Identification of provenance rocks based on EPMA analyses of heavy minerals

重鉱物のEPMA分析に基づく後背地岩体の同定

清水 麻由子   ; 佐野 直美; 植木 忠正; 代永 佑輔; 安江 健一*; 丹羽 正和   

Shimizu, Mayuko; Sano, Naomi; Ueki, Tadamasa; Yonaga, Yusuke; Yasue, Kenichi*; Niwa, Masakazu

Information about mountain formation is significant in the field of geological disposal of high-level radioactive waste, because this affects long-term fluctuation in groundwater flow system. Provenance analysis is one of effective approaches for understanding formation process of mountains. Chemical compositions of heavy minerals, as well as their chronological data, can be an index for identification of provenance rocks. The accurate identification requires the measurement of as many grains as possible. In order to achieve an efficient provenance analysis, we developed a method for quick identification of heavy minerals using an Electron Probe Micro Analyzer (EPMA). This method was applied to the sediments where provenance rocks had lithological variations but similar formation ages. Consequently, the provenance rocks were identified based on chemical compositions of heavy minerals resistant to weathering, such as zircon and ilmenite.