冀中坳陷衡水–无极构造变换带的特征及其成因机制

构造变换带是调节两侧断层构造变形守恒产生的一种构造,是勘探潜在目标区、地震破裂的障壁区及油气易于聚集区,对其形成和演化研究具有理论和实践意义。本文通过对变换带形态、伸展参数和成因机制研究,得出以下结论:(1)衡水–无极构造变换带是控制、分隔冀中坳陷南区和中区伸展变形的一级构造变换带。太东断裂和沧西断裂在此转向或终止,其南、北构造明显不同;剖面上既有明显的花状构造,又有拆离滑脱构造,沿变换带还有岩浆活动,属于伸展型变换断层。(2)两侧伸展变形总体上南弱北强,变换带雏形于早白垩世产生,新生代经历了E_(1-2)k-E_2s_4启动期、E_2s_3-E_2s_2鼎盛期、E_3s_1-E_3d和N-Q定型期,其中差异伸展量最大的E_2s_3-E_2s_2期是主要形成时期。(3)先存构造奠定了变换带的基础,岩石圈分层拆离控制下沿太东断裂的差异伸展变形是主控因素,衡水断层新生代左行走滑为次要因素,最终使之成为一个传递伸展位移、兼具走滑和拆离性质并引发岩浆活动的特殊变换带。

Characteristics and Mechanism of Hengshui-Wuji Transfer Zone in Jizhong Depression

The transfer zone is a kind of structure that regulates the fault deformation of its two sides.It is a potential target area of oil-gas prospecting and barrier for seismic rupture,and therefore,study of its formation and evolution is of theoretical and practical significance.From the study of geometry,extension parameters and mechanism,the following conclusions can be drawn:(1) The Hengshui-Wuji Transfer Zone is the first level transfer zone which controls and separates the extending deformation of the southern and central areas of Jizhong Depression.The eastern faults of the Taihangshan Uplift (Taidong Fault) and western faults of the Cangxian Uplift (Cangxi Fault) are turned or terminated here,which resulted in the obviously different exhibition of the structures in the south and north areas.There are obvious flower structures,detachment structure,and magmatic activity along the transfer zone.The Hengshui-Wuji Transfer Zone belongs to an extensional transfer fault;(2) The extensional deformation is generally weak in the south and strong in the north,making a proto-transfer zone in Early Cretaceous.It experienced the initiation of E1-2k-E2s4,peak development of E2s3-E2s2,and formed in E3s1-E3d and N-Q.The main period of transfer zone formation is corresponded with the maximum extension difference in E2s3-E2s2 period;(3) The pre-existing structures laid the foundation for the Hengshui-Wuji Transfer Zone.The special transfer zone,which transmits extensional displacement with characteristics of strike-slip,detachment and triggering magmatic activity,was resulted mainly from the differential extensional deformation along the Taidong Fault since the Early Cretaceous related to the lithosphere layered detachment,and the sinistral strike sliping of the Hengshui Fault in Cenozoic may also have played a role in the process.