松辽盆地南缘长岭凹陷断陷层的构造特征与应变模式

Tectonic feature and strain pattern of Changling sag on the southern edge of Songliao basin,China

以松辽盆地南缘的长岭凹陷断陷层为对象,采用构造-地层分析方法,在确定盆缘断裂活动期次、样式及由沉积记录示踪的构造变形的基础上,进一步通过系统的二维构造-地层平衡剖面恢复,揭示出在长岭凹陷断陷层的发育过程中,盆地伸展方向存在自NE—SW向至近EW向的顺时针旋转。旋转主要发生于下白垩统沙河子组形成时期。位于松辽盆地中央凹陷带南端的长岭凹陷由于构造部位的特殊性,在形成的早期表现出较明显的北东向伸展断陷的特征,并与后期北西向的构造伸展相叠加,形成了较复杂的构造样式。在盆地伸展的过程中,存在应变机制的转变,早期以纯剪变形为主,以发育地堑式伸展构造样式为特征;后期以简单剪切变形为主,以发育半地堑式伸展构造样式为特征。

By means of structure-stratigraphy method, based on the knowledge of faulting active phase, pattern of the basin edge as well as tectonic deformation traced by deposition record, with the help of systematic 2 dimension structure-stratigraphy balance recovery, it＇s indicated that during the developing process of Changling sag, there was clockwise rotating from NE-SW to EW along the expanding direction.This movement generally happened at the same time as formation of Lower Cretaceous Shahezi Group. Because of the special tectonic location of Changling sag on the southern edge of central Songhao basin, in this early stage, noticeable northeast expanding depression overlapped later northwest tectonic expanding, which leads to comphcated tectonic pattern. During the extension period of Changling sag, strain pattern changed from pure shear which caused graben-type extension structural pattern developed in the early stage to simple shear formed half-graben-type in later.