GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
48 巻 , 1 号
選択された号の論文の11件中1~11を表示しています
  • CHANGYUAN YU, JING ZHANG, XIAOLEI WU, YEQING LAN, LIXIANG ZHOU
    2014 年 48 巻 1 号 p. 1-7
    発行日: 2014/01/20
    公開日: 2014/02/05
    ジャーナル フリー
    Adsorption of Cr(VI) by biogenic schwertmannite in a continuous flow column was studied. The effects of flow rates, initial pH values, dosages of schwertmannite, and accompanying anions on Cr(VI) adsorption were investigated. The results demonstrated that the optimal flow rate and pH for Cr(VI) removal were 1 mL/min and 6, respectively. The maximum adsorption amount obtained in this study was 35.30 mg/g, demonstrating that the biogenic schwertmannite held a high adsorption capacity for Cr(VI). Removal of Cr(VI) by adsorption was hardly affected by common anions, except for H2PO4. Based on the results obtained in this study, a mechanism for Cr(VI) adsorption by biogenic schwertmannite was proposed using the anion exchange processes between various Cr(VI) species and SO42−, a constituent of schwertmannite.
  • HIDENAO HASEGAWA, NAOFUMI AKATA, HITOSHI KAWABATA, TADAHIRO SATO, YUKI ...
    2014 年 48 巻 1 号 p. 9-18
    発行日: 2014/01/20
    公開日: 2014/02/05
    ジャーナル フリー
    Characteristics of δ2H and δ18O in precipitation samples collected at 16- to 17-d intervals at three stations at the northern end of Honshu Island, Japan, were investigated. Rokkasho and Ajigasawa stations are approximately 100 km apart, on the Pacific Ocean coast and the Sea of Japan coast, respectively, of Aomori Prefecture. Hakkoda station is between Rokkasho and Ajigasawa stations at 1334 m ASL. Precipitation samples were continuously collected during 2000–2011 at Rokkasho, and during 2003–2006 at Ajigasawa and Hakkoda. At all stations, δ2H and δ18O of the precipitation samples showed weak seasonality, with higher values in summer and lower values in winter. In the summer (June, July, and August), the intercept of the regression line between δ2H and δ18O, that is, the local meteoric water line (LMWL), was lower than that of the global meteoric water line (GMWL) with similar slope, but in winter (December, January, and February), the LMWL intercept was higher than the GMWL intercept with similar slope. Temporal variations of δ18O at the two coastal stations were similar, although the timing of precipitation events was different. At all stations, d-excess values showed clear seasonality, with high values in winter and low values in summer, indicating a seasonal change in the source of the water vapor in air masses arriving over northeast Japan. In winter, d-excess values were higher at Hakkoda than at the other stations, suggesting a precipitation at Hakkoda was derived from water vapor from a remote area of the Sea of Japan. The long-term precipitation data set for δ2H and δ18O obtained in this study will be useful for investigations of regional hydrology and validation of numerical models.
  • XI-AN YANG, JIA-JUN LIU, SI-YU HAN, GUO-HAO JIANG, DE-GAO ZHAI
    2014 年 48 巻 1 号 p. 19-28
    発行日: 2014/01/20
    公開日: 2014/02/05
    ジャーナル フリー
    The Yangla copper deposit is located in western Yunnan Province, China, with an estimated Cu reserve of approximately 1.2 million tons. It is a typical giant copper deposit, and its mining started only recently. The δ13CV–PDB values of the calcites studied vary from −5.1‰ to 1.0‰, implying that the hydrothermal fluids from which the calcites precipitated were derived from the granitic magma. The δ18OSMOW(H2O) and δDSMOW values of quartz fluid inclusions range from 0.11‰ to 2.50‰ and from −120‰ to −100‰, respectively. These data may suggest the following: (1) mixing between meteoric and magmatic fluids, or (2) the evolution of meteoric fluid by its interaction with igneous or metamorphic rocks. The δ34S values of sulfides range from −4.20‰ to 1.85‰ (average: −0.85‰), which is consistent with the magmatic origin. Based on the 3He/4He ratios of fluid inclusions trapped in sulfides of the deposit (0.14–0.17 Ra) and 40Ar/36Ar ratios of 301–1053, it can be inferred that the ore-forming fluids of the deposit were derived primarily from the crust with a minor mantle component during the metallogenic processes. Based on C, H, O, and S isotopic compositions, and the Yangla copper deposit is bordered primarily by gently dipping thrust faults near the Linong granodiorite. Moreover, the 187Re–187Os isochron age of molybdenite puts the time of metallogenesis at 233.3 ± 3 Ma, which is virtually coeval with the emplacement of the Linong granodiorite (235.6–234.1 Ma) and highlights the genetic link between the Yangla copper deposit and the Linong granodiorite. It is likely that the ore-forming fluids exsolved from the Linong granodiorite, which was formed by crustal melting induced by the intrusion of mantle-derived magma. During the late Early Permian, the Jinshajiang oceanic plate was subducted to the west, resulting in the formation of a series of gently dipping thrust faults in the Jinshajiang tectonic belt. Subsequently, the thrust faults was tensional during the early Late Triassic, which was a time of transition from collision-related compression to extension in the Jinshajiang tectonic belt; such conditions produced an environment favorable for the formation of ore fluids. This extension, in turn, induced the upwelling of hot asthenosphere, triggering intense melting in the lithospheric mantle and producing voluminous basaltic magma. Subsequently, the mantle-derived magma likely ascended along the fractures and faults to underplate the lower crust, which underwent partial melting to generate voluminous granitic magma. After the magma reached the base of the early-stage Yangla granodiorite, the platy granodiorite at the base of the Yangla body shielded the late-stage magma. Then, this magma cooled slowly, releasing some of its ore-forming fluids into the gently dipping thrust faults near the Yangla granodiorite and producing mineralization.
