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We have measured the Ca and REE compositions of seven kimuraite samples, which are subsamples taken from a spherulitic aggregate kimuraite sample filling a void in the alkali olivine basalt. In the chondrite-normalized REE patterns, all samples yielded parallel concave tetrad patterns, and the mole ratios of Σ(REE+ Y) to Ca were calculated to be 2.5 to 3.4, all of which were obviously larger than the ideal value 2.0 of kimuraite. In addition, electron-probe microanalyzer (EPMA) was also applied to determine the compositions of our samples. Though only four rare earth elements (Y, La, Pr and Nd) were able to be measured, the mole ratios of Σ(REE+ Y) to Ca of thirty-two point analyses determined with EPMA were 2.1 to 3.3. Both analytical results demonstrated that our kimuraite samples might have excessive amount of REE. In the backscattered electron (BSE) images, besides dark kimuraite grains, the presence of another mineral with brighter BSE intensity along the cleavages of kimuraite grains was confirmed, and almost all analysis spots of EPMA failed to escape from the contamination of this mineral. The most possible candidate for this mineral is lanthanite, both for its close association with kimuraite and for its characteristic chemical composition. The compositions of our kimuraite samples, especially LREE, have been modified due to the presence of a small portion of lanthanite, but the concave tetrad pattern remains, as lanthanite seems to have a similar concave tetrad pattern like kimuraite.

The REE abundance patterns for lanthanite-(Nd) [(La, Nd)z(CO3)3·8H2O] and kimuraite-(Y)[CaY2(CO3)4·6(H2O)], have been examined by Jørgensen-Kawabe equation for the lanthanide tetrad effect. The reported REE data for lanthanite-(Nd) samples from the Whitianga quarry, New Zealand (Graham et at., 2007) and Hizen, Higashi Mastuura, Japan (Akagi et al., 1996), give their chondrite-normalized REE patterns which can be regressed successfully by the theoretical equation, except for their Ce anomalies. When the lanthanite-(Nd) from Whitianga is normalized by the Hizen Ianthanite, their strong trends of light REE enrichment are cancelled mutually, leaving a small convex tetrad effect in the REE pattern. Two kimuraite-(Y) samples coexisting with the Hizen lanthanite-(Nd) show similar W-type tetrad effects (Akagi et al. 1993). One kimuraite-(Y) sample, in fact, exhibits a typical tetrad effect, but the other kimuraite-(Y) shows a less symmetrical one. The REE pattern for the former kimuraite, when normalized by chondrite or by the Hizen lanthanite, is immediately regressed by the theoretical equation, but the REE pattern for the latter kimuraite cannot be fitted to the equation without correcting for light REEs. The excesses of light REEs in the latter kimuraite are evaluated by the regular REE fractionation between kimuraite and lanthanite and the theoretical equation. The REE patterns for lanthanite-(Nd) and kimuraite-(Y) with the tetrad effects are certainly described quantitatively by Jørgensen-Kawabe equation, signifying its importance in considering the REE distributions in the representative rare earth minerals of lanthanite-(Nd) and kimuraite-(Y).

Groundwater gas anomalies were observed at the 1,500 m deep Nagashima spa well near Nagoya for the M=5.7 earthquake (Oct. 31, 2000) in southern Mie Prefecture, Japan. In spite of the very long focal distance of 98 km, H2/Ar, He/Ar, N2/Ar, and CH4/Ar ratios of groundwater gas bubbles significantly changed not only at the time of the shock but also 3 days before it. Water temperature indicated a sharp coseismic increase. The earthquake was a dip-slip reverse event occurred approximately beneath the plate boundary in the eastern part of Kii Peninsula at 44 km depth. The gas anomalies are strikingly different from the previous ones at the same well, which were restricted to those in H2/Ar ratio for nearby events with M=1.6-5.4 within 25 km. The apparently "long-distance" nature of the groundwater gas anomalies may suggest a coherent subsurface deformation over a roughly 100 km x 100 km area. In view of the size and occurrence timing, we speculate that such a subsurface episode may possibly be related to the onset of unsteady crustal displacements of the 2001 Tokai silent earthquake revealed by the nationwide GPS observation system.

