5:15 PM - 6:30 PM
[HCG25-P06] Geosphere stability project (6) Chronological and chemical analyses of carbonate minerals
Keywords:carbonate minerals, radiometric dating, redox potential, LA-ICPMS, geosphere stability, geological disposal
(1) Radiometric dating by LA-ICPMS
In order to develop high spatial resolution dating of the filling minerals, we should make clear the trace element fractionation (U and Pb) on a sample surface during LA-ICPMS measurements and establish the high precision measurements of Pb isotope ratios based on the authentic carbonate standard materials. Therefore, we made efforts to find natural carbonates as possible standard materials with homogeneous U and Pb contents as well as Pb isotope ratios. Imaging analyses (two-dimensional mapping) of the trace element contents and the isotope ratios were adopted to decide the suitable sample analysis points by laser ablation for the radiometric dating of carbonates 1). Besides, we performed high precise and sensitive measurements in Pb isotope ratios by the LA-ICPMS using the multiple ion counters and the multiple Faraday collectors with high gain amplifiers 1).
(2) Redox potential by the theoretical calculation
For the inorganic geochemical analyses, drilling core samples (DH5, 6, 7, 8, 12) from southeastern Gifu in the middle Japan, and modern carbonate deposits from Shimane and Yamanashi in Japan were analyzed by ICP-MS. For the DH6, 7, 8, calculated redox potential values by the Fe contents were coincident with the observed values of ground water. However, those of other samples showed disagreement with the observed values, which could be caused by secondary mixing with oxic surface water. Therefore, applicable methods and condition (e.g. range of the redox potential values, ground water source and/or their matrices) should be cleared for the theoretical calculation of redox potential by Fe contents in carbonates.
This study was carried out under a contract with METI (Ministry of Economy, Trade and Industry) as part of its R&D supporting program for developing geological disposal technology.
1) JAEA, 2014 Annual report on METI (Ministry of Economy, Trade and Industry) R&D supporting program for developing geological disposal technology, 2015, 229p. in Japanese
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3) Arthur et al., Geochem. Explor. Environ. Anal., vol.6, 2006, pp.33-48.
4) Mizuno and Iwatsuki, Chikyukagaku (Geochemistry), vol. 40, 2006, pp.33-45. in Japanese with English abstract
5) Becker et al., Earth Planet. Sci. Lett., vol.203, 2002, pp.681-689.