伊豆・天城火山群の岩石学的および化学的性質

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Amagi Volcanoes, which are situated in the eastern part of the Central Izu Peninsula, comprise a main shield volcano of lava flows, cinder or scoria cones and more than twenty parasitic vents from which pyroclastic rocks were erupted. The volcanic activities are summerized as follows: olivine basalt to olivine-bearing hornblende-hypersthene-augite- dacite from three parasitic vents ・・・・・ Recent basaltic rocks (most of them are contaminated by granitic rocks)・・late Pleistocene〜Recent a large scale eruption of hornblende-bearing two-pyroxene andesite of hypersthenic rock series ・・・・・ Pleistocene. The basaltic lavas are high in MgO : FeO + Fe_2O_3 ratio, in Al_2O_3 and in alkalies, especially in Na_2O. Some of them have a considerable amount of olivine, while their normative feldspar is not so high in An. Sometimes, they contain resorbed xenocrysts derived from granitic rocks. The alkali-lime index ranges from 65 to 66. These figures indicate the basaltic lavas of Amagi volcanoes are richer in alkalies than in those of the Izu-Hakone regions. The above mentioned characters are strikingly similer to those of the northern subzone of the Huji Volcanic Zone and of the Nasu Zone. Moreover, the basaltic lavas have a intermediate character, especially in richness of Al_2O_3, between the extremely tholeiitic rock suite of the southern subzone of the Huii Volcanic Zone and the alkalic rock suite of the Circum-Japan Sea Province. In this paper, the writer described the geologic, petrographic and chemical characters of these lavas. Petrogenetic problems will be discussed in near future.
地学団体研究会の論文
1959-10-30

伊豆・天城火山群の岩石学的および化学的性質

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