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Nakajima, Toru; Sueoka, Shigeru; Nagata, Mitsuhiro; Kohn, B. P.*; Ramos, N. T.*; Tsutsumi, Hiroyuki*; Tagami, Takahiro*
Earth, Planets and Space (Internet), 75(1), p.176_1 - 176_11, 2023/12
Times Cited Count：0 Percentile：1.28(Geosciences, Multidisciplinary)Geo- and thermochronological methods were applied to dioritic rocks from the Cordillera Central, Luzon, Philippines, to understand their emplacement and exhumation history in the island arc mountains. Zircon U-Pb ages range from 32.54 
0.70 to 6.11 0.15 (2SE) Ma, indicating that dioritic magmas intruded the middle and upper crust intermittently during Tertiary magmatism. Zircon fission-track (ZFT) pooled ages range from 35.63 2.17 to 6.91 0.36 (2SE) Ma, and are generally comparable with the U-Pb ages at each locality. These results suggest that the diorites cooled rapidly below 250-350 degree, (i.e. through the partial annealing zone of the ZFT system), following their intrusion. On the other hand, the zircon and apatite (U-Th-Sm)/He (ZHe and AHe) weighted mean ages, ranging from 11.71 0.36 to 8.82 0.26 and 9.21 0.52 to 0.98 0.088 (2SE) Ma respectively, indicate a decrease in cooling rates at a lower temperature range, especially through the partial retention zone of the AHe system. This observation suggests that the ZFT ages reflect initial cooling of the dioritic magma, whereas the AHe ages reflect the cooling history associated with regional exhumation following the initial cooling phase. Spatial distribution of the AHe ages suggest that rapid exhumation of the Cordillera Central during the Quaternary resulted from the block-like uplift of the entire mountain range.
Sueoka, Shigeru; Kawakami, Tetsuo*; Suzuki, Kota*; Kagami, Saya; Yokoyama, Tatsunori; Shibazaki, Bunichiro*; Nagata, Mitsuhiro; Yamazaki, Ayu*; Higashino, Fumiko*; King, G. E.*; et al.
Fisshion, Torakku Nyusureta, (36), p.1 - 3, 2023/12
no abstracts in English
Nakajima, Toru; Nagata, Mitsuhiro; Fukuda, Shoma; Sueoka, Shigeru
Chishitsugaku Zasshi (Internet), 129(1), p.503 - 507, 2023/11
Zircon U-Pb dating was carried out on granitic rocks from plutons in the Taiheizan Complex in Akita Prefecture, NE Japan. Two granodiorites from the Main Intrusive Rocks yielded weighted mean 206Pb/238U dates of 103.41.0 Ma and 115.61.1 Ma (1SE). Three porphyrygranite from the Young Intrusive Rocks yielded weighted mean 206Pb/238U dates of 11.40.1 Ma, 4.70.1Ma, and 4.80.1 Ma (1SE). The older and younger dates can be interpreted as the ages of early and later stages of granitic intrusion at the sampling locations. The Pliocene U-Pb dates suggest that the Nibetsu Body in the Young Intrusive Rocks is one of the youngest granitic plutons currently exposed on Earth.
Niwa, Masakazu; Shimada, Koji; Sueoka, Shigeru; Fujita, Natsuko; Yokoyama, Tatsunori; Ogita, Yasuhiro; Fukuda, Shoma; Nakajima, Toru; Kagami, Saya; Ogata, Manabu; et al.
JAEA-Review 2023-017, 27 Pages, 2023/10
JAEA-Review-2023-017.pdf:0.94MB
This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency (JAEA), in fiscal year 2023. The objectives and contents in fiscal year 2023 are described in detail based on the JAEA 4th Medium- and Long-term Plan (fiscal years 2022-2028). In addition, the background of this research is described from the necessity and the significance for site investigation and safety assessment, and the past progress. The plan framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques.
Niwa, Masakazu; Shimada, Koji; Sueoka, Shigeru; Ishihara, Takanori; Ogawa, Hiroki; Hakoiwa, Hiroaki; Watanabe, Tsuyoshi; Nishiyama, Nariaki; Yokoyama, Tatsunori; Ogata, Manabu; et al.
JAEA-Research 2023-005, 78 Pages, 2023/10
JAEA-Research-2023-005.pdf:6.51MB
This annual report documents the progress of research and development (R&D) in the 1st fiscal year of the Japan Atomic Energy Agency 4th Medium- and Long-term Plan (fiscal years 2022-2028) to provide the scientific base for assessing geosphere stability for long-term isolation of high-level radioactive waste. The plan framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques. The current status of R&D activities with previous scientific and technological progress is summarized.
