Thermodynamic framework of the contact metamorphism around the Kakkonda granite in a active geothermal field, northeast Japan

摘要

Contact metamorphism, up to the andalusite isograd, around a Quaternary granite complex was examined by chemical equilibrium calculation for rock samples from the WD-la well in the Kakkonda geothermal area, northeast Japan. We have calculated metamorphic mineral assemblages for the bulk chemical composition of five core samples from 300° to 800°C and from 521 to 851 bar using the Gibbs free energy minimization method. Stability temperature ranges of the metamorphic minerals and their possible reactions for isograd are obtained, and the calculated results are consistent with those observed in the well. The estimated peak metamorphic temperature is about 200°C higher than the present temperature.