地球化学

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For the purpose of contributing to tephrochronology and clarifying the mechanism of their volcanic effusion, the relationship between chemical composition of titanomagnetite and coexisting colored minerals (olivine, pyroxene, hornblende, and biotite) in the volcanic ashes and fall pumices was studied for selected samples from many horizons widely distributed in Kanto and Shinshu districts in central Japan. In the case of fall pumices, the TiO₂ content of titanomagnetite gradually decreases from basic fall pumice (olivine-bearing) to acidic one (hornblende-bearing), and it seems to be pos- sible to deduce the properties of rocks at the time of eruption on the basis of the TiO₂ content of titanomagnetite even in the horizons which were significantly weathered and lost colored minerals. On the other hand, the TiO₂ content of titanomagnetite in volcanic ashes has little reference to the colored minerals, and it seems to be difficult to estimate the properties of fresh ashes just after eruption.

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