Abstract
We determined K-Ar ages and whole-rock chemistry for volcanic rocks from Azumaya volcano and the surrounding area of central Japan, in order to reexamine its volcanic history. Based on our chronological and petrological study, coupled with previous geological data, we reconstructed the volcanic history of the volcano. The volcano consists of three volcanic edifices (the Initial volcanic edifice, the Nekodake volcanic edifice, and the Urakurayama volcanic edifice). Volcanic activity started at ~0.8 Ma, forming the Initial volcanic edifice, which consists mainly of dacitic and basaltic andesitic lavas. At ~0.7 Ma, dacitic volcanic activity started around Nekodake and formed the Nekodake volcanic edifice within several tens of thousands of years. Activity of the Initial volcanic edifice ceased at ~0.55 Ma. After a dormant period of approximately 50,000 years, andesitic lavas effused from the eastern slope of the Initial volcanic edifice at ~0.5 Ma, forming the Urakurayama volcanic edifice and ceasing at ~0.45 Ma. Subsequently, a small volcano (Naruiwa volcano) erupted in the northwestern region of the Azumaya volcano at ~0.3 Ma.
