted within, and genetically related to the Himalayan alkalic carbonatite-syenite complex. The initial ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios from the Maoniuping carbonatites are similar to syenites, which, however, show more radiogenic ²⁰⁷Pb/²⁰⁴Pb ratios. This could not only be attributed to contamination by crustal materials. The Pb-Pb isotope plots from carbonatites and syenites define a linear array between EM1 and EM2. It suggests their sources were located in a heterogeneous lithospheric mantle and produced by the mixture of EM1 with EM2. The initial ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios from fluorites, galenas, pyrites and feldspar are similar to carbonatites and syenites, and different from granites. Their ²⁰⁷Pb/²⁰⁴Pb ratios also plot to between syenites and carbonatites. This suggests the REE ore-forming fluids were derived from carbonatite and syenite magmas. The Pb isotopic results are consistent with a model for REE deposition involving mixing of the F-rich, syenite-derived fluid with Ca-, CO₂-bearing fluid evolved from carbonatite magma. The early fluorites have higher ²⁰⁷Pb/²⁰⁴Pb ratio than the later ones, which shows that the REE ore-forming fluids were not contaminated by country rocks fluids.

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Oxygen and carbon isotopic ratios (δ¹⁸O and δ¹³C) were analyzed for cellulose extracted from tree rings of 5 oak trees (Quercus crispula) and 4 fir trees (Abies sachalinensis) standing in a 1 ha plot of a sub-boreal conifer-hardwood mixed forest, northern Japan. The δ¹⁸O variations were well correlated between individual trees of Q. crispula (canopy trees) and A. sachalinensis (recently grown-up sub-canopy trees), although A. sachalinensis had about 1 ‰ higher δ¹⁸O values than Q. crispula on average and there was an apparent one-year phase lag between δ¹⁸O variations of the two species. The similar inter-annual variation in δ¹⁸O among different individuals and species suggests a common environmental control. Contrary to δ¹⁸O, the inter-annual variations in δ¹³C did not possess any common trends among individual trees for either Q. crispula or A. sachalinesis, suggesting that the ecological effects, such as spatial heterogeneities in δ¹³C and/or concentration of CO₂ in canopy air and/or competition for light with neighboring trees, regulate the δ¹³C of photosynthetic products in each tree. Seasonal variations of the δ¹⁸O and δ¹³C within annual tree rings of Q. crispula showed random and cyclic characteristics, respectively. The difference between the annual patterns of δ¹⁸O and δ¹³C supports the idea that δ¹⁸O is controlled by some environmental factors, which change from year to year, but δ¹³C is primarily governed by physiological conditions of the tree itself, which repeat regularly in every growing season. The historical variation in δ¹⁸O of tree-ring cellulose in Q. crispula has negative correlations with those in both of winter and summer precipitation amounts, whereas it does not show any relationship with temperature, probably due to multiple source areas of water vapor for the precipitation at the studied area. Because the δ¹⁸O of precipitation in northern Japan is positively correlated with air temperature, the correlation between δ¹⁸O and winter precipitation suggests that, in a year of heavy snowfall, the soil in this forest retains larger amount of lower δ¹⁸O water derived from snowmelt, which is taken by roots of Q. crispula in summer. On the other hand, the negative correlation with summer precipitation cannot be elucidated by the δ¹⁸O of rainfall, but must be explained by a higher relative humidity in the growing season in a year of larger summer rainfall. Our results confirm the potential of δ¹⁸O of tree-ring cellulose to reconstruct past climate in a forest with a heavy snowfall, and suggest the importance of the hydrological knowledge in an atmosphere-soil-plant system for the utilization of tree-ring δ¹⁸O in paleoenvironmental purposes.

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Molecular and carbon isotopic compositions of atmospheric polycyclic aromatic hydrocarbons (PAHs) were measured in sites at 1 m (S1), 10 m (S2) and approximately 200 m (S3) distant from roads in Tokyo, Japan. Total suspended particles (TSP) concentrations at S1 was approximately three times higher than S2 and S3, while the concentration of atmospheric PAHs was almost the same (76-166 μg g^-1-TSP) at S1, S2 and S3. Compound-specific δ¹³C of atmospheric PAHs ranged from -23.3 to -24.5‰ at S1, from -24.1 to -25.6‰ at S2, and from -25.2 to -27.0‰ at S3. The concentration of some PAHs and the weighted averages of δ¹³C of some selected PAHs differed significantly among the three sites. The PAH concentration ratios indicating automotive contribution were S1 > S2 > S3, while the ratios indicating non-vehicle contribution were S3 > S2 > S1. These differences in molecular and isotopic signatures among the three sites are not caused by photolysis, instead they are possibly due to differences in the sources of PAHs. A quantitative approach to identify compound-specific sources is to use the concentration and δ¹³C of individual PAHs at each site. The estimated average δ¹³C values of individual PAHs derived from automobiles, which was calculated using a mass balance model, ranged from -19.5 to -23.6‰. Taking into account the results of this study and those of previous studies, -26 to -28‰ was adopted as the δ¹³C value of PAHs derived from non-vehicle sources. We estimated that the automotive contribution to the concentration of individual PAHs ranged from 33 to 88% at S1, from 11 to 74% at S2, and from 0 to 52% at S3. We conclude that compound-specific δ¹³C measurement is a powerful and useful tool to identify such compound-specific sources of atmospheric PAHs.

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