Geosphere stability project, 6; Chronological and chemical analyses of carbonate minerals

Watanabe, Takahiro   ; Kokubu, Yoko   ; Murakami, Hiroaki  ; Yokoyama, Tatsunori   ; Amamiya, Hiroki; Mizuno, Takashi   ; Kubota, Mitsuru; Iwatsuki, Teruki  

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.