- 著者
- Isoji Miyagi Osamu Matsubaya Satoru Nakashima
- 出版者
- GEOCHEMICAL SOCIETY OF JAPAN
- 雑誌
- GEOCHEMICAL JOURNAL (ISSN:00167002)
- 巻号頁・発行日
- vol.32, no.1, pp.33-48, 1998-02-20 (Released:2008-04-08)
- 参考文献数
- 55
- 被引用文献数
- 17 25
The hydrogen isotopic composition of hornblende in volcanic rocks has potential to indicate processes such as degassing of a magma reservoir, as well as the origin of magmatic water. However, during eruption and high-temperature interaction with air, the isotope composition of hornblende can be altered. In order to establish criteria to select natural hornblende that preserves magmatic hydrogen isotopic ratios, hydrogen isotopic composition (δD), water contents, and colors of hornblendes were measured. A series of heating experiments on natural green hornblendes was conducted in air and under vacuum up to 1000°C. There observed a negative relationship between the intensity of redness (a∗) and water content among heated hornblendes in air and under vacuum, as well as natural samples from several Quaternary volcanos in Japan. Heating hornblende results in a significant increase in δD value that can be explained by a Rayleigh distillation (simultaneous degassing without hydrogen isotopic exchange between the gas and the mineral) model involving degassing of both H2O and H2. According to the model, maximum fractionation occurs when hornblende dehydrates only by H2 degassing. Application of the model indicates that hornblendes in pumice fragments from Plinian eruptions are most representative of the δD of pre-eruptive magma. In contrast, the δD values of minerals from lava flows, lava domes, or even from thick pumice flow deposits may have suffered from 1) hydrogen isotopic fractionation by mineral dehydration, and/or 2) isotopic re-equilibration with degassing magma during eruption stage and during cooling stage after the emplacement.
- 著者
- AYA SAKAGUCHI AKINOBU KADOKURA PETER STEIER KAZUYA TANAKA YOSHIO TAKAHASHI HARUKA CHIGA AKIHITO MATSUSHIMA SATORU NAKASHIMA YUICHI ONDA
- 出版者
- GEOCHEMICAL SOCIETY OF JAPAN
- 雑誌
- GEOCHEMICAL JOURNAL (ISSN:00167002)
- 巻号頁・発行日
- vol.46, no.4, pp.355-360, 2012-08-20 (Released:2013-11-08)
- 参考文献数
- 26
- 被引用文献数
- 90 27
Concentrations of the radionuclides, U, Pu, and Cs were measured in water samples (10-20 L) to study analyte dispersion and migration following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. A total of 8 water samples including oceanic water and paddy-field water were collected in the vicinity of the plant. Determinations of U, Pu and Cs isotopes were performed by accelerator mass spectrometry (AMS), inductively coupled plasma mass spectrometry (ICP-MS), and γ-ray spectrometry. The 236U/238U atom ratio was in the range 1.83-8.20 × 10-9 for fresh water and around 0.57 × 10-9 for seawater while the concentration of 236U was about 104-105 and 106 atoms/kg, respectively. Plutonium (239,240Pu) was detected in one riverine sample and the marine samples at very low levels and with large uncertainty. The concentrations of 137Cs in fresh riverine samples were 0.02-0.46 Bq/kg which are more than three orders of magnitude larger than the global fallout level. As for seawater samples within 80 km offshore of the FDNPP, the concentrations of 137Cs were 10-20 times higher than that of the Japan Sea water. Also 134Cs and 137Cs were of similar concentrations in all samples. The results show that volatile and refractory nuclides such as Cs, U and Pu exist in the dissolved phase, which can be readily assimilated by plants/humans. However the environmental impact of Pu and U in the vicinity of the FDNPP is considered to be low in comparison to that of the volatile radionuclide Cs.