Kubomi, Ko*; Nagata, Mitsuhiro; Ota, Hiroto*; Miyata, Kazunori*; Oto, Shigeru*
Chishitsugaku Zasshi (Internet), 129(1), p.453 - 460, 2023/09
The Hakobuchi Formation in Hokkaido, NE Japan, consists of marine to terrestrial clastic rocks of the uppermost part of the Yezo Group, was previously interpreted to range from Early Campanian to Late Paleocene age, with a hiatus near the K/Pg boundary. No definitive evidence of the depositional age indicating Lower Paleocene (Danian) has been reported from the formation so far. We reported the LA-ICPMS zircon U-Pb dates of a tuff layer of the Hakobuchi Formation in the Yubari area. The weighted average date of the youngest cluster was 64.1 1.1 Ma (2
), suggesting the depositional age of the formation is Danian. The result is the first radiometric evidence indicating that the Hakobuchi Formation, at least partly, is correlated with the Danian, and is essential to discuss the depositional age of the Hakobuchi Formation and geochronology of the Yezo Group.
Bando, Koki*; Nagata, Mitsuhiro; Asahara, Yoshihiro*; Ishizaki, Yasuo*; Oto, Shigeru*
Shimonitamachi Shizenshikan Kenkyu Hokoku, (8), p.33 - 53, 2023/03
We studied the geochronology and geochemistry of the Cretaceous Atokura Formation called Atokura nappe and intrusive rocks in Shimonita, Gunma Prefecture. The depositional age of the Atokura Formation has not been determined whether it was the Early Cretaceous (Barremian) or Late Cretaceous (Cenomanian-Campanian). The youngest cluster dates obtained from 4 sandstone samples of the Atokura Formation are 182.8 Ma, 129.8 Ma, 123.7 Ma, and 115.1 Ma. Zircons from igneous rocks in the Atokura Formation yielded U-Pb ages of 123.2 Ma, and their zircons show 
Hf(t)=3.0 to 3.8. The depositional age of the Atokura Formation generally supported the Barremian, but younger zircon U-Pb date was obtained from one sample. The intrusive rocks are similar to the U-Pb dates and Hf isotopes of zircons obtained from Kitakami or Abukuma granitoids in NE Japan.
Harada, Takuya*; Nagata, Mitsuhiro; Ogita, Yasuhiro; Kagami, Saya; Yokoyama, Tatsunori
Chigaku Zasshi, 132(1), p.57 - 65, 2023/02
The Harachiyama Formation is Lower Cretaceous volcanic rocks, distributed in the eastern margin of the Kitakami Mountains in northeastern Japan. We performed whole-rock chemical analysis, zircon U-Pb dating and Hf isotope analysis from the Harachiyama Formation to constrain the formation age and discuss the origin of magma. The lava and tuff samples of the Harachiyama Formation from the Omoto and Tsukue areas support island-arc rhyolitic rocks (SiO
content 
70%), and yielded the weighted mean U-Pb ages of 127.8 3.4 Ma and 129.2 2.6 Ma (2), respectively. Eighteen zircon grains from two samples, dated between 141.6 Ma and 123.9 Ma, yielded positive Hf(t) values between +5.0 and +8.7. These ages and values are consistent with those of the Kitakami Granititods reported in previous studies. Therefore, it is suggested that the Harachiyama Formation have the same magmatic origin as the Kitakami Granitoid.
Nagata, Mitsuhiro; Nakajima, Toru; Fukuda, Shoma; Sueoka, Shigeru; Yagi, Koshi*; Yokoyama, Tatsunori
Fisshion, Torakku Nyusureta, (36), p.9 - 13, 2023/00
Zircon U-Pb and fission track (FT) dating and moonstone (sanidine) K-Ar dating of the Wassogatake Formation in the southern part of Hakusan City, Ishikawa Prefecture were carried out as part of the search for zircon standard materials for dating. The weighted average U-Pb dates obtained from the three samples are ca. 21.9-21.7 Ma, overlapping within the uncertainty range. Zircon FT and moonstone K-Ar dates were obtained younger ages from some samples. In addition, the track lengths of the three samples are short. Based on the above results, the zircons of the Wassogatake Formation are effective for the high closure temperature dating method (e.g., U-Pb dating), but are not suitable for the low closure temperature dating method (e.g., FT dating).
