[S-CG47] Evolution and movement of the crustal surface and application of geo- and thermochronology

[SCG47-P04] Exhumation history of the Kurobe area, Hida Range, based on formation depths and ages of the Pliocene-Quaternary plutons

*Shigeru Sueoka¹, Tetsuo Kawakami², Kota Suzuki², Ayu Yamazaki², Saya Kagami¹, Mitsuhiro Nagata¹, Tatsunori Yokoyama¹, Takahiro Tagami² (1.Japan Atomic Energy Agency, 2.Kyoto University)

Keywords:Kurobegawa granite, Quaternary pluton, Al-in-Hbl geobarometry, zircon U-Pb dating, exhumation, Hida Range

Plutons are formed at depths of 100-101 km, generally requiring >107 years to be exhumed and finally exposed to the Earth’s surface. Nonetheless, plutons younger than ~5 Ma have been reported in several areas, mainly along plate boundaries (Harayama, 1992). In the Kurobe region of the Hida Range, central Japan, granitoids intruded intermittently at 10-0.8 Ma (Ito et al., 2013, 2017). However, the exhumation rate and mechanism of the young plutons are not well understood partly because thermochronology is difficult to apply to a region having such a complex thermal history and structure. In fact, exhumation history of the Kurobe region is constrained poorly in spite of a series of thermochronometric data including young cooling ages of a few Ma and <1 Ma (e.g., Ito and Tanaka, 1999; Yamada & Harayama, 1999; Yamada, 1999; Spencer et al., 2019). We utilize geobarometers to reveal exhumation history in the Kurobe region, by determining formation depths of the plutons by Al-in-Hbl geobarometer (Hollister et al., 1987; Schmidt, 1992; Takahashi, 1993; Mutch et al., 2016) and the formation ages by zircon U-Pb dating. This presentation will provide the preliminary results and interpretations as follows: 1) formation depths of ~5 Ma and ~0.8 Ma plutons were estimated to be ~6-9 km, which indicates increase of the exhumation rate after ~0.8 Ma, 2) mean exhumation rate since ~0.8 Ma was computed at 8-10 mm/yr in the Baba-dani area, 3) the formation depths are uniform in E-W direction, disagreeing with the eastward tilting model (Harayama et al., 2003, 2010; Harayama, 2015).

Acknowledgements:
This study was funded by the Ministry of Economy, Trade and Industry (METI), Japan as part of its R&D supporting program titled “Establishment of Advanced Technology for Evaluating the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste (Fiscal Years 2018 and 2020)”.