Timing of mylonitization in the Funatsu Shear Zone within Hida Belt of southwest Japan: Implications for correlation with the shear zones around the Ogcheon Belt in the Korean Peninsula

摘要

The Funatsu Shear Zone is an early Mesozoic dextral ductile shear zone located in the Hida Belt of southwest Japan, consisting mainly of granite mylonites. The Jurassic Funatsu granites intrude the Hida metamorphic rocks and the granite mylonites. The SHRIMP U-Pb zircon ages of granite mylonites in the Funatsu Shear Zone around the Tateyama area are 250.2 +/- 2 Ma and 240 +/- 2 Ma. SHRIMP U-Pb zircon age of the Okumayama granodiorite, which is a member of the Funatsu granites and which intrudes the granite mylonite, is 191 +/- 3 Ma. We interpret that the timing of mylonitization in the Funatsu Shear Zone to be after 240 Ma and prior to 191 Ma (Triassic to Early Jurassic), and possibly around 215-211 Ma (Late Triassic), corresponding to the K-Ar ages of hornblende in basic inclusions of the granite mylonite. In the Korean Peninsula, dextral ductile shear movement occurred in the Cheongsan Shear Zone of south central Ogcheon Belt during Middle to Late Triassic time accompanied by the intrusion of Jurassic Daebo granites, which are correlated to the Funatsu granites. The similarities in geology, deformation characteristics, timing of mylonitization and paleogeographic location suggest that the Funatsu Shear Zone can be correlated to the Cheongsan Shear Zone.