- 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.
- 著者
- HIKARU IWAMORI HITOMI NAKAMURA
- 出版者
- GEOCHEMICAL SOCIETY OF JAPAN
- 雑誌
- GEOCHEMICAL JOURNAL (ISSN:00167002)
- 巻号頁・発行日
- vol.46, no.4, pp.e39-e46, 2012-08-20 (Released:2013-11-08)
- 参考文献数
- 37
- 被引用文献数
- 6 22
In order to decipher the mantle geochemical heterogeneity that reflects material differentiation and circulation within the Earth, we examined mid-ocean ridge basalts (MORB), ocean island basalts (OIB) and arc basalts (AB), in terms of the radiogenic isotopic variability and its geographical distribution. It has been found that the Sr, Nd and Pb isotopic ratios of MORB, OIB and AB exhibit a two-dimensional structure, and are mostly distributed on the same compositional plane that is spanned by two independent components (IC1 and IC2). One of the two components (IC2) divides geochemically the mantle broadly into the Eastern and Western Hemispheres. Inspection of the geochemical nature of IC2 suggests that it may represent a fluid mobile component recycled through subduction zones. The mantle geochemical domain beneath the Eastern Hemisphere is enriched in the fluid mobile component, possibly by focused subduction towards the supercontinent Pangea which was surrounded by subduction zones. Although the present-day continents have been dispersed since then, the geochemical domain has seemingly been anchored to the asthenosphere without moving with the continents.