日本地球惑星科学連合2018年大会

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[JJ] ポスター発表

セッション記号 M (領域外・複数領域) » M-GI 地球科学一般・情報地球科学

[M-GI25] 山岳地域の自然環境変動

2018年5月22日(火) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:鈴木 啓助(信州大学理学部)、苅谷 愛彦(専修大学文学部環境地理学科)、奈良間 千之(新潟大学理学部理学科、共同)、佐々木 明彦(国士舘大学文学部史学地理学科 地理・環境コース)

[MGI25-P03] Sub-Quaternary exhumation rate changes in the Hida range of the Japanese Alps

*Georgina E King1Shigeru Sueoka2Sumiko Tsukamoto3Frédéric Herman4Floriane Ahadi5Cécile Gautheron5Guillaume Delpech5Takahiro Tagami6 (1.Institute of Geological Sciences, University of Bern、2.Japan Atomic Energy Agency, Japan、3.Leibniz Institute for Applied Geophysics, Hannover, Germany、4.Institute of Earth Surface Dynamics, Université de Lausanne, Switzerland、5.UMR Interactions et Dynamique des Environnements de Surface, Université de Paris, Sud, France、6.Department of Geology and Mineralogy, Kyoto University, Japan)

キーワード:Quaternary, Glaciation, Thermochronometry, Exhumation, Luminescence, ESR

The Hida range is one of the largest and highest mountain ranges in Japan. Whilst its exact uplift history remains debated, previous thermochronometric studies imply multiple uplift phases (cf. Sueoka et al., 2016), including within the past 1 Ma when Quaternary climate oscillated between ice-house and green-house conditions. Thermochronometry enables exhumation rates to be determined from the measurement of rates of rock cooling, providing insights into the processes of landscape evolution. A number of higher-temperature thermochronometry ages for the Hida range have been reported previously (e.g. Ito et al., 2013) indicating that the Hida range is undergoing rapid exhumation. We applied two ultra-low temperature thermochronometric methods based on the trapped-charge dating methods of Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) dating to a suite of 19 bedrock samples collected from the Hida range. These techniques are sensitive to temperatures of as low as ~25 oC, enabling late-Quaternary exhumation histories to be constrained potentially allowing variations in erosion rates to be correlated with Quaternary climatic cycles. In contrast to OSL which can only be applied over timescales of up to ~400 ka, ESR may be applicable over the whole Quaternary period, significantly extending the applicability of trapped-charge dating based thermochronometric methods.

The ESR and OSL data yield similar cooling histories indicating rapid erosion of the Hida range over the past 100 ka. Inverting the data for exhumation rates, assuming a geothermal gradient of 60 oC/km reveals a reduction in rates from ~10 mm a-1 throughout MIS4, during which the most intense glaciation of the Japanese Alps occurred (Iwata, 2003), to ~1-3 mm a-1 over the past 20 ka. Our preliminary data indicate that exhumation rates within the Hida range were higher under a cooler and wetter climate and that glacial erosion processes may have been significant at sub-Quaternary timescales.

References

Ito, H., Yamada, R., Tamura, A., Arai, S., Horie, K., Hokada T., 2013. Earth’s youngest exposed granite and its tectonic implications: the 10-0.8 Ma Kurobegawa Granite. Scientific Reports 3: 1306.

Iwata, S., 2003. Geomorphological environments of the Japanese Alps since the Last Glacial: Gravitational and Glacial Landforms and Alpine Permafrost. The Quaternary Research 42(3), 181-193. (in Japanese with English abstract).

Sueoka S., Tsutsumi H., Tagami T., 2016. New approach to resolve the amount of Quaternary uplift and associated denudation of the mountain ranges in the Japanese Islands. Geoscience Frontiers 7(2), 197-210.