Change in catastrophic eruptions the volcanic processes from the continental margin to the island arc

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The igneous activity along the Eurasian continental margin in Cretaceous to Paleogene is characterized by catastrophic eruptions associated with cauldron formations. This study focuses on the dating of the cauldrons in the central Chugoku district, where insufficient data are only known.(1) Futakamiyama cauldron. Andesitic agglutinate of the cauldron infill: 83±13Ma (Rb-Sr isochlon); granodiorite porphyry: 72.8±1.8 Ma (hornblende K-Ar); quartz diorite: 66.6±2.4 Ma (hornblende K-Ar); hornblende-biotite granite (the basement rock): 85.2±1.9Ma (hornblende K-Ar). These ages suggest that the volcanic activity of the Futakamiyama cauldron occurred during 85 - 73Ma.(2) Hikihara cauldron. Rhyolitic welded tuff of the cauldron infill: 73.2±2.5Ma (FT); quartz porphyry: 69.0±2.2Ma (FT); biotite granite: 63.1±2.3Ma (Rb-Sr isochlon). These ages suggest that the volcanic activity of the Hikihara cauldron occurred during 75 - 60Ma.(3) Sakuto cauldron. Rhyolite lava of the cauldron infill: 77.3±4.3Ma (Rb-Sr isochlon); quartz diorite: 71.3±3.7Ma (hornblend K-Ar). These ages suggest that the volcanic activity of the Sakuto cauldron occurred during 80 - 70Ma.(4) Yanahara cauldron. Quartz diorite: 79.8±1.8Ma (hornblend K-Ar). This suggests that the volcanic activity of a cauldron occurred in ca. 80Ma.Accordingly, these data show that the catastrophic eruptions associated with cauldrons concentrated in the central Chugoku district during 80 - 70Ma. This hotspot-like volcanism was replaced by the Paleogene (44 - 30Ma) arc volcanism with a clear volcanic front.