Simultaneous determination of zircon crystallisation age and temperature; Common thermal evolution of mafic magmatic enclaves and host granites in the Kurobegawa granite, central Japan

Yuguchi, Takashi*; Yamazaki, Hayato*; Ishibashi, Kozue*; Sakata, Shuhei*; Yokoyama, Tatsunori; Suzuki, Satoshi*; Ogita, Yasuhiro; Sando, Kazusa*; Imura, Takumi*; Ono, Takeshi*

Journal of Asian Earth Sciences, 226, p.105075_1 - 105075_9, 2022/04

https://doi.org/10.1016/j.jseaes.2021.105075

Simultaneous determination of the U-Pb age of zircon and concentration of titanium in a single analysis spot, using inductively coupled plasma mass spectrometry with laser ablation sample introduction, produces paired age and temperature data of zircon crystallisation, potentially revealing time-temperature () histories for evolved magma. The Kurobegawa granite, central Japan, contains abundant mafic magmatic enclaves (MMEs). We applied this method to evaluate MMEs and their host (enclosing) granites. Cooling behaviour common to both MMEs and host rocks was found between 1.5 and 0.5 Ma. Rapid cooling from the zircon crystallisation temperature to the closure temperature of biotite K-Ar system was within 1 million year. Combining the obtained paths of MMEs and host rocks with petrological information can provide insights into magma chamber processes. This suggests that MME flotation, migration, and spread through the magma chamber ceased at 1.5-0.5 Ma, indicating the emplacement age of the Kurobegawa granitic pluton, as no large-scale reheating episodes have occurred since then.

Simultaneous determination of zircon U-Pb age and titanium concentration using LA-ICP-MS for crystallization age and temperature

Yuguchi, Takashi*; Ishibashi, Kozue*; Sakata, Shuhei*; Yokoyama, Tatsunori; Ito, Daichi*; Ogita, Yasuhiro; Yagi, Koshi*; Ono, Takeshi*

Lithos, 372-373, p.105682_1 - 105682_9, 2020/11

https://doi.org/10.1016/j.lithos.2020.105682

Simultaneous determination of zircon U-Pb age and titanium concentration for a single analysis spot gives both the crystallization age and temperature. The crystallization age and temperature pairs in granitic zircons map the time-temperature () path of granitic magma before its solidification. In laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis, it is challenging to quantitatively analyse a low level of titanium concentration. This study employed two approaches using a Quadrupole mass spectrometer equipped with a collision/reaction cell (CRC). The methods were applied to zircon samples of the Kurobegawa granite (KRG), the Okueyama granite (OKG), the Toki granite (TKG), and the Tono plutonic complex (TPC) and provided U-Pb ages and titanium concentrations consistent with previous studies. The crystallization ages and temperatures collected from individual analysis spots of zircon samples in the KRG, OKG, TKG, and TPC are plotted in the diagrams and enable us to characterize the rapid cooling paths at thermal conditions of zircon crystallization at the sampling sites.

Role of micropores, mass transfer, and reaction rate in the hydrothermal alteration process of plagioclase in a granitic pluton

Yuguchi, Takashi*; Shobuzawa, Kaho*; Ogita, Yasuhiro*; Yagi, Koshi*; Ishibashi, Masayuki; Sasao, Eiji; Nishiyama, Tadao*

American Mineralogist, 104(4), p.536 - 556, 2019/04

https://doi.org/10.2138/am-2019-6786

This study describes the plagioclase alteration process with a focus on the role of micropores, mass transfer and reaction rate in the Toki granitic pluton, central Japan. The plagioclase alteration process involves albitization, K-feldspathization, and the formation of illite, calcite, fluorite and epidote. Such secondary minerals of hydrothermal origin in plagioclase within granitic rocks record the chemical characteristics of the hydrothermal fluid. Our results highlight (1) the nature of micropores such as distribution and volume in plagioclase, (2) the reaction nature of plagioclase alteration inferred by petrography and chemistry, (3) the physical conditions including alteration age and temperature, (4) the sequential variations of the fluid chemistry and (5) the mass transfer rate and reaction rate in the plagioclase alteration.

