青东凹陷复合型花状构造成因分析

青东凹陷内大型北西-北西西基底断层上发育一种结构特殊的花状构造——复合型花状构造,在凹陷内表现为构造高带,对油气成藏具有重要的控制作用。在三维地震剖面的解释和分析基础上,结合平面构造反射层资料的综合分析,发现其中的断层在平面上以右阶雁列式或平行式组合排列,剖面上基底主断层向上撒开并与多条次级断层组合成似花状构造。组成这些似花状构造的断层均为正断层,但其中的地层却表现为上拱的背形。根据断裂发育特点及区域构造应力演化特征对其进行成因分析,认为其形成是由于北西-北西西向基底断层在盆地南北向拉伸下的张扭性(斜向拉张)活动与古近纪末反转期压扭性活动叠加的结果。其形成过程经历了古近纪伸展期似负花状构造形成阶段和古近纪末反转期背形构造形成阶段。

Analysis on the Origin of the Composite Flower Structures in the Qingdong Sag

There is a special kind of flower structures in the Qingdong sag,termed as composite flower structure,which developed upon the large NW-NWW trending basement faults.The structures are shown as structural uplifting belts,and play an important role in controlling hydrocarbon enrichment.Based on analysis of 3D seismic profiles and surface structures,it is found that faults in the belts present an en-echelon or parallel arrangement horizontally,and these special flower-like structures are composed of a major basement fault that radiates upward,and many subsidiary faults on vertical profiles.Faults comprising the flower-like structures are normal faults,but strata in the structural belts appear as arched antiforms.According to the fault characteristics and stress field evolution in this area,it is proposed that the composite flower-like structures are caused by structural superimposition of earlier transtension faulting(oblique extension)along the NW to NWW-striking basement faults under a N-S extension and later transpression faulting due to the inversion at the end of Paleogene.Evolution of the composite flower structures experienced formation of the negative flower-like structure during the Paleogene extension and antiform structure overprinting during the inversion period at the end of Paleogene.