琉球海沟构造地貌

On the Structural Landforms of the Ryukyu Trench

琉球海沟位于西北太平洋，与琉球岛弧和冲绳海槽同属于一个沟弧盆体系。它紧贴琉球岛弧东侧，与琉球岛弧平行延伸，长约１３５０ｋｍ，水深５０００～６０００ｍ，最大水深７８８１ｍ。其地貌明显地受构造因素控制。中新世以来，西北菲律宾海板块插入亚洲板块之下，琉球岛弧隆起，形成不对称的“Ｖ”型深海沟。海沟西坡（岛坡）陡，并受众多的横断裂切割，坡上有众多的北西—南东向的海底沟谷，还有北东—南西向的陡崖。坡间水深１５００～４０００ｍ之间为宽阔的由玄武岩质火山岩构成的阶地面，其上有浊流沉积。岛坡经多个陡崖，急倾至海沟底。东坡（洋坡）缓，是西北菲律宾海板块向琉球岛弧下插的一边，与大洋盆地相连。海沟的轴部是菲律宾海板块和欧亚板块俯冲会聚边界。由于断裂的割切，致使海沟底地貌复杂化。只在琉球海沟的中段，海沟深度超过６０００～７０００ｍ处深海沟构造地貌特征最为典型。

The Ryukyu Trench, which belongs to the same TABA system as the Ryukyu Island Arc and the Okinawa Trough, is located in the northwest part of the Pacific Ocean. It is close to the east side of the Ryukyu Islands, stretches parallelly to the Ryukyu Island Arc. It is about 1350km long and about 5000~6000m deep, the greatest depth being 7881m. The Ryukyu Trench landforms are obviously controlled by the structural factors. At the end of the Miocene, the northwest Philippine Plate inserted under the Asia Plate, the Ryukyu Island Arc rose, the Ryukyu Trench became an asymmetrical Vtyped deep trench. The west slope of the Trench is steep, cutting by many cross faults. At the slope, there are many submarine valleys in the NWSE direction, and also there are steepcliffs in the NESW direction. The area where the water depth is between 1500m and 4000m is a broader terrace area composed of basaltic volcanic rock, and there are turbidity sediments on it. The islandslope inclines to the trench bottom across many steepcliffs. The east slope is slow, and is the inserting side from the northwest Philippine Plate into the Ryukyu Island Arc, connecting with the ocean basin. The axis of the Ryukyu Trench is the convergent margin of the Philippine Plate and the Eurasia Plate. The submarine geomorphology is complex due to the crossfaults cutting. Only in the middle part of the Ryukyu Trench, where the depth is over 6000~7000m, exist the most typical geomorphological characters of a deep trench.