Our REE data for a Pacific MORB sample by ICP-AES and recently reported REE data by ICP-MS for MORB from Atlantic, Pacific, and Indian Oceans strongly suggest that MORB show small concave tetrad effects in their chondtite-normalized REE patterns irrespective of normal and enriched types. The Cenozoic alkali olivine basalt sample from western Kyushu, Japan, which is the host basalt of the secondary REE carbonate mineral of kimuraite, also indicates an obvious concave tetrad effect in its chonchite-normalized REE pattern. When the alkali olivine basalt sample is normalized by another alkali olivine basalt sample (JB-1) belonging to the same volcanic suite, there can be seen a concave tetrad effect again, suggesting a tetrad phenomenon involved in the Cenozoic mafic volcanic activity in western Kyushu. The REE patterns for MORB and the alkali olivine basalt normalized by CI chondrite or JB-1 can be fitted to the theoretical equation for tetrad effects (Kawabe, 1992) with or without correcting certain "irregularities" in La and Ce. The chondrite-normalized REE patterns for MORB and the alkali olivine basalt become more concordant with their tetrad effect variations, when the CI chondritic Tb, Ho and Tm abundances by Anders and Grevesse (1989) are corrected to slightly smaller values by -4, -5, and -3%, respectively. This is compatible with the latest REE analyses of meteoritic, lunar, and terrestrial samples by ICP-MS. The theoretical equation can fit the chondrite-normalized REE patterns for MORB and the alkali olivine basalt, although empirical corrections for La and Ce are sometimes necessary. This is implying that the genesis of MORB and that of the western Kyushu alkali basalt accompanies rather simple REE fractionation processes.

The Late Cretaceous (ca. 67 Ma) Naegi granite-pegmatite suite in Nakatsugawa City, Gifu Prefecture, central Japan, has been studied in view of the lanthanide tetrad effect in evolved felsic rocks. The pegmatite occurring sparsely in the granite body as small patches (, 国立情報学研究所で電子化したコンテンツを使用している。

The hydration state of light REE^3+(aq) is changing across the series, and each light REE^3+(aq) is a mixture of two distinguishable species of nonahydrate and octahydrate in equilibrium with respect to the hydration change reaction of light REE^3+(aq). Two sets of thermodynamic data for the hydration change of light REE^3+(aq) at 25℃ and 1 atm have been reported: one is the data set for the reaction [REE(H_2O)_8]^3+(aq)+H_2O(1)=[REE(H_2O)_9]^3+(aq) evaluated by Miyagawa et al. (1988) on the basis of the hydration enthalpies and free energies for the two hydrate series calculated from electrostatic bonding energies and Born’s hydration theory. The other is the data set for the conventional reaction that octahydrate REE^3+(aq)=REE^3+(aq), which was evaluated by Kawabe (1999a) from the thermodynamic data for solution of the fully isomorphous series of REE(ES)_3・9H_2O(ES=C_2H_5SO_4^-) and the partly isomorphous ones of REECl_3・nH_2O (n=7 for La – Pr and n = 6 for Nd – Lu) and their least-squares fittings to the improved RSPET (refined spin-pairing energy theory) equation. Here is shown that the thermodynamic parameters for the two reactions are readily convertible, and that the standard-state ΔG^0_γ values for [REE(H_2O)_8]^3^+(aq)+H_2O(l)=[REE(H_2O)_9]^3+(aq) from Kawave (1999a) are more acceptable than those calculations by Miyakawa et al. (1988) when referred to the X-ray diffraction studies of hydrated REE^3+ in REE(III) chloride solutions. The ΔG^0_γ values at elevated temperatures up to 250℃ have been calculated using the standard-state ΔH^0_γ and ΔS^0_γ for the reaction and the equation by Helgeson (1967 and 1969). The theoretical estimates are compatible with our recent experimental results of REE(III) partition coefficients between Fe(III) oxyhydroxide and aqueous solution in hydrothermal conditions. The series variations of logarithmic equilibrium constants for all the geochemical reactions involving REE^3+(aq) are affected by the hydration change of REE^3+(aq), but the hydration change effect can be separated from the over-all series variations using the thermodynamic parameters calculated in this study., 国立情報学研究所で電子化したコンテンツを使用している。

