松辽盆地北部徐家围子断陷构造格局及其成因

徐家围子断陷形成于晚侏罗—早白垩世早期,是松辽盆地北部深层最重要的生气断陷.运用构造解析的方法,结合地质背景和应力环境分析,对徐家围子断陷的构造格局及其成因进行探讨.断陷期形成的地层中发育有近南北向(北北西、北北东向)伸展断裂、北东向—北东东向正断层、北北西向逆冲断层、北北西向褶皱、北东向褶皱、北东东向褶皱等多组构造形迹.除北东向褶皱为晚期北西—南东向挤压应力作用的产物,其它构造形迹均形成于断陷期.断陷期地层内发育的3个不整合被解释为断陷期构造幕式渐进变形的产物.徐家围子断陷的两凹一凸的构造格局受近南北向压扭应力场控制,其中平行于最大主压应力方向发育的左旋斜列低角度边界正断层控制了2个箕状断凹的形成,分隔这两个断凹的断凸的形成则与边界断裂的倾滑作用派生的局部挤压应力有关.

Tectonic framework of Xujiaweizi fault depression in northern Songliao Basin and its origin

Xujiaweizi fault depression formed from late Jurassic to the early stage of early Cretaceous,and it is the most important gas-bearing fault depression in northern Songliao Basin.The tectonic framework of the fault depression and its origin are discussed based on the interpretation of regional seismic profiles and the analyses of geological settings and paleo-stress environment.It is held that,SN-(NNW-or NNE-)strike normal faults,NE-or NEE-strike normal faults,NNW-strike thrusts,NNW-strike folds,NE-strike folds,and NEE-strike folds develop in the formation formed in the faulting stage.All of them,except the NE-strike folds,are generated during formation of the fault depression,and the NE-strike folds are the result of the extrusion in NW-SE orientation.Three major unconformities found in the strata deposited during the activity of faulting are ascribed to synchronic successive structural deformation. Xujiaweizi fault depression consists of two fault-sags and one fault-uplift,which is determined by the compressional——torsional stress field with near N-S orientation.Along maximum principal stress orientation,a set of sinistral en-echelon low-angle boundary normal fault is formed,which determines the formation of the two sags.The generation of the fault uplift is related with the local compression stress derived from the dip-slipping of the boundary fault.