Nakajima, Toru; Fukuda, Shoma; Nagata, Mitsuhiro; Danhara, Toru*; Iwano, Hideki*; Sueoka, Shigeru
Fisshion, Torakku Nyusureta, (35), p.34 - 36, 2022/12
In this presentation, we report the results of fission-track etching experiments for the practical use of baddeleyite fission-track dating and a brief discussion of the results.
Minami, Saki*; Sueoka, Shigeru; Fukuda, Shoma; Nagata, Mitsuhiro; Kohn, B. P.*; Yokoyama, Tatsunori; Kagami, Saya; Kajita, Yuya*; Tagami, Takahiro*
Fisshion, Torakku Nyusureta, (35), p.22 - 26, 2022/12
no abstracts in English
Sasao, Eiji; Ishimaru, Tsuneari; Niwa, Masakazu; Shimada, Akiomi; Shimada, Koji; Watanabe, Takahiro; Sueoka, Shigeru; Yokoyama, Tatsunori; Fujita, Natsuko; Ogita, Yasuhiro; et al.
JAEA-Review 2022-022, 29 Pages, 2022/09
JAEA-Review-2022-022.pdf:0.97MB
This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency (JAEA), in fiscal year 2022. The objectives and contents in fiscal year 2022 are described in detail based on the JAEA 4th Medium- and Long-term Plan (fiscal years 2022-2028). In addition, the background of this research is described from the necessity and the significance for site investigation and safety assessment, and the past progress. The plan framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques
Nagata, Mitsuhiro; Fukuda, Shoma; Sueoka, Shigeru; Nakajima, Toru; Kajita, Yuya*; Minami, Saki*; Okamoto, Akira*; Tagami, Takahiro*
Fisshion, Torakku Nyusureta, (35), p.15 - 18, 2022/09
We performed U-Pb dating on zircons from the Utaosa Rhyolite of the Teragi Group as part of the search for standard materials for dating of zircons. Previous studies about Utaosa Rhyolite have reported ca. 2.30-2.77 Ma zircon fission track, zircon (U-Th)/He, and biotite K-Ar ages. U-Pb dating was carried out on the multi-collector inductively coupled plasma mass spectrometer with a laser ablation system. The weighted mean 
U-
Pb ages of 2.650.16 Ma and 2.660.15 Ma were obtained from two samples. These ages are consistent with the ages from the previous studies. Therefore the results show that zircons from the Utaosa Rhyolite may be effective as a standard material.
Sawada, Hikaru*; Niki, Sota*; Nagata, Mitsuhiro; Hirata, Takafumi*
Minerals (Internet), 12(1), p.107_1 - 107_15, 2022/01
Times Cited Count：2 Percentile：43.7(Geochemistry & Geophysics)The Oeyama ophiolite is one of the oldest components in Japanese Islands and important to reveal the initiation of plate subduction along proto-Japan. This study performed U-Pb-Hf isotopic and trace element analyses of zircon in gabbroic rocks. The weight mean of Pb/U dates from zircons of the Oeyama ophiolite is 544 4 Ma (2 sigma). Trace element analysis of the zircons exhibit that the host rock was derived from the mantle depleted of incompatible elements like mid-oceanic ridge basalt. The present igneous age and geochemical feature of the zircons is consistent with previous work for other part of the Oeyama ophiolite. Zircon Lu-Hf isotopic analysis also indicate that the gabbroic rock was derived from the depleted mantle domain. The Hf isotopic signature is more depleted than those of the zircons in jadeitite associated with the Oeyama ophiolite. This result implies that the older crustal material was involved into the initial oceanic plate subduction along the proto-Japan arc.
