美濃帯のメランジュ(地質構造と変形過程)(ジュラ紀付加体の起源と形成過程)  [in Japanese] Melanges of the Mino Terrane(Geologic structure and tectonic process)(Origin and evolution of Jurassic accretionary complexes in Japan)  [in Japanese]

美濃帯のメランジュは, 砂岩・泥岩・礫岩・珪質泥岩・チャート・石灰岩・玄武岩などからなる.放散虫化石により復元された原岩層序は"海洋プレート層序"と呼ばれ, 海洋プレートが生まれ海溝で沈み込むまでの歴史を記録している.この海洋プレート層序がどのような過程で破断・変形・混合したのかを検討するために, 地質図規模・露頭規模・薄片規模でメランジュの性質を検討した.美濃帯のメランジュでは, 海洋プレート層序のうち砥石型珪質粘土岩と優黒色有機質泥岩の層準を中心に破断・変形・混合が進行し, 周囲の砂岩やチャートなどを礫・岩塊として取り込んでいった.長さ1 kmを超えるスラブは, 海洋プレート層序のうち破断・変形・混合を免れた部分として理解することができる.このように, 美濃帯のメランジュは, 付加体の形成過程に伴って, 海洋プレート層序が次第に破断・変形・混合され, 複雑な構造を有するようになった.

The Mino terrane is one of the best investigated melange terranes in the world. The terrane is composed mainly of various types of melanges, broken formations, turbidites, and tectonic slabs. The components of the melanges and other disrupted units had an original sequence mainly of basalt, limestone, siliceous claystone, chert, siliceous mudstone, and turbidite in ascending order. The terrane was formed by the subduction of an oceanic plate during Early Jurassic to earliest Cretaceous time along the eastern margin of the Asian continent. The reconstructed succession mentioned above is called "oceanic plate stratigraphy" (OPS) which indicates the history of the subduction and accretion of ancient oceanic plates.The melanges of the Mino terrane were investigated by means of combining geologic mapping, detailed observation on an outcrop scale, radiolarian biostatratigarphy and structural analysis. The melanges are assemblages of variously deformed and disrupted slabs, blocks and clasts whose protoliths were derived from the OPS. A decollement, or detachment fault was developed in a layer of siliceous claystone which is sometimes highly deformed parts in the melanges. The basalt and limestone blocks and slabs are included in the strongly sheared black shale originated from the lower part of the siliceous claystone. The OPS is progressively disrupted mainly by tectonic processes, although sedimentary and diapric processes possibly contributed to the melange formation in an earlier stage.