Zoning type of a plagioclase in the volcanic rocks from the Myoko and Yakeyama volcanoes, Niigata Prefecture, Japan

概要

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The volcanic rocks of the Myoko and Yakeyama in Quaternary are distributed in the Nishikubiki region, Niigata Prefecture. In the Myoko volcano, pyroxene and hornblende andesites are common, and basalt is accompanied in subordinate amount. The volcanic rocks from the Yakeyama are pyroxene - hornblende andesite and hornblende dacite. The zoning types of plagioclase from these volcanic rocks are diverse. It is possible to be classified six types such as fresh, small dusty and big dusty zones at marginal or core parts, sieve-like and fingerprint-like textures. The major zoning type of plagioclase in andesite and dacite from the Yakeyama and Myoko volcanoes at the late stages are fresh type with normal zoning. The chemical variations of major and trace elements of the fresh plagioclase bearing volcanic rocks are plotted far distance from the differentiation trend. The plots of andesites with the various zoning types of plagioclase from the Myoko volcano are a wide dispersion in FeO/MgO-Si0_2 diagram.
上越教育大学の論文
2000-09-00