GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
最新号
選択された号の論文の4件中1~4を表示しています
  • Aftab Alam, Nanping Wang, Guofeng Zhao, Tahir Mehmood, Dimitrios Nikol ...
    原稿種別: research-article
    2019 年 53 巻 6 号 p. 341-358
    発行日: 2019年
    公開日: 2019/12/20
    ジャーナル 認証あり

    This paper reports chaos and long-memory trends hidden in radon (222Rn) variations in the groundwater of Panzhihua, Sichuan Province, China, between 2012 and 2017. The analysis is performed using sliding-window (a) detrended fluctuation analysis (DFA), (b) fractal dimension analysis with the methods of Higuchi, Katz and Sevcik and (c) residual radon concentration (RRC). Several fractional Brownian motion (fBm) persistent time series segments of high predictability are found, with DFA slopes above 1.5 and fractal dimensions, below 1.5. Numerous seven-day segments exhibit RRC out of the ±2σ limits and are of noteworthy precursory value. Through a novel two-stage computational approach, the persistent pre-seismic fBm earthquake footprint segments are separated from the low-predictability ones. Several combined segments of dynamical complexity are found with fractal and long-memory behaviour. For these segments, associations are attempted with major (Mw ≥ 6.0) earthquakes occurred in China and border areas of near countries during the period of study. Out of seventeen earthquakes of the period, four earthquakes are identified with all combinations of methods, whereas the remaining earthquakes, with the combination of at least three methods. Trends of long-memory are identified and discussed. The findings are compatible with fractal, and SOC final phases of generation of earthquakes. Finally, potential geological sources are discussed and analysed.

  • Xiaofeng Gao, Peixi Xiao, Lei Kang, Rengang Xi, Ping Li, Xianfeng Zha
    原稿種別: research-article
    2019 年 53 巻 6 号 p. 359-378
    発行日: 2019年
    公開日: 2019/12/20
    ジャーナル 認証あり

    The North Altyn Tagh subduction-accretionary belt (NASB), in NW China, contains Paleozoic ophiolitic suites, tectonic mélanges, and accretionary and metamorphic complexes related to the tectonic evolution of the Hongliugou-Lapeiquan Ocean. These assemblages represent the key to reveal the tectonic evolution of the southeastern margin of the Tarim Craton. New zircon U-Pb dating results indicate the eruption of the Hongliugou basalts in the late Ordovician. These basalts have depleted mantle-like radiogenic Nd (εNd(t) = +6.2~+6.7) and moderately radiogenic Sr isotopic compositions (87Sr/86Sr (i) = 0.7065–0.7068). They also have normalized trace element patterns between N-MORB and E-MORB. The combined geochemical data indicate their derivation from a moderately depleted mantle source enriched by fluids released from subducted sediments in a back-arc environment. Considering the widespread distribution of contemporaneous mafic rocks in the NASB, which show REE patterns lying between E-MORBs and N-MORBs, it is proposed that the Hongliugou-Lapeiquan Ocean remained active in the late Ordovician. The tectonic history of the Hongliugou-Lapeiquan Ocean was longer and more complex than previously recognized. It initially evolved as a marginal oceanic basin during the Cambrian and then began to close through slab subduction at ca. 510 Ma. Before the final closure at 440–410 Ma, the oceanic crust creation was renewed from ca. 460 to ca. 440 Ma in a back-arc setting.

  • Yan Fan, Shen Liu, Caixia Feng, Ian M. Coulson, Liang Liu, Chao Wang
    原稿種別: research-article
    2019 年 53 巻 6 号 p. 379-406
    発行日: 2019年
    公開日: 2019/12/20
    ジャーナル 認証あり

    The Altyn Orogenic belt is located in the northern margin of the Tibetan Plateau and its geodynamic setting during the early Neoproterozoic is poorly understood. Herein, we present the origin and geodynamic background of a suite of Neoproterozoic granitoids distributed in South Altyn. Representative samples of two-mica, muscovite, and biotite granites in the western region of the South Altyn Terrane, and granodiorite in the middle region were examined. The crystallization age of the two-mica granite is 948 ± 5.3 Ma, while the ages of the muscovite and biotite granites are 944 ± 7.3 Ma and 960 ± 4.5 Ma, respectively, and that of the granodiorite is 944 ± 4.4 Ma. These intrusions are all characterized by enrichment in large ion lithophile elements, as well as depletion in high field strength elements, high (87Sr/86Sr)i, (208Pb/204Pb)i, (207Pb/204Pb)i and (206Pb/204Pb)i ratios, negative εNd (t), and significant εHf (t) values ranging from –2.0 to 1.9. The corresponding two-stage model age (TDM2) values range from 1,673 Ma to 1,928 Ma. These results suggest that these granitoids were sourced from the partial melting of Paleoproterozoic crust, with a negligible contribution of mantle material. During the process of magmatic evolution of the two-mica granite, fractional crystallization of plagioclase and potassium feldspar was dominant, whereas fractional crystallization of amphibole and biotite features in the magmatic evolution of biotite granite, and fractional crystallization of pyroxene, amphibole, plagioclase, and rutile occurred during the magmatic evolution of granodiorite. Moreover, it is shown that the two-mica granite and muscovite granite belong to syn-collisional granite, while granodiorite and biotite granite belong to volcanic arc granite, which are related to an active continental margin. In view of this and previous studies, we favor the conclusion that the west part of the South Altyn Terrane was in a transitional period between pre-collisional and syn-collisional tectonics during the period 944–960 Ma. Nevertheless, the middle region was in the pre-collisional tectonics over a period of 944 Ma, which implies that the convergence in the western part of the South Altyn Terrane occurred earlier than in the middle region.

  • Yuki Nakaya, Satoru Nakashima, Takahiro Otsuka
    原稿種別: research-article
    2019 年 53 巻 6 号 p. 407-414
    発行日: 2019年
    公開日: 2019/12/20
    ジャーナル 認証あり

    Hydrothermal decolorization (color loss) of Nordic fulvic and humic acid solutions at 80–180°C for 0–600 hours was traced by ultraviolet-visible (UV-Vis) spectroscopy. These changes were considered to be due to degradation of humic-like chemical structure and represented by decreases in absorbance at 254 nm (UV254). The temperature dependence of their apparent rate constants obtained by the first order reaction model was well described by the Arrhenius equation giving activation energies of 87.6 and 101 kJ mol–1 for degradation of fulvic and humic acids, respectively. The degradation rates of humic substances were slower than the formation rates of humic-like substances by the Maillard-type browning reaction, suggesting that humic-like substances can be preserved in the aquatic environments, where their formation (browning) and degradation (decolorization) processes are occurring together. By extrapolation to 15°C of the Arrhenius equation, 99–1980 years of time scales for these processes were estimated. A time scale of changes in UV254 in natural aquatic environments estimated by kinetic analyses on Ago Bay bottom sediments (18 years) were closer to the formation time scales of humic-like substances.

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