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Complete $$^{40}$$Ar resetting in an ultracataclasite by reactivation of a fossil seismogenic fault along the subducting plate interface in the Mugi M$'e$lange of the Shimanto accretionary complex, southwest Japan

Tonai, Satoshi*; Ito, Shun*; Hashimoto, Yoshitaka*; Tamura, Hajimu; Tomioka, Naotaka*

We used the K-Ar ages of clay-sized mineral grains to investigate the timing of activity on the fossil seismogenic Minami-Awa Fault. The K-Ar ages from matrix shale of the m$'e$lange range from 85 to 48 Ma and decrease with decreasing amount of detrital mica. In contrast, the K-Ar ages of an ultracataclasite within the fault core are significantly younger, ranging from 29 to 23 Ma, and are unrelated to grain size. This indicates that $$^{40}$$Ar diffused completely from the ultracataclasite between 29 and 23 Ma. The diffusion of $$^{40}$$Ar in the ultracataclasite was probably caused by frictional heating or high-temperature fluid migration that occurred when the fault was reactivated. The results indicate that seismogenic faults that separate tectonic m$'e$lange from coherent strata in accretionary complex may slip, not only during accretion, but also long after accretion.



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Category:Geosciences, Multidisciplinary



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