Identification of Lower Pleistocene widespread tephras associated with large caldera-forming eruptions in the Tohoku area,north-east Japan |
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| Authors: | Takehiko Suzuki Seiji Maruyama Tohru Danhara Takafumi Hirata Hiroshi Machida Fusao Arai |
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| Institution: | 1. Department of Geography, Tokyo Metropolitan University, 1-1 Minamiosawa, Hachioji, Tokyo, 192-0397 Japan;2. Kyoto Fission-Track, Co., Ltd, 44-4 Oomiyaminamitajiri-cho, Kita-ku, Kyoto, 603-8832 Japan;3. Geochemical Research Center, Graduate School of Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan;4. Faculty of Education, Gunma University, 4-2 Aramaki-machi, Maebashi, Gunma, 371-8510 Japan
Deceased 11 February 2004 |
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| Abstract: | Tephra fingerprinting techniques contributing to volcanology and palaeoenvironmental studies have been developed using a combination of laser-ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). In particular, femtosecond LA-ICP-MS can determine major- and trace element abundances in individual glass shards. On the basis of the major oxide and trace element composition of the glass shards, using those methods, we re-examined the identification of four lower Pleistocene tephras originating from north-east Japan. All trace element abundances exhibited the typical pattern of tephras from the Hokkaido–Tohoku area, and major element concentrations were distinct. As a result, we re-examined the correlation of the widespread Tmg-R4 tephra (2.0 Ma), and newly defined the widespread Kd44-Naka tephra (1.968–1.781 Ma), both originating from the Sengan geothermal region. Furthermore, we re-examined identifications of Sr-Asn-Kd8 (1.219 Ma) and Sr-Kc-U8 (0.922–0.910 Ma) in central Japan, both derived from the Aizu volcanic region. The extensive distributions of the former two tephras suggest the occurrence of two large caldera-forming eruptions (Volcanic Explosivity Index 7) during a short period. Also, the distributions and volumes of the latter two tephras are broader and larger than those previously assumed. The results provide insight into large volcanic eruption history and terrestrial and marine palaeoenvironmental history. |
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| Keywords: | femtosecond LA–ICP–MS lower Pleistocene north-east Japan SEM-EDS widespread tephra |
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