GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
52 巻 , 6 号
選択された号の論文の9件中1~9を表示しています
  • Jiemei Lü, Yanling An, Qixin Wu, SHaoqi Zhou, Yonggui Wu
    2018 年 52 巻 6 号 p. 441-456
    発行日: 2018年
    公開日: 2018/12/05
    ジャーナル 認証あり

    Water samples were collected and analyzed for major ions in the dry season and wet season in the Qingshuijiang River Basin, to understand ion compositions and solute fluxes as related to rock weathering and associated CO2 consumption rates. The total dissolved solids (TDS) varied from 35.29 to 740.90 mg·L–1, and the mean value (217.5 mg·L–1) was significantly higher than the global rivers. Ca2+ and HCO3, dominated the ionic composition, accounting for approximately 61.95% of the total ionic budgets. TDS and major element concentrations decreased from the upstream to the downstream. Correlation and spatial distribution analysis showed that anthropogenic activities had a significant effect on water chemistry, probably contributed some 4.87% of the dissolved solutes. The chemical weathering rates were estimated to be 65.43 t·(km2·a)–1 (55.01 t·(km2·a)–1 and 10.42 t·(km2·a)–1 by carbonate and silicate weathering, respectively), comparable to the Changjiang River in China, but significantly higher than the average of world rivers. Atmospheric CO2 consumption rates by rock weathering within the basin was 72.57 × 104 mol·(km2·a)–1, 2.95 times the global average. Furthermore, the atmospheric CO2 consumption by the rock weathering was estimated to be 12.45 × 109 mol·a–1 (7.86 × 109 mol·a–1 by carbonate weathering and 4.59 × 109 mol·a–1 by silicate weathering, respectively), accounting for 0.11% of the global total consumption fluxes. The CO2 consumed by rock chemical weathering in the Qingshuijiang River Basin may constitute a significant part of the global carbon budget due to the intense CO2 consumption even though with the small area in the world.

  • Akizumi Ishida, Mizuho Koike, Naoto Takahata, Takuya Morita, Jean Davi ...
    2018 年 52 巻 6 号 p. 457-466
    発行日: 2018年
    公開日: 2018/12/05
    ジャーナル 認証あり

    A novel study of in situ hydrogen isotope composition (δD) measurements of micron-scale apatite inclusions hosted in zircon crystals was carried out by lateral high-resolution secondary ion mass spectrometry. The host rock of zircon is a tonalite belonging to the Nuvvuagittuq Supracrustal belt, Canada, which is considered to be one of the oldest supracrustal belts of Hadean-Archean age. Uranium-lead dating of host zircon crystals yielded an age of 3636 ± 20 Ma, which is consistent with previously reported ages of this unit. The δD values were measured for seven apatite inclusions, and range from –225 to +65‰ (vs. SMOW). A negative correlation was observed between δD values and the 18O/1H ratios of the examined apatite inclusions. This relationship can be explained by a mixing trend between the original hydrogen in the apatite inclusions and contamination from the analytical environment. The pristine δD value estimated for the apatite inclusion is +53 ± 60‰, which was clearly distinct from the δD value resulting from bulk rock analysis, –49 ± 2‰. The pristine δD value of the tonalitic magma source may provide new constraints on the formation of the primitive crust and/or the ocean of the early Earth.

  • Aratz Beranoaguirre, Christian Pin, Maria Eugenia Sanchez-Lorda, Julie ...
    2018 年 52 巻 6 号 p. 467-481
    発行日: 2018年
    公開日: 2018/12/05
    ジャーナル 認証あり

    A robust method is described allowing the sequential separation of Hf and the lanthanides from matrix elements of silicate rocks or minerals. This is based on a single chromatographic column filled with the conventional cation-exchange DowexAG50W-X8 resin, and hydrochloric, nitric and sulfuric acids as eluting agents. Samples can be processed following the same column protocol, irrespective whether they were decomposed by high temperature fusion with LiBO2 (ensuring a thorough sample/tracer isotopic equilibration in the molten glass, in case the isotope dilution method is used), or by hydrofluoric acid dissolution. The hafnium fraction separated in this way is ready for isotope ratio measurements by MC-ICP-MS, while the REEs are further processed by extraction chromatography for isolating Nd, Sm, and Lu, in view of TIMS and MC-ICP-MS analyses. The precision and accuracy of the method were evaluated by repeat analyses of four geological Reference Materials covering a range of silicate rock compositions.

