In our earlier work, we determined relative REE partition coefficients between calcite and aqueous (CaCl₂ + NaCl) solution, but absolute values could not be obtained because of small overgrowths of calcite. In this study, we have made similar experiments in order to determine the absolute REE partition coefficients between calcite and aqueous solution, and have evaluated partition coefficients between calcite and seawater. Calcite-supersaturated solution doped with REEs was constantly pumped into a reactor to form calcite overgrowths on the seeds under CO₂ + N₂ gas. Absolute values of REE partition coefficients, K_d(REE)=(X_REE/X_Ca)_calcite/([REE,_tot.]/[Ca])_solution, have been obtained. The patterns of K_d(REE) show convex tetrad effects and Y/Ho fractionation, which is consistent with our earlier work. We have calculated REE abundances in Permian seawater using the partition coefficients corrected to seawater compositions and REE analyses of Permian seamount-type limestones. All the estimated REE abundances in Permian seawater indicate concave tetrad effects, large Y/Ho fractionation and negative Ce and Eu anomalies in their chondrite-normalized patterns, which are quite similar to those for present-day seawater. The estimated REE abundances in Permian seawater, however, are lower than those in present-day seawater by approximately one order of magnitude. This suggests that significant parts of marine limestones could not incorporate seawater REEs after the permeability and porosity of the original biogenic carbonate sediments with low-REE contents had been reduced to certain critical levels.

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Leaching experiments with pyroxene and plagioclase minerals and whole-rock basalt and distilled water were performed to clarify rare earth element (REE) behavior during water-rock interactions. A system was developed to recover the leachate quickly under nearly neutral conditions (pH ∼6) with little re-precipitation or adsorption. The release ratios (amount of an element in the leachate from the minerals or rock relative to the amount in the original minerals or rock) of REE were comparable to those of Mg and Ca. Rare earth elements were easily leached. More heavy REE (HREE) than light REE (LREE) were leached from the plagioclase, and more LREE than HREE from the pyroxene. Very little europium was leached from the plagioclase. These release patterns show an inverse relationship with the elemental partition coefficient between the minerals and magma. The trends in the REE release ratios thus depend mostly on the compatibility of each element with the crystal structure of the mineral, rather than on chemical characteristics such as the solubility of the element itself. During the basalt-water interaction, a negative Eu anomaly in the leachate increased with time because Eu was initially leached from interstitial minor phases and later was dominantly from the plagioclase which is the major host mineral of Eu.

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Intermediate to felsic volcanic rocks of the Baiqi formation from the Lingqiu basin in the central part of North China Craton were studied. Single zircon U-Pb dating indicates that these volcanics formed at 125.8±3.0 Ma. Their Sr and Nd isotopic compositions (¹⁴³Nd/¹⁴⁴Nd = 0.51180-0.51182, ⁸⁷Sr/⁸⁶Sr = 0.7062-0.7063) fall in the range of the nearby late-Mesozoic basaltic rocks. These volcanics share geochemical affinities to the adakites formed in the modern arcs, e.g., high Na₂O (>4.06%), Al₂O₃ (>15.4%) and Sr (645-1389 ppm) contents and Sr/Y ratios (55∼103), and thus being termed as adakitic rocks. However, the Baiqi adakitic rocks were not temporospatially associated with active subduction. Furthermore, their low Cr (2.19-47.4 ppm, with average of 25) and Ni (1.57-20.7 ppm, with average of 12) contents and Mg# (22-47, with average of 32) argue against interaction with the lithospheric mantle. Combined with the geological setting, we suggest that the Baiqi adakitic rocks resulted from partial melting of a thickened lower continental crust associated two episodes of basaltic underplating events. We propose that enormous conductive heating from 80-140 Ma basaltic underplating resulted in partial melting of pre-existing mafic lower crust formed by ∼150-160 Ma basaltic underplating. This study provides a case for partial melting of the thickened lower continental crust in association with basaltic underplating events.

