东辛地区营26断层变换带形成机制模拟

Forming mechanism simulation of Ying 26 transfer zone in Dongxin area

为了分析叠覆型断层变换带的形成机制,揭示变换带内断裂体系的发育规律,根据区域应力机制设计相应的张扭及底辟复合作用实验装置,从湿度不同的砂、黏土及砂泥混合物中选取微湿的细砂作为实验材料,并与应力场数值模拟相结合,对东营凹陷东辛地区营26变换带沙河街组沉积期进行构造物理模拟。结果表明:营1与营31断裂是沙河街组沉积前由NE10°的伸展作用同时形成的两条平行断裂,二者向两侧的伸展位移在叠覆带边缘诱导出一条与伸展方向呈50°斜交的张扭性变换断层,随着二者叠置程度的增大,变换断层的发育程度也增大。之后,区域性的右旋走滑运动形成一系列雁列式分布的变换断层,其优势走向与剪切应力场方向一致,后期的底辟作用加剧了断裂系统的复杂程度。断层的转折端、交汇和分叉处以及次级断层形成的局部小断块内,最大主应力和最小主应力差值较大,为低级序断层的优势发育区。另外,平面上斜交的剪切断层在不同方向的走滑活动造成的局部断块的掀斜运动加剧了低级序断层复杂程度。

An tenso-torsional experimental apparatus with diapirism is designed for Ying 26 overlapping transfer zone formed during Shahejie Formation depositional stage in responding to the regional stress field in Dongxin area,Dongying sag.The aim is to simulate the formation mechanism and to reveal the law of distribution and development in the fracture system.Moist arentilla is chosen as the experimental material from the sand,clay and their mixture with different moisture.Experimentation process is filmed in detail and interpreted accurately.The results of the experiment show that：The Ying1 fault and Ying31 fault did not result from an early fault dislocated by lately transfer fault;instead they formed as two parallel faults before the deposition of Shahejie Formation under the effect of the extension in about NE10°.As pre-existing faults,the extensional displacement of the two faults induced the first shearing transform fault in the transfer zone.The fault strike of transform fault is oblique with the stretching direction with 50-degree angle.The higher the overlap ratio of the two faults,the more developed the transfer fault.Then dextral strike slipping formed a series of en-echelon faults and the dominant strike direction is in accord with the direction of shear stress field.At last,the diapirism complicated the fracture system in the late stage.Low-grade faults grew mostly on the cross,round and the crotch of faults,especially in small blocks closed or semi-closed by secondary faults due to large differences between minimum and maximum principal stress in this area.In addition,shear faults are oblique in the plane and strike-slip in different directions,forming tilted local blocks.As a result,the distribution of low-grade fault is more complex.