Spatial distribution of the apatite fission-track ages in the Toki granite, central Japan; Exhumation rate of a Cretaceous pluton emplaced in the East Asian continental margin

Yuguchi, Takashi*; Sueoka, Shigeru; Iwano, Hideki*; Danhara, Toru*; Ishibashi, Masayuki; Sasao, Eiji; Nishiyama, Tadao*

Island Arc, 26(6), p.e12219_1 - e12219_15, 2017/11

https://doi.org/10.1111/iar.12219

The spatial distribution of AFT age in the granitic body is a favorable key to reveal a cooling behavior of the whole pluton. The cooling behavior is attributable to the regional exhumation of the Toki granite related to the regional denudation of the Tono district. Combination of the AERs and AFT inverse model applying to the granite is a powerful procedure for evaluating the cooling and exhumation history of the granitic pluton and thus denudation history of the tectonic region that surrounded the rock body.

Long term behavior of hydrogeological structures associated with faulting; An Example from the deep crystalline rock in the Mizunami URL, Central Japan

Ishibashi, Masayuki; Yoshida, Hidekazu*; Sasao, Eiji; Yuguchi, Takashi*

Engineering Geology, 208, p.114 - 127, 2016/06

https://doi.org/10.1016/j.enggeo.2016.04.026

Damage zone (DS) formed by faulting in crystalline rocks can act as significant transport pathway. Therefore, this paper describes the features of WCFs and their long-term behavior associated with faulting based on the results of investigations at the GL -300m and -500m in the MIU. The results of detailed investigations in and around DZ indicate that there are three stages in the development of hydrogeological structures: 1st stage) the formation of background fractures; 2nd stage) the formation of a DZ and corresponding increase in the hydraulic permeability as a result of formation of small fractures; and 3rd stage) the formation of fracture fillings and the hydraulic permeability of the DZ decrease. In the late 3rd stage, unconsolidated clayey fillings formed associated with faulting resulting in decreased permeability of fractures in the DZ. These results underline the importance of understanding the development stages for evaluating the effect of faulting in orogenic belt plutons.

Mizunami Underground Research Laboratory Project, Annual report for fiscal year 2014

Hama, Katsuhiro; Mikake, Shinichiro; Ishibashi, Masayuki; Sasao, Eiji; Kuwabara, Kazumichi; Ueno, Tetsuro; Onuki, Kenji*; Beppu, Shinji; Onoe, Hironori; Takeuchi, Ryuji; et al.

JAEA-Review 2015-024, 122 Pages, 2015/11

JAEA-Review-2015-024.pdf:80.64MB

Japan Atomic Energy Agency (JAEA) at Tono Geoscience Center (TGC) is pursuing a geoscientific research and development project namely the Mizunami Underground Research Laboratory (MIU) Project in crystalline rock environment in order to construct scientific and technical basis for geological disposal of High-level Radioactive Waste (HLW). The MIU Project has three overlapping phases: Surface-based Investigation phase (Phase I), Construction phase (Phase II), and Operation phase (Phase III). The MIU Project has been ongoing the Phase III, as the Phase II was concluded for a moment with the completion of the excavation of horizontal tunnels at GL-500m level in February 2014. This report presents the results of the investigations, construction and collaboration studies in fiscal year 2014.

Hydrothermal chloritization processes from biotite in the Toki granite, Central Japan; Temporal variations of the compositions of hydrothermal fluids associated with chloritization

Yuguchi, Takashi; Sasao, Eiji; Ishibashi, Masayuki; Nishiyama, Tadao*

American Mineralogist, 100(5-6), p.1134 - 1152, 2015/05

https://doi.org/10.2138/am-2015-5126

This paper describes the biotite chloritization process with a focus on mass transfer in the Toki granitic pluton, Central Japan, and also depicts the temporal variations in chemical characteristics of hydrothermal fluid associated with chloritization during the sub-solidus cooling of the pluton. Singular value decomposition (SVD) analysis results in chloritization reaction equations for eight mineral assemblages, leading to the quantitative assessment of mass transfer between the reactant and product minerals, and inflow and outflow of components through the hydrothermal fluid. The matrices for SVD analysis consist of arbitrary combinations of molar volume and closure component in the reactant and product minerals. The eight reactions represent the temporal variations of chemical characteristics of the hydrothermal fluid associated with chloritization: the progress of chloritization results in gradual increase of silicon, potassium and chlorine and gradual decrease of calcium and sodium in the hydrothermal fluid with temperature decrease. The biotite chloritization involves two essential formation processes: Formation Process 1, small volume decrease from biotite to chlorite and large inflow of metallic ions from the hydrothermal fluid, and Formation Process 2, large volume decrease and large outflow of metallic ions into hydrothermal fluid. Chlorite produced during Formation Process 1 dominates over that of Formation Process 2, resulting in the gradual decrease of metallic components in the hydrothermal fluid with chloritization progress. The combination of continuous reactions based on compositional variations in chlorite together with corresponding continuous Al variations gives an indication of the temporal variations in rates of decreasing and increasing concentration of chemical components in the hydrothermal fluid associated with chloritization.