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Some major and trace elements in seawaters and related river waters from the Osaka Bay area, Japan were analyzed in order to examine rare earth element (REE) behaviors, especially the relationship between anthropogenic gadolinium (Gd) and nutrient concentrations. The local silicic rock normalized REE patterns for the seawaters show features of light REE depletion, negative Ce anomaly, and very small Eu anomaly. Moreover, some samples have obvious positive Gd anomalies due to contamination of Magnetic Resonance Imaging (MRI) contrast agents in medical use. We calculated the anthropogenic Gd concentrations by subtracting the assumed natural Gd concentration from the measured one. The anthropogenic or excess Gd concentrations of the seawater samples are well correlated with nutrient concentrations (NH₄-N, NO₂-N, NO₃-N, PO₄-P). Because both anthropogenic Gd and nutrients are abundant in sewage treatment plant (STP) effluents and much less abundant in non-contaminated river and seawaters, the observed trends can be explained by dilution of STP effluents with non-contaminated river and seawaters. It was found that the nutrient concentrations for a hypothetical STP effluent calculated by using these correlation lines are consistent with the average nutrient contents for the STP effluents in the study area. Moreover, we made a rough estimation of Gd budget in Osaka Bay. The estimated amount of the Gd MRI contrast agents consumed in the area seems to be consistent with the excess Gd concentrations of river and STP waters. The Gd observations in this study suggest that the Gd anomaly data can be used as a geochemical tracer of wastewater component in urban areas.

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Chemical and isotopic compositions of brines collected from the Minami-Kanto natural gas field in Chiba, central Japan, were measured to investigate their origin and relation to microbial methane formed from the coexisting brines. The isotopic compositions of water in the brines are -3.8 to -1.5‰ and -15 to -1‰ in δ¹⁸O_H2O and δD_H2O values, respectively, which are correlated with their chloride concentrations, suggesting that the brines are derived from seawater and that some of them have been mixed with meteoric water. The brines have high concentrations of iodine up to 0.14 g/l which are related to those of dissolved bromine and ammonia. These dissolved chemicals are suggested to have been liberated from marine sediments into pore water through the diagenetic decompositions of organic matter. The hydrogen isotopic compositions of methane (δD_CH4) in the natural gases are -195 to -146‰. The average isotopic difference between δD_CH4 and δD_H2O for the samples is about 180‰, suggesting that the methane was formed by microbial activity via a CO₂-reduction pathway. However, because the data obtained in this study were widely scattered on the δD_CH4-δD_H2O plot, it is not possible to confirm that the obtained data follow the linear correlation predicted by Schoell (1980) for methane formation by CO₂-reduction.

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Geochemical and isotopic studies were carried out on Paleocene mafic rocks in the Taihe Basin, central Jiangxi, Southeast China, in order better to understand their magma sources and tectonic implications. K-Ar dating results show that these mafic rocks intruded during the Paleocene (50-65 Ma). These Paleocene mafic rocks are porphyritic diabase and have similar geochemical features, such as strong enrichment of large ion lithophile element (LILE, e.g., Rb, Ba, Sr), slight enrichment of light rare earth element (LREE) and high field strength element (HFSE, e.g., Nb, Ta, Ti, P). The mafic rocks are also characterized by high rare earth element (REE) and minor Eu anomalies (δEu = 0.88-1.2) and have uniform initial ⁸⁷Sr/⁸⁶Sr (0.7041-0.7064) and Pb isotopic composition (²⁰⁶Pb/²⁰⁴Pb = 18.338-18.677) as well as a relatively wide range of initial Nd isotopic ratios (ε_Nd(T)) varying from +0.8 to +6.2. These geochemical characteristics are different from those of subduction-related basalts, but similar to oceanic island basalts (OIB). Geochemical and isotopic evidence suggests that mafic rocks in the Taihe Basin were not significantly affected by crustal contamination and originated from asthenospheric mantle with a minor involvement of EM 2 mantle component. It is noted that Cretaceous basaltic rocks in Southeast China show enriched geochemical and isotopic compositions and were derived from a highly heterogeneous lithospheric mantle with minor asthenosphere components. On the other hand, Late Cenozoic basalts in Southeast China, which display OIB-like geochemical characteristics, were probably generated by melting of depleted asthenospheric mantle (DMM or MORB) with an involvement of EM 2 lithospheric mantle and a paucity of EM 1 lithospheric mantle. The Paleocene mafic rocks of the Taihe Basin exhibit transitional geochemical features between Cretaceous and Late Cenozoic basaltic magmatism, indicating that the involvement of asthenospheric mantle beneath Southeast China increased with time from Late Mesozoic to Cenozoic. It is suggested that the lithosphere replacement beneath Southeast China was associated with lithosphere extension and thinning, with decompression melting of the upwelling asthenosphere having taken place during the Paleocene period. Lithosphere replacement might be related to subduction roll-back or/and steepening of Paleo-Pacific plate due to injection of asthenospheric material into the mantle wedge beneath Southeast China.

