強磁性鉱物の主成分によるテフラの同定の基礎的研究

概要

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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_2O_3 and TiO_2 content. The present procedure was unsuccessful in further purification of the ferromagnetic fraction. The TiO_2 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_2 content of 10 to 12%. Even such tephras can be identified by comparing their TiO_2 content with that of adjacent tephras layers, due to a characteristic TiO_2 distribution pattern found in the studied tephras (See Fig. 8).
日本地球化学会の論文
1983-12-25