莺歌海盆地周边区域构造演化

Regional Tectonic Evolution Around Yinggehai Basin of South China Sea

莺歌海盆地周边新生代区域构造演化综合分析表明 ,该盆地形成和演化构造应力场分四个阶段 :第一阶段 ,古新世末至早渐新世印支地块快速向南东方向挤出 ,同时伴随着地块的顺时针旋转运动。第二阶段 ,晚渐新世至早中新世印支地块向南东挤出运动逐渐减弱 ,华南地块整体仍然相对稳定。莺歌海盆地处于左旋剪切状态。第三阶段 ,中、晚中新世随着印度地块逐渐楔入欧亚板块内部 ,印支半岛的挤出运动进一步减弱。至中中新世末 ,华南地块整体开始挤出。第四阶段 ,上新世—第四纪印支地块相对稳定 ,华南地块挤出运动继续进行 ,两地块间的相对运动呈右旋剪切运动。莺歌海盆地新生代的构造应力场演化受太平洋板块、印度与欧亚板块之间相互作用控制。其中 ,印度与欧亚板块碰撞作用所导致的印支地块与华南地块的相对运动 ,是决定莺歌海盆地新生代构造运动应力场变化的主要因素。

Yinggehai basin is located in the northwest of South China Sea, and formed in the Cenozoic. The Cenozoic sedimentary thickness in the basin is more than 15km, therefore, the structural features related to rifting phase are difficult to reveal by seismic profiling. In order to understand its origin and evolution, we analysed the regional characteristics of the Cenozoic tectonic evolution surrounding Yinggehai basin, and obtained the Cenozoic tectonic stress field of the basin.The formation and tectonic stress field of Yinggehai basin can be divided into four phases. The first phase, from the later Paleocene to the early Oligocene, Indochina block extruded toward southeast fast, with a clockwise rotation movement. Yinggehai basin origined in this stage. The second phase, from the later Oligocene to the early Miocene, Indochina block's southeastward extrusion slowed down gradually. However, South China block was relatively stable and Yinggehai basin was under a left slip shearing condition. The third phase, during the middle and the later Miocene, with the Indochina block intruding into Eurasia plate gradually, Indochina peninsula's extrusion slowed down further. At the end of the middle Miocene, South China block began to extrude integrally. The last phase, from the Pliocene to the Quaternary period, Indochina block was relatively stable, South China block's extrusion continues, the relative movement of these two blocks is right slip shearing. The Cenozoic evolution of tectonic stress field of Yinggehai basin is controlled by the interaction between Pacific plate, India plate and Eurasia plate. Most of all, the relative movement between Indochina and South China block resulted from the India Eurasia collision is the dominate factor of the Cenozoic tectonic stress field controlling the origin and evolution of Yinggehai basin.