Light REE^3+(aq) is a mixture of two distinguishable species of nonahydrate and octahydrate in equilibrium with respect the hydration change reaction that [REE(H_2O_8]^3+(aq)+H_2O(I)=[REE(H_2O)_9]^3+(aq), and the apparent hydration number of light REE^3+(aq) is changing across the series. Here is discussed nephelauxetic effects of the two REE^3+(aq) series from ΔH^0_γ data for the hydration change reaction and the tetrad effect variations of their hydration enthalpies (ΔH_hyd.) and REE-OH_2 distances. The ΔH^0_γ data combined with those data for solution of REE(ES)_3・9(H_2O) with ES = C_2H_5SO_4^- reported previously, suggest that Racah (E^1 and E^3) parameters for light REE^3+ like Nd^3+ decrease in the following order:[REE(H_2O)_9]^3+(aq)>REE(ES)_3・9(H_2O)> [REE(H_2O)_8]^3+(aq). The average REE^3+-OH_2 distance also decreases in this order. Hence this is a nephelauxetic series that Racah parameters are reduced with decreasing REE^3+-OH_2 distance. The Racah parameters for [REE(H_2O)_9]^3+(aq) series are fairly large and comparable with those of gaseous free REE^3+. No significant tetrad effect is expected in its series variation of (-ΔH_hyd.). By contrast, [REE(H_2O)8]^3+(aq) series has significantly smaller Racah parameters than gaseous free REE^3+, and a convex tetrad effect is expected in the series variation of (-ΔH_hyd.). Since (-ΔH_hyd.). of [REE(H_2O_8)]^3+(aq) in heavy REE series is fitted to a linear function of the reciprocal of observed REE-OH_2 disrance in REECl_3 solution, this relation has been extended to light REE series, and a similar relation for [REE(H_2O)_9]^3+(aq) in light REE series has also been determined from our thermodynamic mixture model and observed REE-OH_2 distances in REECL_3 (REE=La, Pr and Nd) solutions. The reciprocal of REE-OH_2 distance in [REE(H_2O)_8]^3+(aq), when plotted against the atomic number of REE, indicates a small convex tetrad effect whereas such an effect is absent in [REE(H_2O)_9]^3+(aq) , in accordance with their nephelauxetic effects. Interestingly, (-ΔH_hyd.) of [REE(H_2O)_9]^3+(aq) satisfies a linear function of 1/(REE-OH_2), and at the same time, the series variations of both (-ΔH_hyd.) and 1/(REE-OH_2) exhibit small convex tetrad effects when plotted against the atomic number of REE. This is analogous to the relationship between the lattice enthalpy of REEO_1.5(cubic) and REE-O distance. The property of (-ΔH_hyd.) and the lattice enthalpy of REEO_1.5 can be understood from the viewpoints: i) the existence of REE(III) cluster with the equilibrium configuration having the minimum energy by itself, and ii) the classical limit in quantum-chemical energetics where Planck’s constant (h) equals zero. It is emphatically noted that the observed tetrad effects and RSPET can complement the classical ion model with a tactic by which internal structures of the real REE^3+ ions are legitimately introduced into our thermodynamic discussion., 国立情報学研究所で電子化したコンテンツを使用している。

