瀬戸内火山岩類の火山活動時期および分布範囲について : 瀬戸内火山岩類の年代測定, その5

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Four Neogene volcanic rocks in the Kyushu district, which have been estimated to belong the Setouchi volcanie rocks, yielded different K-Ar ages, i.e., 13.2 Ma (southern part of Oita Pref.), 8.3 Ma (Saga Pref.), <4.3 Ma (Uku-Jima) and 3.2 Ma (northern part of Oita Pref.). Only a glassy rock from Mt. Daisango-Yama, southern part of Oita Pref. has a K-Ar age (13 .2 Ma) equivalent to those of the Setouchi volcanic rocks in other districts, i.e., 12±1 Ma. On the basis of different K-Ar ages and petrochemical chracteristics from the Setouchi volcanic rocks, the Sanukite-like volcanic rocks in Kyushu, except for that from the southern part of Oita Pref., are not to be classified as the Setouchi volcanic rocks. It is concluded on the basis of the present and previous results that volcanic activity in the Setouchi volcanic zone occurred 12±1 million years ago and extends as long as 1000 km from the eastern part of the Kyushu area (Mt. Daisango-Yama area) to the Choshi area, as a result of the Miocene plate subduction.
1980-10-01