Anatomy Of A Middle Miocene Valles-Type Caldera Cluster- Geology Of The Okueyama Volcano-Plutonic Complex, Southwest Japan

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Journal Article: Anatomy Of A Middle Miocene Valles-Type Caldera Cluster- Geology Of The Okueyama Volcano-Plutonic Complex, Southwest Japan

Abstract
A deeply eroded root of a Miocene Valles-type caldera cluster is exposed in the Okueyama volcano-plutonic complex in Kyushu, southwest Japan. The complex shows the relationship between an ash-flow caldera and a vertically zoned granitic batholith. The igneous activity of this complex began with the eruption of the Sobosan dacitic tuff and collapse of the Sobosan cauldron (18 _ 13 km). After an erosion interval, the Katamukiyama aphyric rhyolitic lavas were erupted to form a thick lava plateau, followed by the eruption of Katamukiyama dacitic tuffs concurrent with the formation of the Katamukiyama cauldron (12 _ 6 km). Some dikes of felsite and tuff breccia and a stock of hypersthene-biotite granodiorite are closely related to this stage of volcanism. After an erosional interval, eruption of the Sobosan andesitic and dacitic lavas and pyroclastics constructed three large stratovolcanoes, and their eruptive centers migrated from SW to NE. Stocks of pyroxene-bearing quartz monzodiorite to porphyritic granophyre intruded the centers of the stratovolcanoes, and are probably vent-filling intrusives. After an erosional interval, the Kunimidake rhyolitic tuff erupted to form the Okueyama cauldron (33 _ 23 km). The Sobosan and Katamukiyama cauldrons subsided again during this stage; large ring-shaped dikes of granite porphyry were formed as vent-filling intrusives of this volcanism. The Okueyama granitic batholith, the product of the final magmatic activity in this complex, is a solidified resurgent magma chamber displaying vertical zonation, which intruded to 3 km beneath the surface. In this zoned pluton, upper biotite granite (74-70 wt. % SiO2) gradually changes to lower hornblende-biotite granodiorite (66-65 wt. % SiO2). The age of the batholithic pluton given by K-Ar dating is about 14 Ma, and the igneous activity of the Okueyama complex would have lasted for a relatively short time span during the middle Miocene.

Author 
Masaki Takahashi








Published Journal 
Journal of Volcanology and Geothermal Research, 1986





DOI 
Not Provided
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Citation

Masaki Takahashi. 1986. Anatomy Of A Middle Miocene Valles-Type Caldera Cluster- Geology Of The Okueyama Volcano-Plutonic Complex, Southwest Japan. Journal of Volcanology and Geothermal Research. (!) .