能登半島北部の新第三紀火山岩類 : 特に無斑晶質安山岩類について
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概要
- 論文の詳細を見る
Aphyric andesites, which are characterized by lack of plagioclase phenocryst, are mainly divided into two groups; olivine andesite and clinopyroxene-bronzite andesite. These rocks are formed in consequence of fractional crystallization of calc-alkallne andesite magma. The order of crystallization of sli1cate minerals is olivine→orthopyroxene→clinopyroxene→plagioclase. As temperature decreased, olivine changes to bronzite by reaction between olivine crystal and residual liquid. The chemical composition of bronizite grades into hypersthene and inverted to pigeonite. Compositional change of clinopyroxene is from sallite to angite, but slightly scatters in pyroxene diagram. The volcanic activity of aphyric andesites, which takes place mainly on land environment, is regarded as calc-alkaline andesite activity prior to transgression during Green Tuff movement. These rocks are associated with large volumes of pumice flow and small volumes of tholeiitic olivine basalt and alkali olivine dolerite. Namely, Neogene volcanic rocks in this region belong to three rock series. As Funazu granitic and Hida metamorphic basement in the Noto Peninsula being stable during Tertiary time, it might be stated that the volcanism of aphyric andesites took place on comparatively thick crust in island arcs.
- 日本地質学会の論文
- 1984-11-30