渤海海域郯庐断裂带新生代活动方式与演化规律——以青东凹陷为例

青东凹陷东边界为郯庐断裂带在渤海海域内西支断裂所在,平面上由4条北北东向断裂呈左阶雁列式排列,剖面上以上盘下降为主,局部具有张扭性和压扭性花状构造现象。青东凹陷东界上的郯庐断裂新生代经历了古近纪右行平移正断层活动、古近纪末盆地挤压反转中的逆右行平移、新近纪的弱拉张活动和第四纪以来的逆右行平移4个演化阶段。古近纪断陷期,先存的郯庐断裂带由于具有较低的强度,在南北向伸展应力场作用下复活并表现为具有右行平移分量的斜向拉张活动,在浅部新生4条左阶雁列式断层,并与盆地内北西向基底断裂系统和东西向新生正断层共同控制了古近系的沉积格局。古近纪末发生了盆地反转,结束了断陷盆地发育阶段,在北东东-南西西向区域挤压应力作用下郯庐断裂表现为逆右行平移活动。新近纪坳陷阶段,盆地内构造活动较弱,主要受控于岩石圈热沉降作用,但郯庐断裂仍具有较弱的伸展活动。第四纪以来,郯庐断裂再次转变为逆右行平移活动。

Cenozoic activity methods and evolution of the Tan-Lu fault zone in Bohai Bay:Evidence from the Qingdong Sag

Western branch of the Tan-Lu fault zone lies along the eastern boundary of the Qingdong Sag in Bohai Bay.The Tan-Lu faults consists of 4 left-step,en-echelon faults.They show normal faulting on cross-sections and local flower structures related to transtension or transpression.The Tan-Lu faults along the Qingdong Sag evolved from dextral normal faulting of Paleogene,reverse dextral faulting at the end of Paleogene,weak normal faulting of Neogene to reverse dextral faulting of Quaternary.The pre-existing Tan-Lu faults reacted as dextral normal faults under oblique N-S extension due to their lower strengths during Paleogene rifting,leading to formation of the 4 left-step,en-echelon faults at shallow levels.Paleogene deposition patterns in the sag were controlled by the Tan-Lu faults,NW-striking basement faults and E-W new normal faults.The Basin inversion at the end of Paleogene terminated development of the rifted basin and caused reverse dextral faulting of the Tan-Lu faults due to regional ENE-WSW compression.Weak faulting was associated with the Neogene depression related to lithospheric thermal subsidence,and the Tan-Lu faults show weak normal faulting.The Tan-Lu faults switched into reverse dextral faulting since the beginning of Quaternary.