9:00 AM - 10:30 AM
[SVC30-P07] Topographic Interpretation for Fault Mapping Using Stereoscopic Images and Zircon Fission-track Dating in Western Kuju Volcano
Keywords:Otake-Hatchobaru geothermal system, Tectonic geomorphology, Topographic interpretation using stereoscopic images, Fission-track dating, Heat soruce of geothermal system
The major geologic structure controlling geothermal fluid flow in the Otake-Hatchobaru geothermal fields are NW-SE trending fault system (Hayashi, 1985; Matsumoto et. al. 1989). Whereas E-W trending normal fault system are dominant in terms of recent active tectonic structure in Beppu-Shimabara Graben where the Otake-Hatchobaru fields are included (Imaizumi et al. 2018). Wulaningsih et al. (2021) revealed that the E-W trending fractures are superior in the borehole walls of reinjection wells drilled in the Otake field. Based on this observation, the fissures by E-W trending faults are estimated to control geothermal fluid flow in the Otake field (Wulaningsih et al. 2021) in addition to those by NW-SE trending faults.
Our project aims refine geological structural model and geothermal conceptual model in Western Kuju Volcano including the Otake-Hatchobaru geothermal system where geothermal power plants with 126.5 MW output capacity in total have been operating. We present here results of topographic interpretation for updating faults trace map and volcanological sequence. In addition, we report result of zircon fission-track dating of volcanic rocks in Western Kuju Volcano.
We performed topographic interpretation using stereoscopic images prepared from 5 m digital elevation model offered by Geospatial Information Authority of Japan. Stereoscopic images are prepared by TAC Engineering Co. Ltd. As a result, fault scarps, alignment of saddles and topographic lineaments orienting E-W to WNW-ESE directions are recognized at the volcanic edifices of Mt. Kuroiwasan, Mt. Gotosan and Mt. Ryoshiyama Volcanoes. Those are interpreted as geomorphologically active tectonic features. Both hydrothermally altered ground and discharging of fumarolic gases emerge just along the above active fault traces. These data and borehole imaging analysis shown by Wulaningsih et al. (2021) suggest that E-W to WNW-ESE trending active tectonic structures is one of the important geologic structures controlling geothermal fluid flow in Western Kuju Volcano.
Through stereoscopic topographic interpretation, we newly identified morphological features showing volcanic dome and lava flow deposits. These topographies are assumed to be a volcanic product of post-volcanic activity of Mt. Kuroiwasan Volcano which is categorized into Kuju Volcano’s Stage 1 activity ranging between 200ka to 54ka (Kawanabe et al. 2015). To determine age of the volcanic dome, we have collected volcanic rock materials in the field and dated using zircon fission-track technique adopting LA-ICP-MS-FT method. As relatively young fission-track age is expected, we sampled 1408 zircon grains to improve dating accuracy. The obtained age is 0.027±0.008Ma, which is younger than the age of Kuju Volcano’s Stage 1 activity. Aizawa et al. (2021) imaged the presence of subvertical conductors at 2-6 km depth at the east of Mt. Kuroiwasan Volcano. The edges of the subvertical conductor were assumed to play the role for magmatic fluid passway from the deeper area to near surface (Aizawa et al. 2021). This interpretation leads us to the understanding that volcanic activities had been continuous around Mt. Kuroiwasan Volcano. Thus, the heat source of geothermal system of the Otake-Hatchobaru has been originated from the succeeding volcanic activity of Mt. Kuroiwasan Volcano. For better understating of the relation between geologic features and heat source of geothermal system in Western Kuju Volcano, high resolution field mapping of faults and precise age control by tephrochronology are necessary in the future.
Acknowledgments: Zircon fission-track dating is supported by New Energy and Industrial Technology Development Organization (NEDO) (Potential survey and estimation of power generation of supercritical geothermal resources in East Japan and Kyushu, Japan).
Our project aims refine geological structural model and geothermal conceptual model in Western Kuju Volcano including the Otake-Hatchobaru geothermal system where geothermal power plants with 126.5 MW output capacity in total have been operating. We present here results of topographic interpretation for updating faults trace map and volcanological sequence. In addition, we report result of zircon fission-track dating of volcanic rocks in Western Kuju Volcano.
We performed topographic interpretation using stereoscopic images prepared from 5 m digital elevation model offered by Geospatial Information Authority of Japan. Stereoscopic images are prepared by TAC Engineering Co. Ltd. As a result, fault scarps, alignment of saddles and topographic lineaments orienting E-W to WNW-ESE directions are recognized at the volcanic edifices of Mt. Kuroiwasan, Mt. Gotosan and Mt. Ryoshiyama Volcanoes. Those are interpreted as geomorphologically active tectonic features. Both hydrothermally altered ground and discharging of fumarolic gases emerge just along the above active fault traces. These data and borehole imaging analysis shown by Wulaningsih et al. (2021) suggest that E-W to WNW-ESE trending active tectonic structures is one of the important geologic structures controlling geothermal fluid flow in Western Kuju Volcano.
Through stereoscopic topographic interpretation, we newly identified morphological features showing volcanic dome and lava flow deposits. These topographies are assumed to be a volcanic product of post-volcanic activity of Mt. Kuroiwasan Volcano which is categorized into Kuju Volcano’s Stage 1 activity ranging between 200ka to 54ka (Kawanabe et al. 2015). To determine age of the volcanic dome, we have collected volcanic rock materials in the field and dated using zircon fission-track technique adopting LA-ICP-MS-FT method. As relatively young fission-track age is expected, we sampled 1408 zircon grains to improve dating accuracy. The obtained age is 0.027±0.008Ma, which is younger than the age of Kuju Volcano’s Stage 1 activity. Aizawa et al. (2021) imaged the presence of subvertical conductors at 2-6 km depth at the east of Mt. Kuroiwasan Volcano. The edges of the subvertical conductor were assumed to play the role for magmatic fluid passway from the deeper area to near surface (Aizawa et al. 2021). This interpretation leads us to the understanding that volcanic activities had been continuous around Mt. Kuroiwasan Volcano. Thus, the heat source of geothermal system of the Otake-Hatchobaru has been originated from the succeeding volcanic activity of Mt. Kuroiwasan Volcano. For better understating of the relation between geologic features and heat source of geothermal system in Western Kuju Volcano, high resolution field mapping of faults and precise age control by tephrochronology are necessary in the future.
Acknowledgments: Zircon fission-track dating is supported by New Energy and Industrial Technology Development Organization (NEDO) (Potential survey and estimation of power generation of supercritical geothermal resources in East Japan and Kyushu, Japan).