The Kuzuu limestone-dolostone complex, in central Japan, is a remnant of the Middle Permian carbonate succession formed on a basaltic seamount in an open-sea realm without inputs of terrigenous materials. REE and Sr isotopic data of the carbonate rocks are clues to understanding the diagenetic process of biogenic carbonates to form crystalline carbonate minerals. The 87Sr/86Sr ratios of bulk carbonate samples are 0.7073-0.7076, and their Sr isotopic stratigraphic age (260±5 Ma) coincides with their fusulinid fossil age (263±8 Ma). The carbonate rocks have much higher REE/Ca ratios than modern skeletal biogenic carbonates by factors of 10^2-10^4. Their REE/Ca ratios are about one order of magnitude higher than those of microbialite. The chondritenormalized REE patterns for the Kuzuu samples show large negative Ce anomalies, together with seawater-like tetrad effects and high Y/Ho ratios. The Ce anomalies are comparable to those of present-day ocean waters at depths of 600-800 m, except for the bottom part samples polluted with Fe(III) oxyhydroxide possibly by fluids derived from underlying basaltic volcanics. Their REE patterns normalized by Pacific seawater at a depth of 381 m exhibit smooth light REE enrichment trends similar to the experimental partition coefficients of REE between calcite-overgrowths and seawater solutions. There is no significant difference in REE and Y features between the limestone and dolostone members. The original biogenic carbonates deposited on a basaltic seamount in shallow water environment, but subsequently they were subsisted to the water depths suggested by their Ce anomalies. At the water depth, the biogenic carbonates were re-crystallized to calcite under a condition of sufficient supply of the seawater, and the seawater REE and Y were incorporated into calcite. The 87Sr/86Sr ratios of dolomite, however, are slightly lower than those of coexistent calcite by 0.0002, which is a time interval of about 2 Ma from the seawater 87Sr/86Sr curve for Middle to Late Permian. The dolomitization occurred almost immediately after the re-crystallization on biogenic carbonate to calcite in a moderately deep water, but did not alter the REE and Y features of limestone precursors. This is consistent with the recent diagenetic model for the carbonate sequences of Neogene atolls in the Pacific emphasizing the role of thermal convection of moderately deep water., 国立情報学研究所で電子化したコンテンツを使用している。

Six samples of ferromanganese nodules taken from a knoll and a seamount off Wilkes Land, Antarctica, have been analyzed by ICP-AES and their geochemical characteristics have been compared with those of Pacific nodules. The Antarctic nodules have slightly concentric structures with rough surface texture similar to those of early diagenetic Pacific ferromanganese nodules. However, mineralogy, transition metal contents (Mn, Fe, Ni and Cu) and the rare earth element (REE) patterns, suggest that the Antarctic nodules are more similar to hydrogenous Pacific ferromanganese nodules. The Antarctic nodules have higher values of positive Ce anomalies and Co/(Ni+Cu) ratios, but have lower Mn, P, Ni, Cu and V contents than hydrogenous type Pacific nodules. In addition, the Mn content correlates with the Co content in the Antarctic nodules. These features suggest that the Antarctic nodules contain hardly any diagenetic component. This is possibly related to the fact that all Antarctic samples were collected above the CCD. In the Antarctic Ocean, biogenic productivity is generally high, but most of the organic material is decomposed before it reaches the sediment because of the high oxygen content of the water column in the Antarctic Ocean. The Antarctic samples represent more hydrogenous materials even when compared with the hydrogenous nodules from the Pacific Ocean., 国立情報学研究所で電子化したコンテンツを使用している。