  • Lin Xu, Chongguang Luo, Hanjie Wen, Zhengbing Zhou, Chaojian Qin
    2018 年 52 巻 6 号 p. 483-496
    発行日: 2018年
    公開日: 2018/12/05
    ジャーナル 認証あり

    In this study, fluid inclusion leachates, extracted from gangue quartz that is associated with ore minerals, are used to measure elemental components and Li isotopic compositions to investigate the sources of the ore-forming fluids of Zn-Pb-(Cu) deposits in the Jinbao mine district, the origins of which are still in controversy. Major components of the fluid inclusions are chloride-(Na,Ca). Interestingly, the elemental correlation (Na/Ba vs. Cl/Ba and Ca/Ba vs. Cl/Ba) shows that four deposits we investigated in the Jinbao mine district share common components in sources. The Li and its isotopic signatures (Li: 92.2 to 587.4 ng/L and the majority of δ7Li values: <+10‰) indicate that the ore-forming fluids in the Jinbao mine district may be originated from concealed granite magma. The δ7Li values of >+12‰, obviously higher than reported Li-rich peraluminous magma, are interpreted to be derived from the isotopic fractionation during fluid exsolution and the mixture between magmatic fluids and other fluids with higher δ7Li values. This study proves that Li isotopes could be a useful tool to track the sources of ore-forming fluids in Zn-Pb deposits.

  • Jong-Ku Gal, Jung-Hyun Kim, Daun Kim, Sujin Kang, Kyung-Hoon Shin
    2018 年 52 巻 6 号 p. 497-507
    発行日: 2018年
    公開日: 2018/12/05
    ジャーナル 認証あり

    In this study, we evaluated the saponification effect on alkenone quantification and the U37 paleothermometer using two internal standards (2-nonadecanone and squalane) by analyzing in-house reference sediment and eleven surface sediments taken from the Yellow Sea. The C37:3 and C37:2 alkenone concentrations of the in-house reference sediment showed significant differences between before and after the saponification (ΔC37:3 and ΔC37:2) depending on the internal standards used. However, the differences in the U37 and the estimated sea surface temperatures were insignificant. The ΔC37:3 and ΔC37:2 concentrations were larger when calculating based on 2-nonadecanone (46 ± 26 and 136 ± 67 ng/g, respectively) than those based on squalane (–7 ± 4 and –12 ± 10 ng/g, respectively) in the surface sediments. Interestingly, the ΔC37:3 and ΔC37:2 concentrations based on 2-nonadecanone showed a strong correlation with the loss of 2-nonadecanone that occurred during saponification. Accordingly, our study indicated that preferential loss of internal standards (e.g., 2-nonadecanone) can occur during saponification, which affects alkenone quantification and, thus, attention should be paid when choosing an internal standard.

  • Shuaimin Huang, Masaki Enami, Motohiro Tsuboi, Yuki Wakasugi
    2018 年 52 巻 6 号 p. 509-529
    発行日: 2018年
    公開日: 2018/12/05
    ジャーナル 認証あり

    The Tonaru epidote-amphibolite is one of the large metagabbro dominated bodies occurring in schistose lithologies of the Sanbagawa metamorphic belt, central Shikoku. Major and trace elements, including rare earth elements (REEs), in the Tonaru epidote-amphibolite and surrounding basic and pelitic schists along the Kokuryo River in the Besshi region of central Shikoku have been systematically investigated, and material interactions at their lithologic boundaries are discussed. Most parts of the Tonaru epidote-amphibolite have petrographic and chemical features similar to other epidote-amphibolites and eclogites in the Besshi region, which are dominantly metagabbro. In contrast, the epidote-amphibolites collected from the southern margin of the Tonaru body trend toward SiO2-rich compositions. Some of them show intermediate compositions between the basic igneous and pelitic lithologies in the SiO2-FeO*/MgO, Al2O3-CaO/(CaO + Na2O + K2O), Ti/100-Zr-Sr/2, and V-Ba systems, and have light REE-enriched patterns similar to sedimentary lithologies. Mafic and Al2O3-poorer samples are sometimes richer in Cr and Ni. These data suggest that the protoliths of the Tonaru epidote-amphibolites can be grouped into: (1) a gabbroic lithology; and (2) sedimentary mixtures of mafic, ultramafic and/or pelitic materials, likely derived from an oceanic island arc. There is no apparent compositional modification detected at a shear zone of 1.5–2.5 m width that developed at the northern boundary between the Tonaru epidote-amphibolite and pelitic schists. This feature implies that lithological mixing at this boundary was relatively insignificant during metamorphism and might not have effectively altered compositions of the metamorphic rocks without element transport promoted by circulating metamorphic fluids.

