Thermochronology of hydrothermal alteration zones in the Kii Peninsula, southwest Japan; An Attempt for detecting the thermal anomalies and implications to the regional exhumation history

Sueoka, Shigeru; Iwano, Hideki*; Danhara, Toru*; Niwa, Masakazu; Kanno, Mizuho; Kohn, B. P.*; Kawamura, Makoto; Yokoyama, Tatsunori; Kagami, Saya; Ogita, Yasuhiro; et al.

Earth, Planets and Space (Internet), 75(1), p.177_1 - 177_24, 2023/12

https://doi.org/10.1186/s40623-023-01921-5

Fluid-inclusion and thermochronometric analyses have been applied to hydrothermal alteration zones and their host rocks outcropping in the Hongu area of the Kii Peninsula, southwestern Japan in an attempt to detect thermal anomalies related to hydrothermal events and quantify the thermal effects on the host rocks. Hydrothermal events at ca 150 deg. C and ca 200 deg. C were identified by fluid-inclusion microthermometry of quartz veins in the alteration zones. For the host rocks and alteration zones, in the youngest population zircon yielded U-Pb dates ranging between ca 74.7-59.2 Ma, fission-track dates of ca 27.2-16.6 Ma, and (U-Th)/He single-grain dates of ca 23.6-8.7 Ma. Apatite yielded pooled fission-track ages of ca 14.9-9.0 Ma. The zircon U-Pb dates constrain the maximum depositional ages of the sedimentary samples. However, the fission-track and (U-Th)/He dates show no clear trend as a function of distance from the alteration zones. Hence, no thermal anomaly was detected in the surrounding host rocks based on the thermochronometric data patterns. The fission-track and (U-Th)/He dates are rather thought to record regional thermal and exhumation histories rather than a direct thermal imprint of fluid flow, probably because the duration of such activity was too short or because fluid flow occurred before regional cooling events and were later thermally overprinted. Apatite fission-track ages of ca 10 Ma may reflect regional mountain uplift and exhumation related to the obduction of the SW Japan lithospheric sliver onto the Shikoku Basin, or the rapid subduction of the Philippine Sea slab associated with the clockwise rotation of the Southwest Japan Arc.

Research plan on geosphere stability for long-term isolation of radioactive waste (Scientific program for fiscal year 2023)

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.

LA-ICPMS U-Pb dating of zircon in paleotsunami deposits from Miyazaki plain, southwest Japan

Watanabe, Takahiro; Kagami, Saya; Yokoyama, Tatsunori; Niwa, Masakazu

Chigaku Zasshi, 132(4), p.353 - 361, 2023/08

https://doi.org/10.5026/jgeography.132.353

U-Pb dating of detrital zircons in paleotsunami deposits from the 1662 CE Kanbun-Hyuganada sea earthquake, Miyazaki plain on the Pacific coast of southwest Japan, was performed by a laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-ICPMS) system at Tono Geoscience Center, Japan Atomic Energy Agency. Twenty-five zircon grains were separated from the paleotsunami deposits by chemical abrasion and analyzed by the LA-ICPMS. U-Pb ages of the detrital zircons showed from ca. 14 Ma to 2405 Ma, and the age spectrum revealed high relative probability values around ca. 100 Ma and 2000 Ma. Detrital zircons with the age of ca. 100 Ma in the 1662 CE paleotsunami deposits could be partly originated from the Shimanto supergroup in southwest Japan. Moreover, the age spectrum of detrital zircons with Precambrian grains from the paleotsunami deposits was similar with those of fore-arc sandstones from central Kyushu Island.

Zircon U-Pb-Hf Isotopes and Whole-rock Geochemistry of Rhyolite and Tuff from the Harachiyama Formation, North Kitakami Mountains, NE Japan

Harada, Takuya*; Nagata, Mitsuhiro; Ogita, Yasuhiro; Kagami, Saya; Yokoyama, Tatsunori

Chigaku Zasshi, 132(1), p.57 - 65, 2023/02

https://doi.org/10.5026/jgeography.132.57

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.

