東北日本の第四紀火山活動におけるマグマ中のH_2O量の水平変化

概要

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Quaternary volcanoes in northeastern Japan are grouped into three categories; (1) volcanoes without lavas or pyroclastic rocks containing hornblende and biotite phenocrysts, (2) volcanoes with lavas or pyroclastic rocks containing hornblende phenocrysts and without rocks containing biotite phenocrysts, (3) those with lavas and pyroclastic rocks containing biotite phenocrysts. Volcanoes with rocks containing biotite phenocrysts are located in the region far from the volcanic front whereas those without any hydrous mineral phenocrysts distributed on the volcanic front. Volcanoes in a belt between above two belts empted rocks containing only hornblende as hydrous mineral phenocrysts. Experimental works on calc-alkalic andesite-dacite compositions under H_20-saturated and undersaturated conditions (Piwinskii and Wyllie; 1968, Robertson and Wyllie; 1971, Eggler; 1972, Eggler and Burnham; 1973) suggest that (1) liquidus temperature of hornblende is higher than that of biotite under intracrustal pressure condition (<10kb), (2) liquidus temperatures of hornblende and biotite are not appreciably affected by the change of H_20 contents and bulk chemical composition of the magma. Therefore, lateral change of phenocryst assemblage suggests that the temperature of original magma increases toward volcanic front.
特定非営利活動法人日本火山学会の論文
1977-12-15