  • Tatsunori Yokoyama, Jun-ichi Kimura, Takehiro Mitsuguchi, Toru Danhara ...
    2018 年 52 巻 6 号 p. 531-540
    発行日: 2018年
    公開日: 2018/12/05
    ジャーナル 認証あり

    We developed a non-matrix matched U-Pb dating method for calcite by using excimer laser ablation-multiple Faraday collector-inductively coupled plasma-mass spectrometry (LA-MFC-ICP-MS). The excimer LA was set to generate a low-aspect-ratio crater of 100 μm diameter × 50 μm depth to minimize downhole U-Pb fractionation. We used He sample ablation gas mixed with Ar carrier gas and additional trace N2 gas to create a robust plasma setup in MFC-ICP-MS. The use of N2 additional gas allowed for low oxide molecular yield (UO+/U+ < 1%) for high-sensitivity JET-sampler and X-skimmer interface cones with the ICP shield electrode disconnected. Moreover, this resulted in robust ICP plasma against different matrixes in LA aerosols owing to efficient dissociation-ionization of the aerosols by increased plasma temperature. The above setup helped accomplish accurate U-Pb dating of calcite samples by using SRM 612 glass from the National Institute of Standards and Technology (NIST) as the standard. We applied this method to the following calcite samples: (1) recently-proposed reference material named WC-1 with a determined U-Pb age of 254.6 ± 3.2 Ma and (2) a well-preserved fossil specimen of blastoid Pentremites sp. with an estimated age of ~339–318 Ma. Prior to the U-Pb dating, quantitative two-dimensional maps of U, Th, and Pb isotope abundances of the calcite samples were obtained using a LA-ICP-MS imaging technique to select suitable areas for dating. Obtained U-Pb age of the WC-1 sample was 260.0 ± 6.7 Ma with an anchored point of initial 207Pb/206Pb ratio of 0.85 ± 0.02 determined by Roberts et al. (2017), which was close to the reported U-Pb age of 254.4 ± 0.8 Ma. The regression-based U-Pb discordant line age of the Pentremites sample was dated 332 ± 12 Ma, which indicate accurate U-Pb dating by this method.

Express Letters
  • Ryu Uemura, Miki Uemura, Masaki Sano, Takeshi Nakatsuka
    2018 年 52 巻 6 号 p. e21-e27
    発行日: 2018年
    公開日: 2018/12/05
    ジャーナル 認証あり

    The oxygen isotope ratio (δ18O) of tree-ring cellulose provides a valuable climatic record with an annual timescale. In Japan, the cellulose δ18O records have been accumulated over the past decade. However, no long-term records have been reported for the southern subtropical island, Okinawa-jima, where many long-lived trees were burned during the Second World War and have been periodically damaged by typhoons. Here, we show a cellulose δ18O of Ryukyu Pine (Pinus luchuensis Mayr.) from the Okinawa-jima island. This δ18O data, which was obtained from a tree-disk preserved in a University Museum, cover a 95-year period before meteorological observation began on this island in 1891. The cellulose δ18O variations negatively correlate with the amount of precipitation during the rainy season, suggesting that the cellulose δ18O values are largely affected by δ18O of rainwater rather than large scale ENSO variations.

  • Taejin Kim, Hajime Obata, Shigenobu Takeda, Kuo Hong Wong, Asami Suzuk ...
    2018 年 52 巻 6 号 p. e29-e38
    発行日: 2018年
    公開日: 2018/12/05
    ジャーナル 認証あり

    Distributions of trace metals (Mn, Fe, Cu, and Zn) and Zn chemical speciation were determined in Tachibana Bay to investigate the role of organic complexing ligands and sulfide on Zn in a coastal hydrothermal system. At the coastal area near Obama Hot Springs, dissolved sulfide was only detected in two bottom water samples in Stn. 6 (29.2 and 59.4 nM). At this coastal area, dissolved Mn and Fe concentrations were high and increased toward the bottom, whereas dissolved Cu and Zn concentrations generally decreased toward the bottom. The Zn complexing organic ligands (CL) and conditional stability constants (log KʹZnL,Zn2+) in Tachibana Bay ranged from 0.9 nM to 1.6 nM and from 9.9 to 10.3, respectively. The free sulfide concentration calculated from Zn chemical speciation was much lower than the measured dissolved sulfide concentrations. Although dissolved Zn mainly precipitate as sulfide in shallow hydrothermally active area, the organic complexation of Zn is important in the remaining dissolved Zn.

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