方正断陷新生代结构构造及其演化分析

Cenozoic Structural Characteristics and Evolution in the Fangzheng Fault Depression, Northeast China

以方正断陷二维、三维地震资料和钻井资料为基础,追踪和闭合了盆内重要的新生代构造层序界面。富锦组底界面为区域性裂后不整合界面,将盆地的演化阶段划分为裂陷期和裂后期。在裂陷期的充填序列中,宝泉岭组底界面为盆内易于识别的区域性角度不整合界面,该界面将盆地的裂陷期进一步划分为裂陷Ⅰ幕和裂陷Ⅱ幕。本文通过对盆地结构构造及不同时期厚度特征的分析,重建了盆地的形成演化过程。研究结果表明,裂陷Ⅰ幕构造活动受NW-SE向的正向伸展应力控制,发育的E1w-E2d地层充填在简单地堑盆地中;裂陷Ⅱ幕的E3b时期以近SN向斜向伸展作用下形成的断阶式地堑结构为特征,盆地沉积-沉降中心位于盆内伊汉通断裂下降盘,且具有从北向南迁移的趋势。裂后期N1f时期以热沉降为主,并伴随有右旋走滑作用。另外,盆地的形成演化经历了三期反转改造过程,分别对应始新世晚期、渐新世晚期和上新世晚期。结合周缘板块的运动学重组事件,认为太平洋板块西侧俯冲方式的变化和印度-欧亚板块碰撞的远程效应联合控制了方正断陷新生代的形成演化过程。

Based on the 2D and 3D seismic data and drilling data in the Fangzheng Fault Depression, we tracked and outlined the important Cenozoic tectonic sequence interfaces in the basin. The bottom interface of the Fujin Formation is a regional post-rifting unconformity which divides the basin’s Cenozoic evolution into rifting and post-rifting stage. In the filling sequence of the rifting stage, the bottom interface of the Baoquanling Formation is also an easily identified regional angle unconformity dividing the rifting stage into two phases. Through analyzing the structural characteristics and the strata thickness of different stages in the Fangzheng Fault Depression, this paper reconstructed the formation and evolution of the basin. The results show that the study area was controlled by the NW-SE extending stress field in the rifting EpisodeⅠwith E1w-E2d strata filling in a simple graben basin;however, the stress field turned to nearly SN obliquely extending stress in the rifting Episode Ⅱ during E3b characterized by fault-stepped graben. Meanwhile, the sedimentary-subsidence center was located in the downthrown side of the Yihantong Fault with the trend of migration from north to south;the post-rifting stage during N1f was dominated by thermal subsidence and accompanied by dextral strike-slip. In addition, the formation and evolution of the basin experienced three contraction inversion processes during Cenozoic, corresponding to the late Eocene, the late Oligocene and the late Pliocene. Finally, combined with the global kinematics reorganization event of plates, we suggest that the subduction of the Pacific plate relative to Eurasian plate and India-Eurasia collision effects jointly controlled the formation and evolution of the Fangzheng Fault Depression during Cenozoic.