強磁性鉱物中の微量成分によるテフラの同定法

概要

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To establish a method for the identification of tephras by chemical means, some minor components (V_2O_3, MnO, ZnO) in ferromagnetic minerals were determined together with their major components (FeO, Fe_2O_3, TiO_2). The effects of the contamination of micro-components from the ferromagnesian silicate minerals co-existing with ferromagnetic mineral specimens were carefully examined. The MnO contents of pyroxenes or hornblendes are slightly higher than that of ferromagnetic minerals, th influence, however, can be neglected if the purity of the sample (presented as FeO+Fe_2O_3+TiO_2%) is higher than 93%. More than 200 samples of 100 layers of marker-tephras taken from South-Kanto, North-Kanto, Shinshu and Aomori Loams were studied. Among the ratios of the chemical components in the ferromagnetic minerals, Mn/Fe, V/Ti, V/Mn, and Zn/V values widely and thus seem to be effective for the identification of these tephras. Closer examination of the chemical data indicates that the following combination of elements is very useful for identification of almost all tephras; the tephras are first classified in terms of TiO_2 content of ferromagnetice minerals, then subdivided on the basis of the Mn/Fe vs. V/Ti (or V/Mn vs. Zn/V) correlation diagrams for each TiO_2-group.
地学団体研究会の論文
1986-05-25