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Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*
JAEA-Testing 2021-001, 49 Pages, 2021/08
JAEA-Testing-2021-001.pdf:3.86MB
To make a contribution to safety assessment for geological disposal of high level radioactive and/or TRU waste, we need to assess long-term stability of geological environment and predict long-term changes of geotectonic events that will occur in the future, especially for Quaternary period (
2.6 million years ago-present). In the most case, we investigate chronological data of geological events by radiometric dating. When some geological samples have no objects to which radiometric dating method can be applied (e.g., zircon, biotite, wood fragments and plant residues), we can use tephrochronology, which is geological dating method using each layer of tephra (erupted volcanic ash), for dating of geological layers. This chronological method is essential in Japan, where volcanism is very active. Tephra is usually characterized by petrographic characteristics and/or chemical composition (mainly major elements) of volcanic glasses and/or minerals in tephra. In Tono Geoscience Center (Japan Atomic Energy Agency), we develop an analytical technique of chemical composition including trace elements of volcanic glasses for detailed tephra identification. In this paper, we report a sample preparation procedure and analytical methods of chemical compositions of individual volcanic glass shards by using an electron probe microanalyzer and a laser ablation-inductively coupled plasma-mass spectrometer.
Futakuchi, Katsuhito*; Sakuramoto, Yuji*; *; *; *; Hashimoto, Shuji*
PNC TJ1308 98-001, 103 Pages, 1998/02
None
Futakuchi, Katsuhito*; Sakuramoto, Yuji*; *; *; *
PNC TJ1308 97-001, 295 Pages, 1997/02
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PNC TJ1308 93-002, 35 Pages, 1993/02
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PNC TJ1308 93-001, 91 Pages, 1993/02
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Futakuchi, Katsuhito*; Sakuramoto, Yuji*
PNC TJ1308 92-001, 107 Pages, 1992/02
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Kagami, Saya; Niwa, Masakazu; Umeda, Koji*; Danhara, Toru*; Fujita, Natsuko; Nakanishi, Toshimichi*; Kamataki, Takanobu*; Kurosawa, Hideki*
no journal, ,
The Kikai-Akahoya (K-Ah) volcanic ash from the 7.3 Ka Kikai caldera eruption is one of the representative tephra of the Quaternary. We newly found the event deposit associated with the tsunami of the K-Ah eruption in the core (MMS1) from the Miyazaki Plain. Here, we present the results of tephra analysis and 
C dating of samples in the MMS1 core. The sediments between 10.4 m and 12.0 m in depth contained volcanic glasses and pumices that developed planar lamination with sand, indicating that tephra was deposited secondarily as submerged sediments. A previous study founded the similar sediments in a river near the boring site and interpreted to be deposit of tsunami during the 7.3 Ka Kikai caldera eruption. The results of C ages and identification by chemical composition and refractive index of volcanic glass are consistent with the assumption that the sediments between 10.4 m and 12.0 m in depth were tsunami sediments related to the K-Ah eruption. Chemical composition of volcanic glass in the K-Ah tephra is bimodal: 65wt.% (Type L) and 75wt.% (Type H) of SiO
concentration. Previous studies suggested that Type H erupted in the early K-Ky eruption, and then the magma mixed with Type L erupted in the late K-Ky eruption. The samples contained the K-Ah volcanic ash in this study consist of mainly Type H and slightly Type L. Type H from 11.810.2 m depth was subdivided into two clusters and that from 12.3 m depth contained only one cluster of higher SiO concentration. The feature of the volcanic glasses may indicate the change in magma composition during the eruption.
Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*; Yasue, Kenichi*; Niwa, Masakazu; Furusawa, Akira*; Tamura, Itoko*
no journal, ,
Tephrochronology is important to understand geotectonic events for the last few Myr. Tephra is usually characterized by petrographic characteristics and chemical compositions (mainly major elements) of volcanic glass shards. When tephras similar in the characteristics are discriminated, trace element compositions are valid for identification of tephra. We focus on the enrichment of the database of trace elements compositions in widespread tephras, which is not reported enough. We used EPMA and LA-ICP-MS for major and trace element concentration of volcanic glass shards in Znp-Ohta tephra and Tng tephra, of which major elements similar to Znp-Ohta tephra. In this study, it was clear that Znp-Ohta tephra had zirconium concentration [Zr] = 44-58 ppm and Zr/Pb = 2.5-3.4, while Tng tephra had [Zr] = 70-81 ppm and Zr/Pb = 3.8-4.6. Znp-Ohta and Tng tephras were discriminated not only by characteristic type, Ba/La, and La/Y of glass shards (Tamura and Yamazaki, 2004) but also by Zr-Pb correlation. In the future, we compare the trace element concentrations of Znp-Ohta tephra in multiple sites for evaluation of secondary effect during the deposition.