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[R8P-15] Constraint on the low-temperature mylonite and phyllonite formations along the Median Tectonic Line in the Oshika district, Nagano
Keywords:Kashio mylonite, Ryoke metamorphic rock, Sanbagawa metamorphic rock, U-Pb ages
The U-Pb ages of zircons in the Kashio mylonite and Sanbagawa metamorphic rocks were analysed by LA-ICPMS. The prominent age spectra of the ultramylonite showed 69.0 ± 0.6 Ma (n=10). On the other hand, two age data (YSG; 70.7 ± 1.5 Ma, YC1σ; 71.2 ± 0.91 Ma) were obtained from Sanbagawa metamorphic rocks. Based on our data, two stages of mylonitization were estimated: ca. 67 Ma and 65Ma. The later stage of mylonitization is well consistent with the phyllonite formation and Sanbagawa metamorphism in the Oshika district. Thus, Ryoke and Sanbagawa belts were amalgamated along the MTL at ca. 65 Ma.