Estimation of thermal/denudation histories in the Tanigawa-dake area based on thermochronological methods

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

Solidification pressures and ages recorded in mafic microgranular enclaves and their host granite; An Example of the world's youngest Kurobegawa granite

Suzuki, Kota*; Kawakami, Tetsuo*; Sueoka, Shigeru; Yamazaki, Ayu*; Kagami, Saya; Yokoyama, Tatsunori; Tagami, Takahiro*

Island Arc, 31(1), p.e12462_1 - e12462_15, 2022/09

https://doi.org/10.1111/iar.12462

Low-temperature thermochronology of active arc-arc collision zone, South Fossa Magna region, central Japan

Sueoka, Shigeru; Kobayashi, Yumi*; Fukuda, Shoma; Kohn, B. P.*; Yokoyama, Tatsunori; Sano, Naomi*; Hasebe, Noriko*; Tamura, Akihiro*; Morishita, Tomoaki*; Tagami, Takahiro*

Tectonophysics, 828, p.229231_1 - 229231_17, 2022/04

https://doi.org/10.1016/j.tecto.2022.229231

The South Fossa Magna zone, central Japan, has been an active collision zone between the Honshu Arc and the Izu-Bonin Arc since the middle Miocene and provides an excellent setting for reconstructing the earliest stages of continent formation. Multi-system geo-thermochronometry was applied to different domains of the South Fossa Magna zone, together with some previously published data, to reveal mountain formation processes, i.e., vertical crustal movements. Nine granitic samples yielded zircon U-Pb ages of 10.2-5.8 Ma ( = 2), apatite (U-Th)/He (AHe) ages of 42.8-2.6 Ma ( = 7), and apatite fission-track (AFT) ages of 44.1-3.0 Ma ( = 9). Thermal history inversion modeling based on the AHe and AFT data suggested rapid cooling events confined within the study region at 6-2 Ma. The Kanto Mountains may have undergone a domal uplift in association with their collision with the Tanzawa Block at 5 Ma. However, this uplift may have slowed down following the migration of the plate boundary and late Pliocene termination of the Tanzawa collision. The Minobu Mountains and possibly adjacent mountains may have been uplifted by the motional change of the Philippine Sea plate at 3 Ma. Therefore, the mountain formation in the South Fossa Magna zone was mainly controlled by collisions of the Tanzawa and Izu Blocks and motional change of the Philippine Sea plate. Earlier collisions of the Kushigatayama Block at 13 Ma and Misaka Block at 10 Ma appeared to have had little effect on mountain formation. Together with a 90 deg. clockwise rotation of the Kanto Mountains at 12-6 Ma, these observations suggest that horizontal deformation predominated during the earlier stage of arc-arc collision, and vertical movements due to buoyancy resulting from crustal shortening and thickening developed at a later stage.

Estimation of denudation history of the Kitakami Mountains based on apatite fission-track thermochronology

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.

Annual report for research on geosphere stability for long-term isolation of radioactive waste in fiscal year 2020

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.

Analytical method for chemical compositions of volcanic glasses in Tono Geoscience Center; Quantitative measurements of Major Elements by using EPMA and Minor Elements by LA-ICP-MS

Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*

JAEA-Testing 2021-001, 49 Pages, 2021/08

JAEA-Testing-2021-001.pdf:3.86MB

To make a contribution to safety assessment for geological disposal of high level radioactive and/or TRU waste, we need to assess long-term stability of geological environment and predict long-term changes of geotectonic events that will occur in the future, especially for Quaternary period ( 2.6 million years ago-present). In the most case, we investigate chronological data of geological events by radiometric dating. When some geological samples have no objects to which radiometric dating method can be applied (e.g., zircon, biotite, wood fragments and plant residues), we can use tephrochronology, which is geological dating method using each layer of tephra (erupted volcanic ash), for dating of geological layers. This chronological method is essential in Japan, where volcanism is very active. Tephra is usually characterized by petrographic characteristics and/or chemical composition (mainly major elements) of volcanic glasses and/or minerals in tephra. In Tono Geoscience Center (Japan Atomic Energy Agency), we develop an analytical technique of chemical composition including trace elements of volcanic glasses for detailed tephra identification. In this paper, we report a sample preparation procedure and analytical methods of chemical compositions of individual volcanic glass shards by using an electron probe microanalyzer and a laser ablation-inductively coupled plasma-mass spectrometer.