南部フォッサマグナの形成 : 堆積物からみた島孤の衝突付加テクトニクス  [in Japanese] Construction of the South Fossa Magna : Collision and accretion tectonics of arcs deduced from the sedimentary sequences  [in Japanese]

南部フォッサマグナは, フィリピン海プレートの運動に伴って北上してきた古伊豆-小笠原弧に属する微小大陸の衝突によって形成された。微小大陸の衝突は, 中期中新世以降4回起こったものと考えられる。第1回目は巨摩地塊の衝突(13-12 Ma)。第2回目は御坂地塊の衝突(12-11 Ma), 第3回目は丹沢地塊の衝突(6 Ma前後), 第4回目は伊豆地塊の衝突(1 Ma前後) である。微小大陸の衝突・付加により, 後背地が上昇し, その前面にあるトラフに礫岩を主体とする粗粒堆積物が供給された。小断層や岩脈から復元された最新期の伊豆地塊の衝突以降の応力場の方向は, NW-SEでフィリピン海プレートの運動方向と調和的である。

The South Fossa Magna was formed by the collision and the accretion of the micro-continents which moved from the south in connection with the movement of the Philippine Sea Plate. The collision of the micro-continents occurred four times after the Middle Miocene: the first, the collision of the Koma massif (13-12 Ma); the second, the collision of the Misaka massif (12-11 Ma); the third, the collision of the Tanzawa massif (ca 6 Ma); and the fourth, the collision of the Izu massif (ca 1 Ma). The rising hinterlands which resulted from the collision and the accletion of the micro-continents, supplied large amounts of coarse sediments which filled the trough in front of these hinterlands. The stress in the Izu massif collision, which is deduced from the micro-faults and the dykes in the Fujigawa and the Ashigara Groups, is NW-SE in the maximum compressive stress direction. This direction is consistent with the movement of the Philippine Sea Plate which is revealed in the geophysical data.