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Kojima, Satoru*; Kagami, Saya; Yokoyama, Tatsunori; Kariya, Yoshihiko*; Katayama, Yoshikazu*; Nishio, Gaku*
Proceedings of 5th International Workshop on Rock Mechanics and Engineering Geology in Volcanic Fields (RMEGV 2021) (Internet), 6 Pages, 2021/09
A local tephra embedded in a hand-auger boring core drilled at near-shore of Kinugasanoike Pond about 4.6 km NE of Mt.Yakedake, one of the most active volcanoes in central Japan, is composed mainly of several kinds of volcanic glass shards (microlite-bearing, blocky, fluted and micro-vesicular types) with minor amounts of crystal minerals including quartz, plagioclase, hornblende, biotite, and pyroxene. Plant remains recovered from the horizon 10 cm below the tephra layer yield 
C ages of 2,331-2,295 (19.2% probability distribution) and 2,270-2,155 (76.2% probability distribution) cal yrs BP. We measured major element compositions of 241 individual glass shards using Electron Probe Micro Analyzer. They are plotted on the SiO
-KO, SiO-NaO+KO, and FeO
-KO diagrams in a region different from those of major regional tephras distributed in central Japan. The clast and chemical compositions coincide with those of a tephra embedded in the Nakao pyroclastic flow deposits distributed about 2 km NNW of Mt. Yakedake dated as around 2,300 cal yrs BP. The tephra could be used as a local marker of 2,300 cal yrs BP in the southern part of Northern Japan Alps.
Ueki, Tadamasa; Niwa, Masakazu; Iwano, Hideki*; Danhara, Toru*; Hirata, Takafumi*
Chishitsugaku Zasshi, 125(3), p.227 - 236, 2019/03
no abstracts in English
Kagami, Saya
no journal, ,
Tephrochronology, which uses tephra to determine the chronostratigraphy of strata is important to understand geotectonic events for the last few Myr. 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 are similar to that of Znp-Ohta. These two tephras could be distinguished by rare earth elements pattern, in addition to the conventional indices. Identification of tephras by more than one indicator could distinguish tephra with similar characteristics and prevent incorrect stratigraphic correlation. It is necessary to improve the chemical composition database of wide-spread tephras including trace element compositions, and we plan to measure various wide-spread tephras by the method in this study.
