渤海湾盆地南堡凹陷断裂系统成因的构造解析

Structural Analysis of Faulting System Origin in the Nanpu Sag,Bohai Bay Basin

本文在对南堡凹陷三维联片地震资料构造解析的基础上,应用先存构造条件下的断层作用模式,结合构造物理模拟实验成果,系统分析了南堡凹陷的断裂系统和构造样式。表明,南堡凹陷是典型的斜向伸展变形样式,其中受铲式和(或)坡坪式边界正断层及先存断裂共同控制的复式"Y"形样式是南堡凹陷基本的构造样式,其次是复式"X"形、"多米诺式"、"阶梯式"和"铲式扇"断块构造样式。平面上划分出4个断裂系统:北堡-老爷庙断裂系统,高柳断裂系统,柏各庄断裂系统和南堡断裂系统,其中高柳断裂系统和南堡断裂系统进一步分别划分为2个和3个子断裂系统;纵向上划分出下部(E2s3构造层)和上部(E2s1-Q地层)两个断裂系统,E2s2是上下两个断裂系统的过渡层,断层不发育。断层的平面组合形式有4种,分别为:平行状、平行交织状、"梳状"和"帚状"。"两期伸展"的变形叠加模式可以合理地解释南堡凹陷新生代的构造变形:E2s3期的构造变形是以中生代形成的先存构造为基础,北西—南东方向伸展作用的结果;E2s1以来的变形是以E2s3期形成的断裂为先存构造,南北向伸展作用的结果;E2s2是应力体制转换的过渡阶段。凹陷边界断层(西南庄断层、柏各庄断层和高柳断层)存在显著的分段性,不同段落断层的走向、性质和活动性均表现出很大的差异,而且在不同构造演化阶段发生显著的变化。凹陷边界断层及凹陷内的南堡断层、和蛤坨断层组成的构造格架对南堡凹陷断裂系统的形成和演化起重要的控制作用,复杂的先存构造是造成断裂系统横向变化的根本原因。

On the basis of structural analysis of 3D seismic data in Nanpu sag,and in combination with faulting model with pre＇existing weaknesses and sand modeling results,the fault system and structural styles in the Nanpu sag were systematically analyzed.The results show that the structural style is typical oblique extension.The complicated ＂ Y＂ shaped style,which is jointly controlled by listric （or ramp-flat） boundary normal faults and pre existing faults,is the basic structural style in the Nanpu sag,followed by complicated ＂X＂ shaped,＂domino＂,＂Ladder＂ and ＂imbricate faulted blocks＂ structural styles.4 fault systems are divided in the plane,that are Beipu-Laoyemiao fault system,Gaoliu fault system,Baigezhuang fault system and Nanpu fault system.Among them,Gaoliu fault system and Nanpu fault system can be further divided into 2 and 3 sub-fault systems respectively.While,it can be divided into two fault systems vertically：lower fault system （E2s3 tectonic layer） and upper fault system （E2s1-Q layers）.There are four kinds of fault assemblages：＂parallel-like＂,＂parallel intertwined comb-like＂ and ＂broom-like＂.Cenozoic structural deformation of Nanpu sag can be reasonably explained with two-phases extension model：structural deformation of E2s3 era is caused by NW SE direction extension with Mesozoic pre-existing weaknesses,while structural deformation since E2s1 is caused by north-south direction extension with preexisting faults formed in E2s3 era,and E2s2 era is stress transition phase.There are significant segmentations in the sag boundary faults （Xinanzhuang Fault,Baigezhuang Fault and Gaoliu Fault）,the strike,properties,activation of different segments showed a significant difference,and significant changes occurred in the different stages of the tectonic evolution.The tectonic framework by the sag boundary faults,Nanpu Fault and Gatou Fault in sag played an important controlling role on the fault formation and evolution of Nanpu sag.The complicated pre existing faults were the root causes of lateral variation of fault system.