Fission Track Age of Volcanoes in the Kuju Volcanic Region in Relation to Geothermal Activity

In order to clarify the relation between volcanic and geothermal activities in the Hohi geothermal area, fission track ages of the Kuju volcanic rocks, characterized by hornblende andesite, have been measured. The results show that the Kuju volcanism began about 0.3 Ma ago and continued to several tens thousand years ago. The most active Type A geothermal fields are associated with volcanoes younger than 0.20 Ma, the active Type B fields with those from 0.15 to 0.30 Ma in most cases. The volumes of these volcanoes range from 0.3 to 3.2 km³. Larger volcanoes tend to cool down more slowly than smaller ones.