Mechanism of formation of Cretaceous to Paleogene cauldron in Chugoku district, Japan

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Cretaceous to Paleogene volcanic rocks and granitic batholiths are extensively distributed in the Inner zone of Southwest Japan. This project includes structural geology, petrology, geochemistry on the Cretaceous to Paleogene cauldrons in the Chugoku district, Southwest Japan. The scale model experiments were also carried out in order to simulate the formation process of the cauldron.From these studies, we found new caulderons, i.e., Niimi caldron and Yamaguchi cauldron in the Niimi area, Okayama Prefecture and Yamaguchi city ; respectively. These cauldrons show volcano-plutonic complexes. From the scale model experiments under centrifuge acceleration, it is inferred that the fracturing of the polygonal cauldron is influenced by the pre-existed basement structures such as faults.