A new station for seismo-geochemical observation has been installed at a 1,500 m bore-hole well of Nagashima spa in a southwestern suburb of Nagoya, central Japan. The well is located in the Yoro-Ise Bay active fault zone. Gas bubbles are separating from groundwater being pumped constantly at the well. In November 1997,we started automated monitoring of H_2,He, Ar, N_2,CH_4 and Rn in the gas bubbles by using a gas chromatograph and an α scintillation Rn monitor. Even in a short monitoring period less than one year, similar preseismic increases in the H_2 concentration have been recorded for nearby microearthquakes (M=1.6,1.9,2.0 and 2.6) and small and moderately large events (M=3.8 and 5.4) within the focal distance of 25 km. All the six events occurred in parallel with the Yoro fault several kilometers apart in the west. In particular, three microearthquakes before the M=5.4 event and the moderately large event itself accompanied conspicuous H_2 anomalies. Preseimic increases in the H_2 concentration up to 100% during a few to several weeks were followed by spike-like increases of H_2 concentration of 10-100% immediately after the respective four shocks. No comparable anomalies were seen in the gas species other than H_2. The preseismic increases in groundwater H_2 are plausibly geochemical diagnostics of the stress corrosion process preceding earthquakes. The preseismic H_2 anomalies for the two events (M=3.8 and 1.9) after the M=5.4 shock were less conspicuous than those for the other four events. The background-level of H_2 concentration also decreased significantly after the M=5.4 event. The subsurface H_2 behavior may have reflected the stress condition in the Yoro fault zone altered by the M=5.4 earthquake., 国立情報学研究所で電子化したコンテンツを使用している。

Our study of geochemical mapping in the area of Toyota and Seto Cities, Aichi Pref., central Japan, has been further extended. This geochemical mapping, started in 1994 for the purpose of environmental assessment of this area, is based on chemical data of stream sediments of drainage systems distributed over the area. Cretaceous granitic basements occur widely in the eastern part, whereas late Cenozoic sedimentary rocks cover the basements in the western part. In 1996,we have extended the mapped area to the northeastern part of Toyota City, and collected new 66 samples. Since 1994,we have sampled stream sediments from 352 different locations in the area of approximately 25 km × 25 km. All the samples have been analyzed for Al, Ti, P, Ni, Co, V, Sr, Cu, Cr, Ce and Zn by ICP-AES and for K, Na, Fe, Ca, Mg and Mn by AAS. In addition, representative samples of three different types of Cretaceous granites and their biotite mineral separates were analyzed. It turned out that chemical compositions of stream sediments in the areas of Creataceous granitic basements are systematically different from those in the areas of sedimentary rocks : (1) The Ca/Ti ratio and Ca, Na and Sr abundances in Cretaceous granitic basements are higher than those in the areas of the sedimentary rocks. (2) Cr, Co, Cu, Ni, V and Zn are depleted in the stream sediments from the granitic basements relative to the sedimentary rock areas. (3) The areal distribution patterns of the Ca/Ti ratio and the elemental abundances coincide with the distribution of the Cretaceous granitic basements. The geochemical results are fairly reasonable, because the sedimentary rocks have experienced much more intensive weathering reactions than the Cretaceous granitic rocks. During weathering of granitic rocks, plagioclase is more readily decomposed than biotite. Hence, as the weathering proceeds, the abundance of biotite relative to plagioclase increases in weathered rocks. As a result, the clastic materials transported into sedimentary basins tend to be depleted in Ca, Sr and Na because these cations are contained mainly in plagioclase. But such clastics become enriched in Ti, Cr, Co, Cu, Ni, V and Zn because biotites still accommodate these cations. This inference is consistent with our analyses of representative samples of granites and their biotite mineral separates. The areal distribution of Ce, however, does not show such a systematic difference between the two geologically different areas. Finer grains of Ce-rich rare phases such as monazite, allanite and/or sphene may be responsible for the areal distribution pattern of Ce abundance in the stream sediments., 国立情報学研究所で電子化したコンテンツを使用している。

