諏訪湖北方および南方の中央構造線 : 特に中新世以後の活動について
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概要
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The Median Tectonic Line, the geologic boundary between the Inner and Outer Zone of Southwest Japan, crosses the Itoigawa-Shizuoka Tectonic Line in the Suwa region, Nagano Prefecture, and it extends into the Fossa Magna region. There are many reports on the movements of the Median Tectonic Line during the Quaternary in Southwest Japan. In the Fossa Magna region, however, even the location of the Tectonic Line remained uncertain. The writer clarified the exact location of the Tectonic Line around Lake Suwa, and obtained the following informations concerning its movements from Miocene to Pleistocene. 1. The Median Tectonic Line in the northern part of the Akaishi Mountains runs through west of the Tsuetsuki Pass, with a N10°E-N20°E direction, to Takabe at the southern part of the Suwa Basin. The faulting movement occurred probably during the Quaternary as an expression of the block movements in the Suwa region. 2. The Yokokawagawa Fault along the River Yokokawato the north of Lake Suwa has a strike of N20°E, and is found in the Fossa Magna region. It is the geological boundary between the Neogene formations to the west and the crystalline schists of the basement to the east. It seems that this fault is a surface representation of the movement of the Median Tectonic Line. It would be middle to late Miocene in age, and it was accompanied with igneous intrusion and mineralization. As a result of this large-scale faulting the crystalline schists of the basement were brought to the earth's surface in the central part of the Shinshu green tuff region. This is a phase of the Bessho phase earth movement. 3. The Median Tectonic Line is displaced laterally 11-12 km along the Itoigawa-Shizuoka Tectonic Line.
- 日本地質学会の論文
- 1976-12-30
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- 諏訪湖北方および南方の中央構造線 : 特に中新世以後の活動について