鉱物の熱発光から熱源位置を求めるインバージョン解析： 秋田県三途川カルデラ南部域での適用例

抄録

Geologically geothermal exploration was carried out in the Sanzugawa caldera (late Miocene to Pleistocene) located at the west side of the Kurikoma volcano in Northeast Japan. Several calderas with high internal temperatures were distributed around the Kurikoma volcano, particularly the southern part of the Sanzugawa caldera indicates significant geothermal manifestations such as hot springs and hydrothermal alteration. Hydrothermal alteration minerals were identified by X-ray powder diffraction, and thermoluminescence (TL) of quartz was measured for samples collected along rivers with mostly 500 m intervals. The study area was affected by several types of hydrothermal alteration such as sericite-montmorillonite, kaolinite, and laumontite alterations. The results of TL analysis revealed that the thermally affected area was closely related to the low resistivity zone identified by MT measurement. A strong correlation was recognized between spatial distance from the center point of low resistivity zone and TL intensity of samples in sericite-montmorillonite hydrothermal alteration and non-altered zones. Inversion calculation based on TL intensity indicated potential position of the heat source, which was coincident with the central point of low resistivity zone. This analytical method described here may estimate possible location of subsurface heat sources by TL geothermal exploration by samples obtained at the surface.