岩鉱
Online ISSN : 1881-3275
Print ISSN : 0914-9783
ISSN-L : 0914-9783
論説
八幡平火山群の地質とマグマ組成の時間—空間変化
大場 司梅田 浩司
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ジャーナル フリー

1999 年 94 巻 6 号 p. 187-202

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Northern part of Hachimantai volcanic field, northeastern Japan, comprises four stratovolcanoes, Hachimantai, Chausudake, Nishimoriyama, and Maemoriyama volcanoes, and many flank volcanoes, Appidake, Fukenoyu, Gentamori, Ebisu-Daikoku-mori, and an eroded volcano. K-Ar dating and geological survey revealed that Hachimantai and Chausudake volcanoes erupted about during 0.7-1 Ma, Ebisu-Daikoku-mori volcano erupted about 0.4 Ma, and ages of the products of Maemoriyama volcano are younger than 0.4 Ma. Although compositional range of the rocks from whole of the field is wide, chemical variation of rocks from individual volcano is relatively small. There is little correlation of chemical compositions with age, oppose to distinct spatial variation in the volcanic field, that basaltic lavas distribute in the eastern and northern part, and andesite lavas in the southern and western part. Spatial 87Sr/86Sr variation, that decreases from east to west, is corresponded with the trend of whole of the arc. The magmas were derived from lithosphere which heterogeneity was resulted in the spatial 87Sr/86Sr variation.

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© 1999 日本鉱物科学会
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