Development of research technique for the activity of magma and high-temperature fluid in the deeper part beneath the Japan arcs

Ninomiya, Atsushi

Geothermal activity is originated from magma or hot rock beneath the Quaternary volcanoes. High-temperature hot springs distribute around Iide Mountains showing high heat discharge values although the area is a nonvolcanic region of the Northeast Japan Arc. In this study, Iide Mountains were imaged by wide-band magnetotelluric soundings. A two-dimensional model shows that anomalous conductive body is clearly visible beneath the Iide Mountains. The location of the conductive body correlates with high-temperature hot springs of high He/He ratio. The temperature of the conductive body is estimated as above 400 C on the basis of thinning of the brittle seismogenic layer. We conclude that the conductor reflects the presence of partial melts in the crust, related to renewed magmatism in the present-day subdction system.