Abstract
Our previous K-Ar chronology and volcanostratigraphic investigations of the Minami Zao volcano revealed that it started its volcanic activity about 1.2 Ma in the northwesten part of the region (Mt. Sugigamine and Mt. Maeyama area), and major activity started 0.6 Ma. There exist, however, several disagreements between the K-Ar ages and volcanostratigraphic sequences. Newly obtained K-Ar ages suggest that the 1.2 Ma activity also occurred in the southern part of the volcano. Reverse magnetization of the sample is consistent with the 1.2 Ma age. We name this "the old-Fubo" activity. The activities between 1 to 1.2 Ma are also found in the North Zao (Mt. Ryuzan) and Central Zao (Roba no Mini iwa=Donky ear rock). The second period of the activity started around 0.5 Ma. From the volcanostratigraphy view, subsequently occurred the third period of the activity, but no gap was found between these activities from the K-Ar study. The most active period was around 0.3 Ma. Disordance between K-Ar ages and volcanostratigraphic have been lessen but still exists.