  • MASAOKI UNO, HIKARU IWAMORI, HITOMI NAKAMURA, TETSUYA YOKOYAMA, TSUYOS ...
    2014 年 48 巻 1 号 p. 29-49
    発行日: 2014/01/20
    公開日: 2014/02/05
    ジャーナル フリー
    Trace element and Sr–Nd–Pb isotopic compositions of basic schists in the Cretaceous Sanbagawa metamorphic belt, a typical regional metamorphic belt in the circum-Pacific orogeny, have been investigated for constraining hydration processes based on the observations of thin-sections and outcrops. The basic schists have undergone significant hydration from 0.8 GPa, 550°C to 0.3 GPa, 400°C during decompression towards the surface at the final stage of metamorphism. High-field-strength and rare-earth element compositions of the basic schists, as well as the Sr–Nd–Pb isotopic ratios, are different among three mineral zones with different peak PT metamorphic conditions; the basic schists in the low-grade chlorite zone shows N-MORB-like compositions whereas those in the higher-grades, garnet and oligoclase–biotite zones, show more enriched compositions (E-MORB-like). On the other hand, there is a common feature to all the metamorphic zones; the enrichment degree of some group of elements (e.g., large-ion lithophile elements) relative to high-field-strength and heavy-rare-earth elements is proportional to loss on ignition that approximately measures the bulk rock H2O content. This correlation suggests that Li, B, K, Cr, Ni, Rb, Sr, Cs and Ba have been added to the basic schists during hydration. The addition of these elements amounts to as much as 60–80% of the bulk abundance, indicating that significant amounts of elements were transported via pervasive fluid flow, which overprinted the variation in the bulk rock compositions of the protolith. The estimated compositions of hydration fluid are dense in large-ion lithophile elements, lead and light-rare-earth elements (10–100 times denser than primitive mantle) and are similar to those of the slab-derived fluids that induce arc volcanism. These elements (Cs, Rb, Ba, K, La, Ce and Pb) are thought to have been preferentially partitioned into the fluid when it was generated at depth. Such high concentrations indicate a high temperature origin of the hydration fluid, and are consistent with a model of hot slab subduction during exhumation of the Sanbagawa belt.
  • HARUNA SUGAHARA, KOICHI MIMURA
    2014 年 48 巻 1 号 p. 51-62
    発行日: 2014/01/20
    公開日: 2014/02/05
    ジャーナル フリー
    We conducted shock experiments simulating comet impacts to assess the feasibility of peptide synthesis by such a process. We used frozen mixture of the amino acid glycine, water ice, and silicate (forsterite) as the starting material and applied impact shocks ranging from 4.8 to 26.3 GPa using a vertical propellant gun under cryogenic conditions (77 K). The results show that amino acid oligomerization up to trimers can be achieved. Further, linear peptides (dipeptide and tripeptide forms), which are important materials for the further elongation of peptide chains, were obtained in yields of one or two magnitudes greater than that of cyclic peptide form (diketopiperazine). These results contrast with those by Blank et al. (2001) for shock experiments of amino acid solutions at room temperature, which showed the synthesis of a comparable amount of diketopiperazines to that of the linear peptides. Thus, the existence of cryogenic conditions at the point of impact shock may be critical for the formation of linear peptides. Our results demonstrate that comet impacts could have supplied a significant amount of linear peptides on the early Earth and other extraterrestrial bodies.
  • JAVIER A. DÍAZ-OCHOA, SILVIO PANTOJA
    2014 年 48 巻 1 号 p. 63-71
    発行日: 2014/01/20
    公開日: 2014/02/05
    ジャーナル フリー
    The main input of phosphorus to the ocean is associated with river runoff, while this element leaves the marine system via burial in the sediments. Solid phase P accumulation is a function of bottom water and surface sediment oxygenation. Theory predicts that suboxic/anoxic sediments act as a source of phosphate, which is released from organic matter and iron oxides, while authigenic precipitation and biogenic apatite preservation are both favored in a phosphate saturated environment. In this paper, we present the results of solid phase phosphorus speciation in sediments collected in central south Chile on the continental shelf off Concepción. This area is characterized by very high biological productivity and the formation of a strong oxygen minimum zone during summer. We found that total solid phase P was dominated by inorganic phases (60%), mostly comprised by iron-bound P and biogenic apatite P. As expected, biogenic apatite P and iron-bound P were negatively correlated and reflected bottom water oxygen fluctuations during the period analyzed (February–September 2009). The biogenic apatite (fish debris) preservation potential was negatively correlated with bottom water dissolved oxygen and its burial averaged 16% of water column’s fish production estimated with a trophic dynamic-model that included SeaWIFS-MODIS satellite primary productivity estimations. In spite of intrusions of oxygen in the water column evidenced by the thinning of the oxygen minimum layer in autumn-winter, bottom waters remained suboxic during the studied period and appear to have favored biogenic apatite P (Pfish) preservation. This finding supports the potential of Pfish as a paleotracer for fish abundance in areas previously not considered because of the lack of laminated sediments.
