強磁性鉱物の主成分によるテフラの同定の基礎的研究 [in Japanese] A fundamental study of identification of marker-tephras by means of main chemical composition of ferromagnetic minerals [in Japanese]
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This paper deals with the identification of tephras by chemical analysis of ferromagnetic fraction contained in them. The samples used for this study were taken from the Late and Middle Pleistocene tephras at the Oiso Hill, 25 km to the east of Hakone Volcano. Ferromagnetic fraction, separated from each sample, was powdered and pro- cessed by hydraulic elutriation until any transparent minerals were not found by microscopic examination. The purity of the obtained fraction was estimated to be 93 to 95% in terms of FeO, Fe<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> content. The present procedure was unsuccessful in further purification of the ferromagnetic fraction. The TiO<sub>2</sub> content of the fraction gives a clue for identifying the tephras, except for two-pyroxene andesitic tephras, originated from Hakone Volcano, which have a uniform TiO<sub>2</sub> content of 10 to 12%. Even such tephras can be identified by comparing their TiO<sub>2</sub> content with that of adjacent tephras layers, due to a characteristic TiO<sub>2</sub> distribution pattern found in the studied tephras (See Fig. 8).
Chikyukagaku 17(2), 109-117, 1983
The Geochemical Society of Japan