5:15 PM - 6:45 PM
[SVC28-P12] The geothermal exploration by quartz Thermoluminescence in the western part of the Hachimantai area
Keywords:geothermal expolation, Sengan geothermal area, Thermoluminescence, Field work, Simulation, XRD mineral identification
Thermoluminescence (TL) is a phenomenon in which energy stored by radiation is released as luminescence due to heat. Therefore, rocks collected from geothermal areas can be subjected to thermoluminescence indoors, and the intensity of the luminescence (TL intensity) can be analyzed to evaluate the thermal effects on the rocks (Tsuchiya et al., 2000, Tsuchiya et al., 2016). In this study, the TL method was used to evaluate the location of the thermal source for quartz in the western Hachimantai area upstream of the Tamagawa River.
In the Paleotamagawa caldera in the western Hachimantai area, the study area, the Aniai Formation of Neogene age, the Paleotamagawa Welded Tuff of Neogene age, and the Tamagawa Welded Tuff are distributed from the lower part. In addition to the Paleo-Tamagawa Tuff and Tamagawa Tuff, the Kanto-no-sawa Formation, which is composed of tuff, is widely distributed on the ground surface in this area, and sampling was conducted mainly in these formations. Subsequently, hydrothermal alteration minerals were examined and TL measurements were made. Based on these results, we attempted to estimate the location of the heat source by inversion analysis.
Pyrite was locally distributed around the Bunasawa area in the western part of the area, and laumontite was locally distributed around the Miharinoyu Hot Spring in the southern part of Akita Yakeyama, while clinoptilolite and montmorillonite, low-temperature to intermediate-temperature hydrothermal alteration minerals, were widely distributed in other areas.
Next, based on the results of the TL measurements, TL intensity was locally lower in areas where high-temperature hydrothermally altered minerals were distributed, and TL intensity varied over a wide area in areas where low-temperature-medium-temperature hydrothermally altered minerals were distributed. Based on these results, TL inversion analysis was performed using samples that were considered to have been subjected to broad-area thermal effects, excluding samples that were considered to have been locally hydrothermally altered.
For samples within a certain distance (hereinafter referred to as the extraction radius) from the assumed three-dimensional heat source location in the subsurface of the target area, we estimated the candidate heat source locations where the TL intensity correlates well with the distance from the assumed heat source location. We compared the results with MT survey results (Tokyo Institute of Technology - Tohoku University, 2017) in the same range and obtained the candidate heat source positions that are harmonic with MT survey results when the extraction radius is set to 9 km.
In the Paleotamagawa caldera in the western Hachimantai area, the study area, the Aniai Formation of Neogene age, the Paleotamagawa Welded Tuff of Neogene age, and the Tamagawa Welded Tuff are distributed from the lower part. In addition to the Paleo-Tamagawa Tuff and Tamagawa Tuff, the Kanto-no-sawa Formation, which is composed of tuff, is widely distributed on the ground surface in this area, and sampling was conducted mainly in these formations. Subsequently, hydrothermal alteration minerals were examined and TL measurements were made. Based on these results, we attempted to estimate the location of the heat source by inversion analysis.
Pyrite was locally distributed around the Bunasawa area in the western part of the area, and laumontite was locally distributed around the Miharinoyu Hot Spring in the southern part of Akita Yakeyama, while clinoptilolite and montmorillonite, low-temperature to intermediate-temperature hydrothermal alteration minerals, were widely distributed in other areas.
Next, based on the results of the TL measurements, TL intensity was locally lower in areas where high-temperature hydrothermally altered minerals were distributed, and TL intensity varied over a wide area in areas where low-temperature-medium-temperature hydrothermally altered minerals were distributed. Based on these results, TL inversion analysis was performed using samples that were considered to have been subjected to broad-area thermal effects, excluding samples that were considered to have been locally hydrothermally altered.
For samples within a certain distance (hereinafter referred to as the extraction radius) from the assumed three-dimensional heat source location in the subsurface of the target area, we estimated the candidate heat source locations where the TL intensity correlates well with the distance from the assumed heat source location. We compared the results with MT survey results (Tokyo Institute of Technology - Tohoku University, 2017) in the same range and obtained the candidate heat source positions that are harmonic with MT survey results when the extraction radius is set to 9 km.