| Title | Alternative Geothermal Heat Sources Besides the Youngest Volcanism Related Magma Chamber--Examples in the Hohi and the Sengan Geothermal Areas in Japan |
|---|---|
| Authors | Tamanyu, Shiro |
| Year | 1991 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Exploration; Japan; Beppu-Kuju; Exploratory Well; Gravity Survey; Geologic Models; Magma; Temperature Gradient; Volcanic Front; Meteoric Water; Hydrothermal Circulation |
| Abstract | Many bore hole data in the Hohi and the Sengan geothermal areas proved that subsurface high temperature zones extend no only under the youngest volcanic zone but also pretty far behind the volcanic zone. These data suggest that other geothermal heat sources besides the youngest volcanism related magma chambers are expected. The high temperature pre Tertiary basement below the older volcanism (0.3-0.6 Ma) is expected as alternative potential heat source in the Hohi area. It might be interpreted that extra heat supply have been still continued after the magma injection of the older volcanism. On the other hand, the young granitic intrusive bodies are expected as potential heat source in the Sengan area. It might be interpreted that these bodies were intruded at very young period and have still kept high residual heat potential. Subsurface high temperature zones are also concordant with high gravity anomaly zones. It should be interpreted that high gravity anomaly zones are correlated with shallow pre Tertiary basement where cooling effect by meteoric water is less than low gravity anomaly zones. And also magma injection and granitic intrusion usually tend to make the pre Tertiary basement raise up. It should be given more careful consideration on the geothermal exploration of the potential area related to relatively old volcanism an young granitic intrusive bodies with high gravity anomaly zones. |