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Ashio Rhyolitic Welded Tuff

Invalid synonym: Ashio Rhyolite

• Type locality: Mount Bizentateyama, Ashio town, Nikko city, Tochigi prefecture
• Volcanic rocks
• Caldera-fill pyroclastic flow deposit
• Miocene (10.3 Ma, U-Pb; 11.3 Ma, K-Ar)

• Lithofacies: Rhyolitic welded tuff
• Lithofacies (Minor): Rhyolite dykes, Tuff breccia

• Thickness: A few dozen m
• Distribution: Funnel shape
• Distribution (Major axis): ca. 4 km
• Distribution (Minor axis): ca. 3 km
• Upper limit: Unconformity (Kesamaru volcano, Funaishi Formation)

• Distribution: Mount Bizentateyama - Matsuki - Ginzandaira, Ashio town, Nikko city, Gunma pref.

• Kawata and Ozawa (1955) Ashio, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 57p. (in Japanese with English abstract 7p.)
• Kawata (1955) Nantaizan, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 43p. (in Japanese with English abstract 7p.)