Characterization of water conducting fracture and their long-term behavior in deep crystalline rock; A Case study of the Toki granite

Ishibashi, Masayuki; Ando, Tomomi*; Sasao, Eiji; Yuguchi, Takashi; Nishimoto, Shoji*; Yoshida, Hidekazu*

Oyo Chishitsu, 55(4), p.156 - 165, 2014/10

https://doi.org/10.5110/jjseg.55.156

Understanding of long-term history of water-conducting features such as flow-path fractures is key issue to evaluate deep geological environment for geological disposal of high-level radioactive waste (HLW). Thus, we conducted study on the geological features and the long-term behavior of flow-path fractures based on the data obtained at -300m levels in the Mizunami Underground research laboratory (MIU), central Japan. Total 1670 fractures were mapped in underground gallery at the -300m levels. Flow-path fractures occupy about 11% of all fractures. The flow-path fractures are divided into grout filling fractures and low inflow-rate fractures. All of the grout filling fractures is filled with calcite as fracture filling minerals without conspicuous host rock alteration around fractures. The low inflow-rate fractures possessed similar geological character with the sealed fractures which are not acted as flow-path. The geological character of fracture filling and host tock alteration around fractures indicates the history of the formation at the time of intrusion and emplacement of host granite (Stage I), then filling at hydrothermal event (Stage II), and finally opening and elongation during exhumation stage (Stage III). In conclusion, the present flow-path fractures were formed by opening and/or elongation of pre-existed fractures, which were filled at the hydrothermal event, at the time of exhumation.

Mizunami Underground Research Laboratory Project, Annual report for fiscal year 2011

Kunimaru, Takanori; Mikake, Shinichiro; Nishio, Kazuhisa; Tsuruta, Tadahiko; Matsuoka, Toshiyuki; Ishibashi, Masayuki; Sasao, Eiji; Hikima, Ryoichi; Tanno, Takeo; Sanada, Hiroyuki; et al.

JAEA-Review 2013-018, 169 Pages, 2013/09

JAEA-Review-2013-018.pdf:15.71MB

Japan Atomic Energy Agency (JAEA) at Tono Geoscience Center (TGC) is pursuing a geoscientific research and development project namely the Mizunami Underground Research Laboratory (MIU) Project in crystalline rock environment in order to construct scientific and technological basis for geological disposal of High-level Radioactive Waste (HLW). The MIU Project has three overlapping phases: Surface-based Investigation phase (Phase I), Construction phase (Phase II), and Operation phase (Phase III). The MIU Project has been ongoing the Phase II and the Phase III in 2011 fiscal year. This report shows the results of the investigation, construction and collaboration studies in fiscal year 2011, as a part of the Phase II and Phase III based on the MIU Master Plan updated in 2010.

Investigation for grout-filling fracture collected from -300m stage of the Mizunami Underground Research Laboratory Construction Site

Yuguchi, Takashi; Ishibashi, Masayuki; Morikawa, Keita; Kunimaru, Takanori

JAEA-Data/Code 2013-004, 38 Pages, 2013/06

JAEA-Data-Code-2013-004.pdf:15.49MB

Tono Geoscientific Research Unit of Japan Atomic Energy Agency (JAEA) is carrying out the Underground Research Laboratory Project, which is a scientific study revealing the deep geological environment as a basis of research and development for geological disposal of high level radioactive wastes. Nowadays, the project is under the Phase II and Phase III. In the 2011 fiscal year, rock specimens accompanied with grout-filling fracture were collected from -300m Access / Research Gallery of the Mizunami Underground Research Laboratory Construction Site, which were processed into thin sections, and then observed through polarizing microscopy. The grout-filling fracture can be identified as groundwater flow path and thus mass transfer pathway. Investigation methodology and petrological / mineralogical data are basic information for the study of mass transfer in Phase III. This paper presents sampling procedure of rock specimen accompanied with grout-filling fracture and compiles the results of these petrographical observations and analyses.