红河断裂带的新生代变形机制及莺歌海盆地的实验证据

DEFORMATION MECHANISM OF RED RIVER FAULT ZONE DURING CENOZOIC AND EXPERIMENTAL EVIDENCES RELATED TO YINGGEHAI BASIN FORMATION

红河断裂带是印藏碰撞过程中 ,印支地块被顺时针旋转挤出的走滑变形带。莺歌海盆地发育于红河断裂带海上延伸带上。根据莺歌海盆地和相邻的NE向琼东南盆地在晚中新世前 (5 .5MaB .P .)独立的构造发育和差异的沉降特点 ,认为红河断裂不可能穿越莺琼盆地界限向北东延伸 ,而越东断裂和中建南断裂很可能是红河断裂的延续。莺歌海盆地成盆机制的物理模拟结合红河断裂带陆上的变形特征、年代学证据与青藏高原隆升过程的研究 ,参考莺歌海盆地模拟过程中不同应力场下沉降中心的长轴方向 ,我们推断红河断裂带新生代的演化大致分 4个阶段 :(1 ) 50— 38MaB .P .期间的缓慢平移运动 ;(2 ) 38— 2 5MaB .P .期间的快速左行走滑运动 ;(3) 2 5— 5MaB .P .期间的左行走滑逐渐停止阶段 ;(4) 5MaB .P .后的右行走滑阶段。

The Red River Fault Zone is a strike-slip zone along which Indochina Block was extruded during India-Tibet collision. The Yinggehai basin developed on the seaward elongation of the Red River Fault Zone. Before Late Miocene (5.5Ma B.P.), structures and subsidence developed in the Yinggehai and Qiongdongnan Basins are separate and discrepant, so we conclude that it s impossible for the Red River Fault Zone to extend northeastwards. The analogue modeling of the formation of the Yinggehai Basin proves that the East Vietnam Fault may be the extension of the Red River Fault Zone. Combining the inland movement and chronology of the Red River Fault Zone with the uplift of Tibet, and referring to the orientation of depocenter axis in the Yinggehai basin, we conclude that the Cenozoic motion of the Red River Fault Zone can be divided into four stages: (1) from about 50Ma to 38Ma B.P., the Red River Fault Zone slipped sinistral slowly;(2)from 38Ma to about 25Ma B.P., rapid sinistral silp of the Red River Fault Zone;(3) from 25Ma to 5Ma B.P., sinistral slip slowed down;(4) dextral slip of the Red River Fault Zone after 5Ma B.P.