Abstract
We determined the K–Ar ages of 21 samples from the Asama–Eboshi volcanoes in central Japan in order to understand the long-term spatial migration of Quaternary eruptive centers in this region. These volcanoes consist of a series of WNW–ESE aligned stratovolcanoes and surrounding monogenetic volcanoes. Our new K–Ar dates and previously reported ages show that volcanic activity can be classified into four stages separated by dormant periods as follows. (1) During Stage I (ca. 1.0 Ma) and Stage II (0.85–0.75 Ma), magma was erupted from the western part of these volcanoes and produced the Eboshidake stratovolcano followed by monogenetic volcanoes on the western side of this volcano. (2) In Stage III, volcanic reactivation of Eboshidake took place at ca. 0.45 Ma and formed the Kakuma–Nabebutayama stratovolcano at ca. 0.35 Ma. Volcanic activity in the western area ceased at ca. 0.3 Ma, and then Stage III volcanism extended towards the ESE resulting in the formation of Sanpogamine and Takamineyama stratovolcanoes (ca. >0.24 Ma). (3) In Stage IV, lava domes (e.g., Hanareyama; 0.02 Ma) and stratovolcanoes (e.g., Kurofuyama; ca. 0.10 Ma) were produced in the central and eastern areas. The currently active Maekakeyama stratovolcano began erupting at ca. 8.5 ka. Monogenetic volcanism was limited to brief periods at ca. 0.8, 0.3, 0.1, and 0.02 Ma. Volcanic activity associated with the Asama–Eboshi volcanoes migrated towards the ESE after ca. 0.3 Ma and formed a volcanic chain oriented WNW–ESE.