The CO_2-bubbling method for extracting gases dissolved in water samples has been reexamined in order to apply it to monitoring of dissolved gases in groundwaters. Dissolved He, Ne, Ar and N_2 in water equilibrated with the atmospheric air in a temperature range of 13-31℃ were extracted by the method, and gas chromatographically determined. The measured values for dissolved atmospheric He, Ne, Ar and N_2 show temperature variations in parallel with the calculated ones from their solubilities, but they are systematically higher than the calculated values by 18% for He, 11% for Ne, 6% for Ar and 8% for N_2. Although the CO_2-bubbling method is effective and convenient for extracting the dissolved gases in the field, appreciable amounts of blanks are associated with it. The blank sources of He, Ne, Ar and N_2 are the dissolved air in HCl and NaOH solutions used in the method and the direct air contamination. The extracted gas by the method contains H_2 and CH_4 from fluid inclusions of the marble dissolved in the extraction process to generate CO_2 for stripping. The blank H_2 and CH_4 depend on the nature of inclusions in the used marble and on the amount of the marble dissolved. We also found that the fine marble grains and particles formed by crushing and grinding retain significant amounts of tribochemically produced H_2. Such fine marble grains and particles should be removed completely from granular marble used in the extraction. When the CO_2-bubbling extraction is applied to routine analyses of dissolved gases in groundwaters, it is important to minimize such blank gases and to make reliable corrections for them., 国立情報学研究所で電子化したコンテンツを使用している。

An ultrasonic nebulizer used in ICP-AES analyses of REE, Y, and Sc improves analytical sensitivities for the elements by one order of magnitude relative to the conventional pneumatic nebulizer. The detection limits (the concentrations corresponding to 3σ-background variations) by ICP-AES with the ultrasonic nebulizer range between 0.05 ppb and 0.5 ppb for Eu, Tm, Yb, Lu, Y, and Sc, and between 0.5 ppb and 5 ppb for La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er. Only for Pr, the detection limit is 10 ppb. The detection limits correspond to about 2% of the chondritic abundances or less, except for Pr and Tb. No significant memory effects have been found in the ultrasonic nebulizer. It takes 50 to 60 sec to clean out a sample solution after its measurements. The clean-out time is only about twice that of the conventional pneumatic nebulizer. Intermittent injections of dilute HF solution (0.5%) are so effective to maintain a quartz transducer clean. This makes its nebulization efficiency approximately constant. The ultrasonic nebulizer can be applied to routine ICP-AES analysis of REE, Y, and Sc in a wide spectrum of geochemical samples in couple with adequate wet chemical techniques for their group separation. Ar gas and sample solutions consumed by the ultrasonic nebulizer in each run are about twice as much as those by the pneumatic one. To save running cost and sample solutions, it is better to use the ultrasonic nebulizer as a complement to the conventional pneumatic one only for a limited number of REE which are relatively insensitive and less abundant like Pr, Tb, Ho, and Tm. Some examples of our application are presented., 国立情報学研究所で電子化したコンテンツを使用している。

Stream sediments in the Sanage-yama area, Aichi Prefecture were examined for the environmental assessment of the area. A total of 128 samples were analyzed for sixteen elements including Al, Ca, Ce, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Sr, Ti and V with ICP atomic emission spectrometry and atomic absorption spectrometry. Areal distributions and cumulative frequency distributions of the elements were discussed in view of sources for the elements. Samples from the area where granitic rocks are exposed are rich in Al, Ca, Na and Sr. On the contrary, Co, Cr, Fe, Ni and V are enriched in samples from the area underlain by Tertiary sediments. The distributions of these nine elements are considered to be closely related to the exposed rocks. Concentrations of Cu, Fe, Mn, Ni, and P are high in samples from some places without any correlation to the geology. Natural backgrounds of the elements seem to be overlaid with the elemental dispersion due to human activities. Drainages from human activities and many china-ware factories in and around Seto City are the main sources for some elements such as Cu and P.Correlation coefficients higher than 0.7 are observed between abundances of Ti-Ce, Fe-Mn, Ti-V, Ce-V, Ca-Sr, Na-Ca, Na-Al and Fe-V. The Ti-Ce correlation is found to have originated from sphene, a Ti-bearing mineral. The Fe-Mn-V correlation is considered to have come from iron oxides and Fe-Mn deposit in river bottoms. The correlation among Ca-Sr-Na may reflect compositional variations in a rock-forming mineral, plagioclase. A clear distinction of a dispersed element by human activities in the natural background is the fundamentals for environmental assessment. The geochemical map is found to be a potentially important tool to clarify various sources of elements distributed in the geosphere., 国立情報学研究所で電子化したコンテンツを使用している。