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To assess the role of impact related reheating on compositional trends in the major elements of the L chondrite parent(s), I examined a suite of 37 L falls analyzed by Jarosewich (1990). After eliminating 8 samples prepared from quantities which differently sampled the chondrites considered, I found that suites of mildly-shocked (S3) and strongly-shocked (S4-S6) equilibrated L chondrite falls can be distinguished at statistically significant levels when compared based on their major element content. Graphical comparisons demonstrated that the differences arise because siderophiles are depleted with corresponding mass-balanced lithophile enrichment in strongly-shocked samples. Since the samples considered here were derived from volumes of between 1.5 cm³ and 4.7 cm³, we can conclude that statistically significant post-metamorphic metal(sulfide)/silicate segregation occurred on a scale of at least this size.

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Sequential extraction was used to study the operationally determined chemical forms of Co, Cr, Cu, Ni, Pb and Zn and their spatial distribution in the sediments of the Tapi estuary. It was found that oxidizable binding fraction was the most important phase for binding of all metals followed by Fe-Mn oxide and carbonate fractions. Zn bound to the Fe-Mn oxide fraction had a significant relationship with reducible Mn and reducible Fe concentrations suggesting that Fe-Mn oxides may be the main carriers of Zn from the fluvial environment to the estuarine body. The Zn bound to the Fe-Mn oxides and Cu bound to the oxidizable fraction showed a general distinctive decrease from the middle of the estuary (ES-3) to sea mouth (ES-5) and from upstream ES-2 to the mouth of the estuary (ES-2). Zn, Pb, and Cr were not correlated with bottom layers and had a high enrichment factor (up to 60 times) representing the influence of anthropogenic activities and thus are the main precursors of metal pollution. The average I_geo of six metals in the sediments from the middle of the estuary is 3.67 and is larger than the estuary mouth (1.24) and seaside sampling locations (2.33). This suggests that the middle of the estuary is strongly contaminated with heavy metals. Interestingly higher enrichment in the sediments is not linearly related to toxicity response factor which may be due to metal immobilization.

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The geochemical characteristics of Archean unusual siliceous rocks at Mt. Goldsworthy region in the Pilbara Craton were studied. The siliceous rocks have been assigned to the uppermost Warrawoona Group mafic volcanic rocks, and are overlain by quartz-rich sandstone units of the Strelley Pool Chert that probably represent continental margin sedimentation. The Warrwoona rocks have been heavily altered and are now composed dominantly of microcrystalline quartz, with subordinate mica, Fe-Ti oxides and unidentified silicates; original magmatic textures are only locally preserved. The complex alteration is assumed to result from multiple events including weathering during subaerial exposure, circulation of hydrothermal fluids, and metasomatic silicification. During alteration, Al, Ti, Zr, Th, Cr and Sc remained immobile, although their concentrations were lowered by a substantial increase in silica. Mutual ratios of these immobile elements such as Al₂O₃/TiO₂ Cr/Th, Th/Sc, Cr/Al₂O₃ and Zr/TiO₂ and comparison with the least-altered contemporaneous mafic-ultramafic rocks in the Pilbara Craton show that the altered rocks originated from high-MgO rocks such as komatiite and high-MgO basalt, possibly of Al-depleted type. The Mt. Goldsworthy rocks have significantly higher Th/Sc (0.024-0.1) values compared with primitive mantle values (0.005) and komatiite (0.01). This feature is interpreted as a result of crustal contamination, which is consistent with the early evolution of continental crust.

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The U-Th radioactive disequilibrium measurements with Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) were applied to a coral reference; JCp-1 distributed by the Geological Survey of Japan to evaluate homogeneity of the standard material.
The two times of standard deviations (2SDs) of [²³⁵U/²³⁸U]_{isotope ratio}, [²³⁴U/²³⁸U]_{isotope ratio}, U abundance, [²³⁰Th/²³²Th]_{isotope ratio}, and Th abundance results for four repetitive measurements were 0.1%, 1%, 1%, 39%, 15%, respectively. Those of [²³⁴U/²³⁸U]_{isotope ratio} and U abundance analyses are slightly larger than the analytical reproducibility. Those of Th isotope and abundance analyses are, however, much larger than the analytical reproducibility, suggesting that U is relatively homogeneous in JCp-1, whereas Th is not.
Although JCp-1 was prepared from a living coral, the apparent U-Th disequilibrium ages range from 0.82 to 1.14 ka. Th abundances varied from 46 ppb to 56 ppb, which is significantly higher than ordinary coral. It is possible that the observed high Th abundance may have resulted from contamination during preparation steps for the rock powder. Or it may have caused by inclusion of sandy material during the growth of the coral. The presence of residue after nitric acid dissolution indicates the presence of non-carbonate component. The correction of the contribution of ²³⁰Th from the contaminant, however, still gives ages older than zero. In addition, [²³⁴U/²³⁸U]_{isotope ratio} of JCp-1 is higher than the value of present seawater, suggesting the coral may have experienced some diagenesis.

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