海拉尔盆地红旗凹陷早白垩世构造特征与变形期次的厘定

Structural Features and Determination of Deformation Stages of Hongqi Sag in Hailar Basin During the Early Cretaceous

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,总体上呈北东向展布,由三坳、两隆5个一级构造单元组成,自西向东依次为扎贲诺尔坳陷、嵯岗隆起、贝尔湖坳陷、巴彦山隆起和呼和湖坳陷,其中红旗凹陷是位于贝尔湖坳陷北部的一个二级构造单元。研究表明,红旗凹陷在早白垩世经历了4个变形阶段:在早白垩世兴安岭群-南屯组沉积时期为NW-SE向伸展作用阶段,形成以大型犁式正断层为控陷断层的NE向箕状半地堑;在大磨拐河组-伊敏组一段沉积时期为NW-SE向挤压作用阶段,使早期控陷正断层发生强烈的反转作用而转化为逆断层,靠近控陷断层的NW边界由于断层上盘的逆冲而隆升,凹陷的SE斜坡带由于控陷断层在反转作用过程中深部的逆冲滑移在浅部受阻而发生的旋转式隆升,使凹陷的规模发生明显萎缩,并在凹陷的中部形成大型NE向断层转折褶皱,构成了红旗凹陷的中部断隆带;在伊敏组二段下部沉积时期为近EW向伸展作用阶段,早期控陷断层表现出正断层的特征,新形成的NE向控陷断层具有左行离散型走滑的性质;在伊敏组二段上部沉积时期为近EW向挤压作用阶段,早期控陷断层再次表现为上盘逆冲的特征,在断层上盘、靠近断层的部位形成反转背斜,并在凹陷中形成断层转折褶皱。在每一变形阶段中,红旗凹陷的构造特征在空间上存在一定的差异。

Hailar basin is a meso-cenozoic basin which superimposed on the Inner Mongolia-Greater Hinggan Mountain Paleozoic collision orogenic belt.The north-east trending basin consists of five first-order structural units（three depressions and two uplifts） including Zhalenuoer depression,Cuogang uplift,Beier Lake depression,Bayanshan uplift and Huhe Lake depression from west to east,respectively,The Hongqi sag is a second-order structural unit in the north of Beier Lake depression.Research indicates that the Hongqi sag underwent four deformation stages during the Early Cretaceous： Stage of NW-SE extension during the deposition of Xing’anling Group and the Nantun Formation,NE trending half-garben controlled by large scale dustpan-like normal fault as depression-controlling fault developed;Stage of NW-SE compression during the deposition of Damoguaihe Formation and the first member of Yimin Formation,thrust fault formed due to the intensive inversion of early normal fault,the thrust of the hanging wall lead to the uplift of the NW boundary of the sag near the depression-controlling fault,and the block of thrust sliding of the deep part of the depression-controlling fault in the shallow area lead to the rotary uplift of the SE slope zone during the inversion,hence,the size of the sag dwindled obviously,and the large scale NE trending fault-bend fold formed in the center of the sag which consists of the central fault-uplift zone of Hongqi sag;Stage of EW trending extension during the deposition of lower part of the second member of Yimin Formation,the early depression-controlling fault showed features of normal fault,and the newly formed depression-controlling fault had features of sinistral discrete slip;Stage of EW compression during the deposition of upper part of the second member of Yimin Formation,the early depression-controlling fault showed features of thrust of hanging wall again,inverted anticline developed in the hanging wall near the fault,forming fault-bend fold in the sag.During each deformation stage,there were some differences of the structural features of Hongqi sag in space.