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

[SCG47-04] Constraining thermal/denudation histories in the last 0.1 Myr using OSL thermochronometry applied to samples from deep boreholes -A case study in Rokko Mountains-

*Manabu Ogata¹, Georgina E King², Frédéric Herman², Shigeru Sueoka¹, Ryuji Yamada³, Kentaro Omura³ (1.Tono Geoscience Center, Japan Atomic Energy Agency, 2.Institute of Earth Surface Dynamics, University of Lausanne, 3.National Research Institute for Earth Science and Disaster Prevention)

Keywords:optically stimulated luminescence, thermochronology

Optically stimulated luminescence (OSL) thermochronometry is a method for estimating the thermal histories in the ultra-low-temperature domain less than several tens of degree Celcius [1][2][3]. This method enables reconstructing the exhumation histories of a period over which rocks are exhumed by several hundred meters assuming a geothermal field. Application of OSL-thermochronometry is currently limited to regions that have experienced denudation rates higher than 5 mm/yr (assuming a general geothermal gradient in Japan; ~0.03℃/m); luminescence signals saturate before the rocks are exhumed to the surface in slowly-denuding regions. However, constraining the slow cooling histories may be possible if unsaturated samples are obtained from deep boreholes.

We apply OSL-thermochronometry to deep borehole cores drilled at the Rokko Mountains that have experienced moderate denudation rates (0.1-1.0 mm/yr). We used the Kabutoyama core collected by National Research Institute for Earth Science and Disaster Resilience [4][5]. The total length of Kabutoyama core is 1,313 m and we collected the samples at 408, 642, 818 and 1048 m for OSL thermochronometry. In this presentation, we will present the OSL thermochronometry results, and discuss landform development history based on these results and previous studies on uplift and denudation rates.

This study was carried out under a contract with METI (Ministry of Economy, Trade and Industry) as part of its R&D supporting program for advanced research on long-term stability of geological environment.



References:

[1] Herman et al. (2010). Earth and Planetary Science Letters, 297, 183-189.

[2] King et al. (2016). Quaternary Geochronology, 33, 76-87.

[3] Herman and King (2018). Elements, 14, 33-38.

[4] Yamada et al. (2012). Technical Note of the National Research Institute for Earth Science and Disaster Prevention, 371, 27p.

[5] Sueoka et al. (2010). Journal of Geography, 119, 84-101.