帕米尔突刺东缘冲断带构造形成机制:物理模拟及讨论

摘要

利用物理模拟实验,建立了两个不同边界条件的模型分别模拟帕米尔突刺东缘柯克亚?和田褶皱冲断带和喀什?叶城转换断层带的逆冲走滑构造演化过程,进而分析和讨论了研究区构造变形特征和变形机制.物理模拟实验结果表明:(1)帕米尔突刺东缘的柯克亚?和田褶皱冲断带和喀什?叶城转换断层带均形成于压扭应力场作用下,发育明显断层走滑现象,前者逆冲前缘断层兼具左行走滑特征,后者逆冲前缘断层则具右行走滑特征,但前者总体走滑量明显小于后者;(2)帕米尔突刺东缘的柯克亚?和田褶皱冲断带和喀什?叶城转换断层带走滑作用均主要位于山前边界断层带,越靠近逆冲前缘(盆地内部),走滑效应越微弱,挤压效应越明显;(3)在边界走滑断层前缘(往盆地方向),弧形断裂由挤压方向向前依次产生,并且斜向相交,验证了帕米尔东缘冲断带构造演化符合自南向北依次变新的规律;(4)在斜向压扭作用过程中,走滑断层构造带不一定发育明显的高角度甚至直立的断层,也可能表现为逆冲叠瓦构造楔样式,形成走滑逆断层,故在进行帕米尔突刺东缘(如塔西南山前)地震剖面构造解析时应充分关注这种构造类型.%Two models with different boundary conditions were carried out to simulate the structural evolution of the Kekeya?Hetian fold-and-thrust belt and Kashi?Yecheng strike-slip belt in the eastern margin of Pamir salient, respectively. The analogue modeling results show that: (1) Both of the Kekeya?Hetian fold-and-thrust belt and Kashi?Yecheng strike-slip belt in the eastern margin of Pamir salient were formed under compressive shearing. Strike-slip faults occurred within both of the belts, but the displacement of these strike-slip faults in the Kekeya?Hetian fold-and-thrust belt is less than that in the Kashi?Yecheng strike-slip be (2) The Kekeya?Hetian fold-and-thrust belt is mainly under the influence of compression stress with weaker shearing stress while the Kashi?Yecheng strike-slip belt is mainly under the influence of shearing stress with oblique compressive stress. The strike-slip faults are mainly located in the piedmont within these two belts. The effect of the strike-slip fault diminishes towards the front of the thrust belt (to the interior basin); (3) In the front of the boundary strike-slip faults (to the interior basin), the intersecting arc thrust faults occurred successively along the shortening direction. These structural features demonstrated that the structures evolved northwards in the eastern margin of Pamir salient; (4) The oblique compression does not necessarily result in high angle faults or vertical faults, whereas low-middle angle thrust faults with strike-slip displacement are also possible. Hence, more attention should be paid to such thrust faults during the structural analysis of seismic profiles in the eastern margin of Pamir salient (e.g. the structural belts in piedmont of western Tarim Basin).