西太平洋弧后地区新生代构造迁移的深部地震证据

Deep Seismic Evidence of Cenozoic Tectonic Migration in the Western Pacific Back-Arc Area

为了研究西太平洋弧后边缘海盆地的深部构造特征,于2015年在东海琉球岛弧弧后地区布设了一条穿过东海陆架盆地、钓鱼岛隆褶带、南冲绳海槽地区和琉球岛弧的主动源广角反射/折射深部地震剖面.利用走时正演和反演的方法得到的二维速度结构模型展现了西太平洋边缘弧后地区莫霍面的深度由东海陆架地区的大于30 km显著抬升至南冲绳海槽轴部的约16 km,地壳高度拉张减薄,并存在一系列显著的不连续下地壳高速体,速度达6.8~7.3 km/s,这是地幔上涌的显著表现.模型从深部结构角度展现了新生代以来西太平洋弧后盆地扩张中心的变迁,证实了西太平洋洋陆过渡带内深部上涌的软流圈在弧后拉张过程中不断地向洋跃迁,形成自西向东的构造迁移,并带动岩石圈进行幕式伸展,认为新生代向洋变新的构造迁移是太平洋俯冲带后撤引起的一系列弧后深-浅部地球动力效应.

To study the deep crust structure in the back-arc area,we present an active source wide-angle reflection/refraction profile in the back-arc area of Ryukyu Island in the East China Sea in 2015,which passed through the East China Sea shelf basin,the Diaoyu island uplift belt,the southern Okinawa Trough and the Ryukyu Island arc.The 2 D velocity structure model obtained by forward modeling and travel tomographic shows that the depth of Moho rises significantly from more than 30 km in the East China Sea shelf to about 16 km in the axis of the Okinawa Trough,and the crustal thickness decreases significantly.A series of discontinuous high-velocity zones with velocity 6.8-7.3 km/s were identified in the lower crust of the back-arc region,which is a remarkable manifestation of mantle upwelling.From the perspective of deep crustal structure,the model clearly shows the tectonic migration from west to east in the back-arc area of the Western Pacific since Cenozoic and confirms that the as thenosphere upwelling in the deep part of the Western Pacific oceanic-continental transition zone transits continuously to the ocean during the back-arc spreading process,forming the tectonic migration from west to east,and driving the episodic extension of the lithosphere.We believe that the Cenozoic tectonic migration to the ocean is a series of back-arc deep-shallow geodynamic effects caused by the retreat of the Pacific subduction zone.