右江地区新生代断裂活动及构造变形机制的物理模拟分析

Physical simulation analysis of the Cenozoic fault activities and structural deformation mechanism of the Youjiang area

右江地区北西向断裂起源于晚古生代右江盆地内发育的同沉积断裂,这些断裂近等间距平行分布,新生代以来发生了多期次左旋走滑活动,进而导致了右江地区整体发生简单剪切变形。利用三维沙箱模型展开了物理模拟实验,对新生代右江地区的变形机制进行了分析。实验结果表明,早期在红河断裂的左旋剪切错动和印支地块的顺时针旋转联合作用下,右江地区北西向断裂复活,并发生明显的左旋走滑活动;随后川滇地块发生东南向的挤出运动,对右江地区产生侧向挤压,导致了右江地区北西向断裂新一轮的快速左旋走滑活动,同时还导致了右江地区西部的地壳压缩增厚。实验证实新生代右江地区的简单剪切变形以及北西向断裂的走滑活动是印支地块和川滇地块挤出运动共同作用的结果,同时也是印度-欧亚板块碰撞产生的连锁反应之一。

The NW-trending faults in the Youjiang area originated from synsedimentary faults developed in the Youjiang Basin of Late Paleozoic.In Cenozoic these equidistantly spaced faults have undergone multiple left-lateral strike-slip activities,which then led to a simple-shear deformation of the Youjiang area.A 3-D sandbox model is designed to study the deformation mechanism of the Youjiang area.The experimental results show that the NWtrending faults were reactivated and a strikingly left-lateral strike slip occurred under the left-lateral movement and the clockwise rotation of the Indochina block.And then the lateral compression of the Sichuan-Yunnan block resulted in a new round of fast left-lateral strike-slip of the NW-trending faults in the Youjiang area,and it also resulted in crustal compression and thickening in the western part of the Youjiang area.Both the left-lateral strikeslip activities of the NW-trending faults and the simple-shear deformation occurred in the Youjiang area in Cenozoic were driven by the extrusion of the Indochina Block and the Sichuan-Yunnan Block,and they can be viewed as one of the consequences of the India-Eurasia collision.