GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
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Volume 55, Issue 5
Displaying 1-4 of 4 articles from this issue
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  • Combined tracers in hot spring waters across the Kii Peninsula, Japan: Implications for the origins of metamorphic fluids of the SW Japan forearc
    Koki Momose, Makoto Shiogama, Masako Hori, Kazuhiko Kandori, Yoshiro N ...
    Article type: research-article
    2021 Volume 55 Issue 5 Pages 289-300
    Published: 2021
    Released on J-STAGE: November 22, 2021
    DOIhttps://doi.org/10.2343/geochemj.2.0637
    JOURNAL FREE ACCESS
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    Spring waters from 16 sites distributed across the Kii Peninsula and surrounding islands in SW Japan were studied, to understand the origins of the metamorphic fluid; they were first classified into five types, based on a Piper diagram. Spring waters enriched in Na-K-HCO3 (referred to as type IV) exhibited rare earth element patterns with strong positive Eu/Eu* anomalies, evidencing significant influence of plagioclase decomposition. Type IV samples were generally from inland sites, with relatively low Cl concentrations, while their total ion concentrations tended to increase as their Li/B ratios increased. Most of samples enriched in Na-K-Cl, distributed on the western side of the peninsula, were explained by the mixing of seawater with type IV groundwater. Some non-meteoric, δD-δ18O signatures detected in these samples may have been produced by clay mineral dehydration in the pelitic schist of the Sambagawa metamorphic zone, and not necessarily by slab-derived fluid. We also found one exceptional sample, which was enriched in Ca-Mg-Cl, and had a high Cl proportion without seawater mixing, which suggested the contribution of dehydrated fluid from Cl-enriched serpentinite.
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  • Constraints of the geochemical characteristics of apatite on uranium mineralization in a uraninite-rich quartz vein in the Haita area of the Kangdian region, China
    Minghui Yin, Zhengqi Xu, Hao Song, Chengjiang Zhang, Suheng Zhang, Jia ...
    Article type: research-article
    2021 Volume 55 Issue 5 Pages 301-312
    Published: 2021
    Released on J-STAGE: November 22, 2021
    DOIhttps://doi.org/10.2343/geochemj.2.0638
    JOURNAL FREE ACCESS
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    Uraninite is commonly smaller than 1 mm and widespread in felsic or alkaline igneous rocks as accessory minerals. However, abundant coarse-grained euhedral uraninites, up to 1 cm in size, are intergrown with sphene, apatite, zircon, and some other accessory minerals in a quartz vein from the Haita area of the Kangdian region, China. Although previous studies have examined uraninite in detail, the genesis of the uraninite-rich quartz vein remains controversial. In this study, we investigate the relationships among euhedral single-particle apatite (ApA), aggregated apatite (ApB), and uraninite in a uraninite-rich quartz vein. TESCAN integrated mineral analysis, electron probe microanalysis, and laser ablation inductively coupled plasma mass spectrometry were used to investigate the nature of the ore-forming fluids of U mineralization. The two types of apatites have similar major element compositions and rare earth element patterns, whereas trace elements, such as Mn, U, and Cu, exhibit different characteristics, indicating a two-stage evolution of the ore-forming fluids. In addition, both types of apatite are fluorapatite, indicating high F concentrations in the ore-forming fluid, which favors U mobility. Changes in the concentrations of multivalent elements (such as Mn, Eu, and Ce) in the two types of apatite indicate that a slow increase in the oxygen fugacity promotes megacrystalline uraninite formation. A significant increase in the U concentrations from ∼46.56 ppm in the ApA to ∼7,169.12 ppm in the ApB likely represent an enrichment of U in the fluid. This study provides a new geochemical basis for understanding the mechanism of megacrystalline uraninite formation.
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  • Seasonal variation of monoterpene emissions from forest floor and its contribution to whole canopy flux in a Larix kaempferi forest
    Tomoki Mochizuki, Moeko Ujihara, Yoshiyuki Takahashi, Hajime Kobayashi ...
    Article type: research-article
    2021 Volume 55 Issue 5 Pages 313-324
    Published: 2021
    Released on J-STAGE: November 22, 2021
    DOIhttps://doi.org/10.2343/geochemj.2.0640
    JOURNAL FREE ACCESS
    Supplementary material
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    To understand monoterpene emission from a deciduous coniferous forest floor, we measured monoterpene emission rate of the forest floor and monoterpene content in needle litter in a Larix kaempferi forest, Japan in spring, rainy season, summer, and late autumn. Six soil chambers were set up on the L. kaempferi forest floor, and experimental plots were left undisturbed (no removal of needle litter and fine roots). The dominant compound in all seasons was α-pinene. The monoterpene emission rate from the forest floor depended on temperature. The highest standard monoterpene emission rate (at 21°C) from the forest floor was observed in late autumn, and the lowest occurred in summer. The seasonality of standard monoterpene emission rates was similar to that of monoterpene content in the needle litter. We calculated the ratio of monoterpene emissions from the forest floor to canopy scale monoterpene fluxes. The highest ratio was observed in late autumn (28%), whereas the lowest ratio was observed in summer (0.07%). Our results suggest that the forest floor of a deciduous coniferous L. kaempferi forest is an important source of monoterpene emission in autumn, and the contribution of forest-floor monoterpene emissions to canopy-scale monoterpene flux depends on the season.
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  • Shorter average chain length of n-alkanes from flowers than leaves of modern plants: Implications for the use of n-alkane-derived proxies in soils
    Yue Fang, Jing Yang, Shijing Zhao, Jie Wu, Yuying Huang, Huan Yang
    Article type: research-article
    2021 Volume 55 Issue 5 Pages e19-e23
    Published: 2021
    Released on J-STAGE: November 22, 2021
    DOIhttps://doi.org/10.2343/geochemj.2.0639
    JOURNAL FREE ACCESS
    Supplementary material
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    The average chain length (ACL) of leaf wax n-alkanes has been widely used to differentiate plant types and to reconstruct the paleoenvironment. However, it is still unclear whether or not the ACL differs significantly between different plant organs, in particular between flowers and leaves. Here, we collected flower and leaf samples from 18 plant species and compared the distribution of n-alkanes and n-alkane derived proxies. The abundance and distribution of n-alkanes from flowers differed remarkably from those of leaves. Flowers could produce high concentrations of n-alkanes, with the most abundant compound (Cmax) for flowers being lower than or equal to that for leaves. The ACL values of flower n-alkane for all plant species were lower than those of leaf n-alkane. This suggests that the contributions of flower n-alkanes to soils need to be evaluated before n-alkanes are used for paleoclimate reconstruction.
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