5 0 0 0 OA 何を分析に加えるべきか : 浜中評・小林評へのリプライ
- 著者
- Rofiqul Umam Masaharu Tanimizu Hitomi Nakamura Yoshiro Nishio Ryo Nakai Naoto Sugimoto Yasunori Mori Yuuki Kobayashi Akane Ito Shigeyuki Wakaki Kazuya Nagaishi Tsuyoshi Ishikawa
- 出版者
- GEOCHEMICAL SOCIETY OF JAPAN
- 雑誌
- GEOCHEMICAL JOURNAL (ISSN:00167002)
- 巻号頁・発行日
- vol.56, no.5, pp.e8-e17, 2022 (Released:2022-10-18)
- 参考文献数
- 28
- 被引用文献数
- 3
Slab-dehydrated fluid is considered to be involved in island arc magmatism. In this study, Li isotope ratios were determined for deep groundwater samples from the non-volcanic forearc region of SW Japan. The contribution of the slab-dehydrated fluid from the Philippine Sea Plate (PHS) was investigated in the Arima area and the eastern Kii Peninsula area, corresponding to the slab depths of ~60 km and 20–30 km, respectively. In the Arima area, the high-temperature thermal waters with high salinity called the Arima-type fluid were clarified to have low δ7Li values of +1–+3‰. The low δ7Li values with high Li concentrations are thought to be the result of fluid-rock interactions at high temperatures, which is consistent with the characteristics of the slab-dehydrated fluid. On the other hand, the δ7Li values of deep groundwaters in the eastern Kii Peninsula showed a wide range of +2 to +29‰. Several groundwater samples had a similar chemical property to the Arima-type fluid: low δ7Li values, low Cl/Li ratios, and 87Sr/86Sr ratios around 0.708–0.710. They are distributed along the Median Tectonic Line (MTL) and within about 20 km south of the MTL. These results indicate a common supply of slab-dehydrated fluids to the non-volcanic forearc region in SW Japan from PHS along the large faults, and Li isotope ratios will be a useful indicator to detect their contribution.