欧亚东边缘的双向板块汇聚及其对大陆的影响

自3 Ma至现今,在欧亚东缘太平洋、菲律宾海板块以较大速率朝NWW方向运动,并沿海沟向欧亚大陆俯冲;同时欧亚板块以较小速率朝SEE方向移动,构成双方向的板块汇聚格局.沿日本岛弧东侧,海洋板片以较小的倾角插入欧亚大陆下面,在浅部产生的挤压变形扩展到日本海东边缘.琉球岛弧的中、北部,菲律宾海俯冲板片的倾角较大,其西南段由NE向转变为EW向,正经历活动的海沟后退与弧后扩张.台湾是3种板块汇聚的交点:欧亚沿马尼拉海沟向东俯冲,吕宋弧与台湾碰撞,使台湾岛陆壳东西向缩短与隆升,形成年轻的造山带,菲律宾海板块沿琉球海沟的西南段向北俯冲到欧亚下面.位于南海与菲律宾海之间的菲律宾群岛是宽的变形过渡带,两侧被欧亚向东、菲律宾海向西俯冲夹击,中间是大型左旋走滑断层.总体上,现今时期的太平洋、菲律宾海板块的西向俯冲运动所产生的变形主要分布在俯冲板片内部及岛弧,未扩散到弧后地区,可能这种俯冲运动产生的水平应力较小,不能阻挡欧亚大陆的向东移动,对大陆内部的现今构造没有明显的影响.

Two-directional plate convergence along the east margin of Eurasia and its influence on the continent

Since 3 Ma,the Pacific and Philippine Sea plates moved towards NWW at a greater rate along east margin of Eurasia and subduct at the oceanic trench.At the same time,the Eurasian plate moves to SEE at a smaller rate,thus forming a two-direction plate convergence pattern.The oceanic slab plunges beneath the Eurasian continent at a small dip on the east side of Japan island-arc,causing compressive deformation in the shallow subsurface that extends to east edge of the Japan Sea.In the central and northern Ryukyu arc,the subducting Philippine Sea slabs dip west at a relatively big angle,while the southwest section of this arc is experiencing active trench retreat and back-arc spread.Taiwan is a locus where three kinds of plate convergence coexist: the Eurasian subducts east along the Manila trench,the Luzon arc collides with Taiwan producing east-west compression and young mountain building of the Taiwan crust,and the Philippine plate underthrusts toward north below the Eurasian along the southwest Ryukyu trench.The Philippine islands is a broad transitional zone of deformation where the Eurasian plate subducts to east and the Philippine Sea plate underthrusts to west on either side of the islands.Overall,the deformation generated by the Pacific and Philippine Sea plate motions seems to concentrate in the slab interiors and island arcs proper,not extending to the back-arc regions and farther west to the Eurasian continent.Probably the horizontal stress component produced by these subducting plates is relatively small so that it cannot stop the slow eastward motion of the Eurasian continent and poses no considerable influence on the present-day intracontinental tectonics of Eurasia.