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Yokoyama, Tatsunori; Kokubu, Yoko; Murakami, Hiroaki; Hirata, Takafumi*; Sakata, Shuhei*; Danhara, Toru*; Iwano, Hideki*; Chang, Q.*; Kimura, Junichi*
no journal, ,
The chronological information about carbonates is useful for modeling and enables forecast of geological and geochemical environmental changes by simulating. The U-Th-Pb dating method for carbonates which were formed at reducing environment remain to be established. The final goal of our study is to establish in situ U-Th-Pb dating method for carbonates which are filling cracks in pervious rock like fault rocks. In this study, the U-Th-Pb elemental and isotopic two-dimension distribution for an ammonite fossil were visualized by "Imaging" method using Laser-ablation ICP Mass Spectrometry. In U-Pb isotope analysis for carbonates in cracks of granites, we could not obtain significant U-Pb age data by the lack of uranium and influence of non-radiogenic common lead. When the concentration of lead is sufficiently high for the measurement, we obtained reliable isotopic data from carbonates and their lead isotopic composition reflected characteristic composition of their origin water.
Yokoyama, Tatsunori; Kokubu, Yoko; Murakami, Hiroaki; Watanabe, Takahiro; Hirata, Takafumi*; Sakata, Shuhei*; Danhara, Toru*; Iwano, Hideki*; Maruyama, Seiji*; Miyazaki, Takashi*; et al.
no journal, ,
Chronological and geochemical studies of carbonates, which are commonly found as fracture filling minerals in rocks, can provide information about geochemical conditions present during formation including in deep subsurface environments. A dating technique for the carbonates using laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) is still immature partly because of a lack of a consensus international carbonate standard for the in-situ dating technique. In this study, we performed a survey on the carbonate standard materials that may be suitable for high precision U-Th-Pb dating using LA-MC-ICPMS. We examined carbonate standard materials JCp-1 and JCt-1 issued by the Geological Survey of Japan (GSJ). Based on solution-based bulk analysis using MC-ICP-MS, heterogeneities in Pb isotope compositions were confirmed. Nevertheless, the 206Pb-based isotopic compositions were all within 1.2 per mill variations acceptable for a standard used for age determination using LA-MC-ICPMS. Additional tests on the heterogenities in U-Th-Pb compositions of the carbonate standards along with determinations of other trace elements using a 2D imaging LA-ICP-MS are ongoing. Examinations on both natural standards and synthetic standards are ongoing for further efforts in determination of the standard suitable for U-Th-Pb dating of carbonates.
Yokoyama, Tatsunori; Kokubu, Yoko; Murakami, Hiroaki; Watanabe, Takahiro; Mitsuguchi, Takehiro
no journal, ,
no abstracts in English
Yokoyama, Tatsunori
no journal, ,
no abstracts in English
Ogata, Nobuhisa
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The overview of geochronology at Toki Research Institute of Isotope Geology and Geochronology are given lectures as the invited lectures of the 128th lecture of the Japan Geodetic Society.
Shimada, Koji
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This report describes the current status of the development of dating technology at the Tono Geoscience Center, provides an overview of the significance of dating, and a framework of dating techniques, and highlights some of the achievements and current challenges.