珠江口盆地构造变形特征与白云凹陷构造‒沉积正演模拟研究

The Tectonic Deformation Characteristics of the Pearl River Mouth Basin and Tectonic-sedimentary Forward Modeling of the Baiyun Sag

珠江口盆地构造演化与南海扩张运动之间的关系一直是众多研究者关注的重点,盆地内构造变形信息对南海多期次的扩张运动具有十分重要的指示作用。为研究珠江口盆地构造变形特征与白云凹陷构造演化,本文对横跨珠江口盆地的三条区域地震反射剖面及过白云凹陷沉积中心的地震反射剖面进行精细的构造解析,同时对白云凹陷主控正断层系统开展正演模拟研究。结果表明,过珠江口盆地东部、中部和西部的三条区域地震反射剖面都反映“三隆夹两坳”的结构特征;剖面对比发现盆地中部吸收的累计构造变形量最大,其中白云凹陷最为突出。对白云凹陷内的控凹正断层系统展开的2D-Move几何学正演模拟研究结果表明,该凹陷主要受控于三条北倾的铲形正断层,活动时间集中于T80~T70(约38~32 Ma)。结合白云凹陷反映的强烈活动时间和沉积分布特征,我们认为白云凹陷的形成可能与南海北部早期伸展作用相关,期间可能叠加了西北次海盆的扩张作用;西北次海盆扩张作用结束后,整个珠江口盆地构造演化都受到了东部次海盆扩张作用的影响。

The relationship between the tectonic evolution of the Pearl River Mouth Basin and the spreading movement of the South China Sea has always been an hot issue,the deformation information of the basin is very important for understanding the multiple spreading movements of the South China Sea.In order to study the overall structural deformation characteristics of the Pearl River Mouth Basin and the tectonic evolution of the Baiyun Sag,we reinterpret three regional seismic profiles across the Pearl River Mouth Basin and one across the center of the Baiyun Sag.We also carry out forward modeling on the main normal fault system of the Baiyun Sag.The three seismic sections all reflect the structural characteristics of‘three uplifts and two depressions’.It is also found that the cumulative amount of tectonic deformation is the largest in the central part of the basin,of which the Baiyun Sag is the most prominent.Based on the tectonic-sedimentary deformation characteristics reflected by the seismic section across the Baiyun Sag,we use a 2-D Move forward modeling to study the depression-controlled normal fault system based on fault geometry.The results reveal that the Baiyun Sag is controlled by three main faults,and the active time of the main faults is between the T80 and T70 reflector interfaces(ca.38-32 Ma).The intense activity time and the sedimentary distribution characteristics in the Baiyun Sag indicate that its formation may be related to the initial rifting of the northern South China Sea and superimposed by the spreading of the northwest sub-basin.After the spreading of the northwest sub-basin,the whole Pearl River Mouth Basin was mainly affected by the spreading of the eastern sub-basin.