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Umeda, Koji; Asamori, Koichi; Ninomiya, Atsushi; Kanazawa, Sunao; Oikawa, Teruki
Journal of Geophysical Research, 112(B5), p.B05207_1 - B05207_9, 2007/05
It has been recognized that the Iide Mountains in Northeast Japan are unique because of their occurrence in a non-volcanic region yet hot springs have anomalously high heat discharge values similar to the heart discharge from hot springs in volcanic regions. In order to attempt to constrain the heat source of hydrothermal activity in the region, new helium isotopic data from hot springs surrounding the Iide Mountains was obtained. The 
He/
He ratios of the hot spring gases sampled range from 0.22 to 7.9 RA, and the highest ratio is similar to MORB-type helium (8 
1 RA), indicating a significant contribution of primordial mantle-derived helium. Estimation of post-intrusive radiogenic ingrowth of He by decay of U and Th suggests that the heat source beneath the Iide Mountains is not likely ancient magma intruded in the Middle Miocene but newly ascending magma derived from mantle material. The geographical distribution of He/He ratios of hot spring gases reveals that crustal magma storage exists beneath the Kitamata-dake, one of the peaks of the Iide Mountains. This can be used to interpret the geophysical anomalies in this region such as crustal seismicity and results of magnetotelluric imaging.
He/He ratios of hot springs on Shikoku Island, Southwest JapanUmeda, Koji; Kanazawa, Sunao; Kakuta, Chifumi*; Asamori, Koichi; Oikawa, Teruki
Geochemistry, Geophysics, Geosystems (Internet), 7(4), p.Q04009_1 - Q04009_11, 2006/04
New helium isotopic data from hot springs on Shikoku Island with much denser sampling than previous studies were obtained, in order to elucidate the geographical distribution of He/He ratios in the fore-arc regions of Southwest Japan. Systematic, regional variations in He/He ratios were observed on both Sikoku Island and the Kii Peninsula. Most of the hot springs having He/He ratios in the range 1.0 RA to 2.0 RA were determined throughout Shikoku Island. On the other hand, the majority of hot springs in the Kii Peninsula have He/He ratios higher than 2.0 RA. It has been suggested by some authors that the anomalously high He/He ratios in the fore-arc region of Southwest Japan are related to the migration of mantle-derived helium with aqueous fluids generated by dehydration of the subducting PHS and mixing with terrestrial waters [e.g., Matsumoto et al., 2003]. According to recent seismological observations of crustal microearthquakes and their focal mechanisms, the geotectonic environment beneath Shikoku Island is subject to a stress field without normal faulting and the extremely low crustal seismicity, which does not favor migration of aqueous fluids from the subcrustal lithosphere, resulting in a relatively small influence of MORB-type helium at surface. As a consequence, the regional variation in He/He ratios of hot springs on Shikoku Island are interpreted as a three-component mixture of mantle-derived helium associated with magmatism of Middle Miocene of age (
3.4 RA), crustal, radiogenic helium and atmospheric helium.
Oikawa, Teruki; Umeda, Koji; Kanazawa, Sunao; Matsuzaki, Tatsuji*
Journal of Mineralogical and Petrological Sciences, 101(1), p.23 - 28, 2006/02
Times Cited Count：2 Percentile：4.3(Mineralogy)The authors report biotite K-Ar, zircon FT, and apatite FT ages from four sites in the Ichifusayama Granodiorite in the Outer Zone acidic rocks of Southwest Japan, Southern Kyushu. All the K-Ar ages and FT ages are concentrated on 13-10Ma. The difference in the apatite FT ages was caused by an influence of paleotopography such as a deep valley. The rapid cooling of the granodiorite in ca. 13 Ma occurred by uplift throughout the Outer Zone of Southwest Japan in Kyushu. It is considered that obduction to the Philippine Sea Plate of the Outer Zone of Kyushu also occurred in ca. 13 Ma. It is considered that obduction to the Philippine Sea Plate of the Outer Zone of Kyushu also occurred in ca. 13 Ma.
He/He ratios in gases in JapanKanazawa, Sunao; Asamori, Koichi; Umeda, Koji; Shimada, Koji
no journal, ,
no abstracts in English
Yamada, Nobuto; Suzuki, Keiichi*; Kanazawa, Sunao*; Tsuge, Takashi*
no journal, ,
To evaluate the distribution of geological discontinuity such as fractures around the underground gallery is one of the important factors to conduct high level radioactive waste disposal, but it is difficult to evaluate them enough only by geological survey such as boring investigations. We carried out GPR to obtain the distribution of fractures exist nearby the underground gallery of granite in Mizunami Underground Research Laboratory, and understand that we can detect them by GPR.
Yamada, Nobuto; Sasao, Eiji; Suzuki, Keiichi*; Kuboshima, Koji*; Kanazawa, Sunao*
no journal, ,
JAEA and KGE perform the joint research on cosmic ray muons applying detection of sub-surface geological structure such as fault, using the research gallery of the Mizunami Underground Research Laboratory. We set the detectors of cosmic ray muons in the underground gallery to evaluate its applicability for estimating geological structure in deep underground. We estimate the geological structure by the number of cosmic ray muons observed from November 2013 to August 2014 and confirm that we can observe the substantial number of cosmic ray muons to estimate the geological structure in the research gallery of granite at -300m underground.