  • MASAKO HORI, TSUYOSHI ISHIKAWA, KAZUYA NAGAISHI, CHEN-FENG YOU, KUO-FA ...
    2014 年 48 巻 1 号 p. 73-84
    発行日: 2014/01/20
    公開日: 2014/02/05
    ジャーナル フリー
    This study examines the distribution of rare earth elements (REEs) in an 18–4.5 ka stalagmite in southwestern Japan, with the aim of assessing the utility of such data in paleoenvironmental reconstructions. Shale-normalized REEs (REEN) of this stalagmite generally contain two features: (1) a positive Eu anomaly and (2) heavy REE (HREE) enrichments. The magnitude of the positive Eu anomaly is most likely controlled by the relative contribution of REEs from weathered wall-rock andesites, which is estimated to be 19–96% of the total REEs in the stalagmite. The HREE enrichments in the stalagmite are likely to have formed by ionic radii-dependent fractionation between mineral and aqueous phases, where parental waters for the stalagmite preferentially incorporated the HREEs with relatively low partition coefficients (DREE) during bedrock dissolution. In contrast, calcite precipitation causes quantitative incorporation of dissolved REEs by the stalagmite, all of which are highly compatible with calcite (DREE > 100). This indicates that stalagmite REE patterns should be identical to dripwater REE patterns. The REE characteristics of the stalagmite also changed temporally with the period of deglaciation (16.6–7.1 ka) that was associated with slow stalagmite growth rates, and this coincided with high LaN/NdN ratios (>1). La (and Ce) have effective ionic radii that are smaller than that of Ca2+ (100 pm), and these were enriched in aqueous phases during slow dissolution of the bedrock. The data presented here indicate that the stalagmite REE patterns may be useful as potential indices for local weathering intensity.
  • WATARU SATAKE, TAKASHI MIKOUCHI, MASAMICHI MIYAMOTO
    2014 年 48 巻 1 号 p. 85-98
    発行日: 2014/01/20
    公開日: 2014/02/05
    ジャーナル フリー
    We used synchrotron radiation Fe micro-XANES (X-ray Absorption Near Edge Structure) analysis to determine the iron valence of maskelynite (shocked-plagioclase glass) in thirteen shergottites, and we compared the Fe3+–Fe2+ peak-intensity ratios for maskelynite in the shergottites in order to compare the redox states of the shergottites and discuss the evolution of the Martian crust and mantle. We analyzed two geochemically depleted (Dar al Gani 476 and Dhofar 019), four geochemically intermediate (EETA 79001 lithology A, ALH 77005, LEW 88516, and NWA 5029), and seven geochemically enriched (NWA 856, Zagami, Shergotty, RBT 04262, NWA 4468, NWA 1068, and LAR 06319) shergottite samples. The Fe3+–Fe2+ peak-intensity ratios for maskelynite in the depleted, intermediate, and enriched shergottites were 0.39–0.49, 0.13–0.66, and 0.40–0.81, respectively. LAR 06319, NWA 856, NWA 1068, Zagami, and Shergotty, whose log fO2s were higher than QFM-2.0. RBT 04262 showed the highest Fe3+–Fe2+ peak-intensity ratios for maskelynite in the enriched shergottites; therefore, RBT 04262 might have crystallized under a more oxidized environment than the other enriched shergottites. Similarly, NWA 4468 was estimated to have crystallized at log fO2 higher than QFM-2.3. This is the first report showing that RBT 04262 and NWA 4468 are oxidized samples because no oxybarometer measurements had previously been performed on these samples. We showed that XANES analysis can be applied to any maskelynite-bearing samples in order to discuss the difference between the redox states of Martian meteorites. We also revealed that the Fe3+–Fe2+ peak-intensity ratios for maskelynite in the intermediate shergottites show a very wide range (0.13–0.66), exceeding the ratios obtained for maskelynite in the depleted and enriched shergottites. When previously reported geochemical characteristics such as the εNd and crystallization ages are included, the wide range of the Fe3+–Fe2+ peak-intensity ratios obtained for maskelynite in the intermediate shergottites does not support the model that proposes that two distinct mantle reservoirs mix during melting. The results of this study reveal that the redox state of the source of the enriched shergottites is heterogeneous.
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