海拉尔盆地乌尔逊凹陷构造变形对沉降中心迁移的控制

海拉尔盆地是叠置于内蒙-大兴安岭古生代碰撞造山带之上的中、新生代盆地，乌尔逊凹陷是海拉尔盆地中部的1个二级构造单元，自早白垩世开始，经历了3次伸展作用、2次挤压作用，盆地中地层厚度和沉降中心的迁移主要受同生断层和与之伴生的断层相关褶皱所控制。在伸展作用时期：当发育1个犁式正断层，在其上盘形成1个箕状断陷，沉降中心位于断层上盘、靠近断层的区域，在伸展量较大的部位形成1个或多个沉降中心；当发育多个控陷正断层，在其上盘形成多个相互独立的箕状断陷，但每一个断陷都有各自的沉降中心，不同方向断层的交汇部位往往就是断陷的沉降中心。随着伸展量的增大，断陷的沉降中心不断向控陷正断层滑动的相反方向迁移，盆地的规模也随之增大。在第一次挤压作用中，早期NS向控陷断层F₁发生反转作用，其上盘靠近断层的部位发生隆升，远离断层的部位作为大型断层传播褶皱背斜前翼也发生旋转式隆升，乌尔逊凹陷成为NS向大型断层传播褶皱背斜的前翼向斜，地层的沉积厚度在靠近断层的部位和远离断层的部位都很薄；向大型断层传播褶皱背斜前翼向斜部位，地层的沉积厚度逐渐增大，盆地的沉降中心向向斜的低洼区域迁移。在第二次挤压作用中，早期NS向控陷断层F₂发生反转作用，在乌尔逊凹陷中部形成1个规模较大的NS向断层传播褶皱背斜或突发构造，背斜或突发构造的顶部被剥蚀，盆地的沉降中心位于中部背斜带前、后翼向斜的低洼区域。

Structural Deformation Control over the Subsidence Center Migration of Wuerxun Sag in Hailar Basin

Hailar basin is a Meso-Cenozoic basin which superimposed on the Inner Mongolia-Greater Hinggan Mountain Paleozoic collision orogenic belt. Wuerxun sag which is a second-order structural unit in the middle part of Hailar basin, has been experienced 3 times extension and 2 times compression since the Early Cretaceous. The stratigraphic thickness and migration of subsidence centers in Wuerxun sag are mainly controlled by syngenetic fault and fault-related fold. On the extension period, when a half-graben formed on the hanging wall of the listric normal fault, one or more subsidence centers which located in hanging wall of the fault and near the fault formed at the part of the fault that the stretching amount is lager than the other part; When the multiple independent half-grabens formed on the hanging wall of the listric normal faults, every half-graben has its own subsidence center, and the intersection of different direction faults is often the subsidence center of the fault depression. With the increase of stretch amount, the subsidence center of the fault depression constantly migrated to the opposite direction of the slip direction of the control subsidence fault, and the scale of the basin gradually increased. On the first compression period, the early NS trending control subsidence fault F₁ reversed, the hanging wall near the fault occurred uplift, and the part away from the fault, as the front limb of a large fault-propagation fold anticline, also occurred rotary uplift. Wuerxun sag became the front syncline of a large NS trending fault-propagation fold anticline, the stratigraphic thickness is very thin near the fault and away from the fault, the stratigraphic thickness gradually increases to the front syncline of the large fault-propagation fold anticline, and the subsidence center migrates to the low-lying areas of the syncline. On the second compression period, the early NS trending control subsidence fault F₂ reversed, a large-scale NS trending fault propagation fold anticline or pop up formed in the middle part of Wuerxun sag. The top of the anticline or pop up were eroded, and the subsidence centers located in the low-lying area of the front and rear synclines.