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Watanabe, Takahiro; Kokubu, Yoko; Murakami, Hiroaki; Yokoyama, Tatsunori; Amamiya, Hiroki; Mizuno, Takashi; Kubota, Mitsuru; Iwatsuki, Teruki
no journal, ,
Chronological and geochemical studies of fracture filling calcite in rocks provide the information for changes in geochemical condition, such as redox potential and pH in geological environments. Because the calcite can be found as common filling minerals in the natural samples, age zoning and spatial distribution of chemical composition in the calcite could be a wide-use indicator to reconstruct the past environmental changes. Radiometric (U-Pb) dating in a micro scale area (less than 10 micrometer) on the filling mineral surface by laser ablation-inductively coupled plasm mass spectrometry system (LA-ICPMS) has been applied to geological samples. Additionally, past redox potential has been estimated by Fe contents in the carbonates, which is based on the distribution coefficient of Fe between calcite deposit and groundwater. In this study, we evaluated the possibility of in-situ radiometric dating for the filling minerals by LA-ICPMS and redox potential reconstruction by the theoretical calculation using the distribution coefficient.
Yokoyama, Tatsunori; Mitsuguchi, Takehiro; Sueoka, Shigeru
no journal, ,
In recent years, it has become possible to carry out high-precision microscale age dating of geological samples using developed micro-analytical techniques such as SIMS, LA-ICP-MS, etc. Application of LA-ICP-MS-based microscale U-Pb dating is extending from U-rich heavy minerals such as zircon, apatite and monazite to U-depleted minerals such as calcite. This kind of method enables age determination of several types of mineral grains occurring within rock bodies, and thereby reveals chronological changes in chemical composition of source materials from which the minerals were crystallized, with some cases in which thermal history of the crystal formation system can be reconstructed. For research and development of geological disposal techniques for high-level radioactive wastes, we develop and facilitate geochronological dating techniques for evaluation of long-term stability in geological environments, at Tono Geoscience Center, Japan Atomic Energy Agency. In our presentation, we introduce the current status of our development for research on long-term stability of geological environments, U-Pb dating of calcite, U-Pb dating of young zircon and trace element analysis by using LA-ICP-MS.