[S-GL21] Geochronology and Isotope Geology

[SGL21-P06] Deformation history of the Atera fault, central Japan

*Horst Zwingmann¹, Masakazu Niwa², Andrew Todd³ (1.Kyoto University, KUEPS, Japan, 2.Tono Geoscience Center, JAEA, Japan, 3.CSIRO Energy, Kensington, WA, Australia)

Keywords:Atera fault, K-Ar dating, authigenic illite

Active inland faults are widespread in Japan and investigations are important for earthquake forecasting and seismic hazard assessments (Toda, 2016). The Atera fault is one of several major, left-lateral, strike–slip active faults in central Japan and extends for >50 km inGifu Prefecture. Outcrops are sparse, and we describe authigenic illite fault gouge age dating results from a unique outcrop with fault breccia, clay-rich fault gouge, and cataclasite, recording several stages of deformation within its fault zone architecture (Niwa et al., 2009, 2015). This study investigates the timing of fault formation by K-Ar dating of authigenic illite (<0.1, <2 and 2-6 micron fractions) separated from 3 fresh, non- weathered samples from the outcrop at Kawaue, Nakatsugawa city. Prior to age dating, extensive mineral characterization was carried out comprising petrography (TS, SEM, TEM) and XRD clay analyses (e.g. Zwingmann et al., 2010). An undeformed host rock yields an age of ~ 55 Ma (Paleogene-Eocene) and the Atera fault gouges clay ages range from 40 to 60 Ma (Paleogene-Eocene to Paleocene) and will be discussed within the geochronological and thermochronological background of the study area.

This study was funded by 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 (JPJ007597) (Fiscal Years 2018-2022)”.

References
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Toda, S., 2016. Crustal earthquakes. - In: Moreno, T., Wallis, S., Kojima, T. and Gibbson, W. (eds) 2016. The Geology of Japan. Geological Society, London, 371-408.
Zwingmann et al., 2010. Geology, v. 38, no 6, 487-490; doi10.1130/G30785.1