Minami, Saki*; Nagata, Mitsuhiro; Sueoka, Shigeru; Fukuda, Shoma; Kajita, Yuya*; Ogita, Yasuhiro; Kagami, Saya; Yokoyama, Tatsunori; Tagami, Takahiro*
Earth, Planets and Space (Internet), 73(1), p.231_1 - 231_7, 2021/12
Times Cited Count：1 Percentile：8.23(Geosciences, Multidisciplinary)Kajita, Yuya*; Sueoka, Shigeru; Fukuda, Shoma; Yokoyama, Tatsunori; Kagami, Saya; Nagata, Mitsuhiro; Tagami, Takahiro*
Fisshion, Torakku Nyusureta, (34), p.14 - 16, 2021/12
For reconstructing the uplift/denudation history of the fore-arc side of the NE Japan Arc on geologic timescales, U-Pb dating and apatite fission-track (AFT) thermochronometry were applied to granitoids in Kitakami mountains. In addition, U-Pb dating for the Jodogahama rhyolite at the easternmost Kitakami mountains was also carried out to estimate the timing of volcanism and its thermal effect. Consequently, U-Pb ages of 122.7 Ma and 117.3 Ma for 2 samples of the Cretaceous granites and AFT ages ranging from 156.8 Ma to 70.3 Ma of 15 samples were obtained. Concerning the Jodogahama rhyolite, U-Pb age of 44.3 Ma was obtained. Integrated AFT data of this study and previous ones in Kitakami mountains, the trend of ages shows younging toward west. Although such age trend can be explained by volcanism of the Jodogahama reflecting the migration of a paleo-volcanic front, all AFT ages exhibited significantly older than U-Pb data of the Jodogahama and the thermal inverse modeling based on track length distributions provided slow cooling patterns. These observations did not supported the reheating of volcanism as a cause of age trend. As future prospects, we are planning to improve the reliability of age data based on additional analyses and apply an ultra low-temperature thermochronometer, e.g., ESR method.
Minami, Saki*; Nagata, Mitsuhiro; Sueoka, Shigeru; Fukuda, Shoma; Kajita, Yuya*; Ogita, Yasuhiro; Yokoyama, Tatsunori; Kagami, Saya; Tagami, Takahiro*
Fisshion, Torakku Nyusureta, (34), p.4 - 8, 2021/12
This study employed U-Pb dating for determining the intrusive age of young (several Ma) granitoids in Tanigawa-dake area, where rapid and intense uplift/denudation has probably occurred in Japan. As results, U-Pb age of 109 Ma for the Cretaceous granodiorite and 3.95-3.19 Ma about 3 samples of the Pliocene granodiorites were obtained. These U-Pb ages showed consistent with previously reported ages based on thermochronometers having lower closure temperatures such as K-Ar or zircon fission-track methods. All previous data indicated younger ages than U-Pb ones in this study. Therefore, our U-Pb data can be interpreted as intrusive ages of young granitoids, inferring multiple events possibly occurred at least twice and contributed to the formation in young granitoids in the Tanigawa-dake area.
Ishimaru, Tsuneari; Ogata, Nobuhisa; Kokubu, Yoko; Shimada, Koji; Niwa, Masakazu; Shimada, Akiomi; Watanabe, Takahiro; Sueoka, Shigeru; Yokoyama, Tatsunori; Fujita, Natsuko; et al.
JAEA-Research 2021-007, 65 Pages, 2021/10
JAEA-Research-2021-007.pdf:4.21MB
This annual report documents the progress of research and development (R&D) in the 6th fiscal year during the JAEA 3rd Mid- and Long-term Plan (fiscal years 2015-2021) to provide the scientific base for assessing geosphere stability for long-term isolation of the high-level radioactive waste. The planned framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques. The current status of R&D activities with previous scientific and technological progress is summarized.
Noda, Atsushi*; Miyazaki, Kazuhiro*; Mizuno, Kiyohide*; Nagata, Mitsuhiro
GSJ Chishitsu Nyusu, 10(9), p.207 - 213, 2021/09
This paper is a brief explanation of the 1:50,000 Quadrangle Geological Map of "Ikeda". The geology of the Ikeda district which is located in the northern part of Shikoku, is divided into basement Late Cretaceous plutonic, metamorphic, and sedimentary rocks, and covering Post-Miocene volcanic and sedimentary rocks. This area is known for the distribution of the Median Tectonic Line, which is the major geological fault in Japan. This map is not only geologically important, but also important from a disaster prevention perspective.
Ishimaru, Tsuneari; Kokubu, Yoko; Shimada, Koji; Shimada, Akiomi; Niwa, Masakazu; Watanabe, Takahiro; Sueoka, Shigeru; Yokoyama, Tatsunori; Fujita, Natsuko; Ogita, Yasuhiro; et al.
JAEA-Review 2021-012, 48 Pages, 2021/08
JAEA-Review-2021-012.pdf:1.64MB
This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency (JAEA), in fiscal year 2021. The objectives and contents in fiscal year 2021 are described in detail based on the JAEA 3rd Medium- and Long-term Plan (fiscal years 2015-2021). In addition, the background of this research is described from the necessity and the significance for site investigation and safety assessment, and the past progress. The plan framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques.
