Mushroom Structure Revealed by Fluid Inclusion Thermometry in the Otake Geothermal Field, Japan

Abstract

Homogenization temperatures of fluid inclusions in quartz, anhydrite and calcite from the Otake geothermal field, Kyushu, Japan, have been measured. The minimum homogenization temperature at each depth seems to be almost equal to the present subsurface temperature. The Otake reservoir temperature at depths of 300-400 m is estimated to have been in the range of 200-220°C. The distribution patterns of homogenization temperatures suggest that the systems had cooled down as much as 15-30°C form the maximum state, whose temperatures are the same as the boiling point curve form the surface. The subsurface thermal profile obtained from the minimum inclusion temperature is mushroom shaped and slightly distorted due to an inclined up flow of hot water.