准噶尔盆地古生代末大地构造动力学数值模拟

Numerical simulation of tectonic dynamics of the Junggar basin at the end of Paleozoic

大地构造动力学数值模拟是构造物理研究的重要方向.本文利用有限元数值模拟方法研究准噶尔盆地古生代末的构造应力场.根据准噶尔盆地西部岩墙群和准噶尔盆地内部及周边地区应力标志,确定了晚二叠世准噶尔地区最大主应力方向为NW SE向,方位在295°左右,局部地区略有偏转.以实测古构造应力场为拟合标志,对Sengor和Allen提出的关于本地区演化的两种大地构造模式进行了构造应力场反演,从而为确定本地区晚二叠世比较合理的大地构造动力学机制提供限制.通过模拟对比发现,晚二叠世末准噶尔盆地可能处于张扭与压扭复合作用的大地构造动力学机制之下,即:盆地南北两侧的北天山断裂与额尔齐斯断裂为张扭性左行走滑断裂,而东西两侧的博格达山前断裂和达拉布特断裂是一对压扭性的右行走滑断裂系统,这两条断裂在晚二叠世准噶尔盆地古构造应力场的形成过程中起到了重要的作用.

Numerical simulation of tectonic dynamics is an important research issue oI tectonophysics. Using the finite element numerical simulation method, the paleostress field of the Junggar Basin at the end of Paleozoic was studied in this paper. On the basis of the study of dike swarms in the west of the basin and systematical analysis of other stress indicators in the basin and adjacent area, we acquire that the major direction of the principal stress in the study area in the late Permian is NW-SE （dominant strike is 295~）, with local direction deflects a little. With the observed palaeotectonic stress field as the criteria, a series of numerical simulations have been done based on the tectonic models proposed by ,Seng6r and Allen, aiming to provide constraints on the geodynamical mechanisms for the study area at the end of Paleozoic. The results indicate that the Junggar basin might form under the composite effect of tenso-shear and compresso-shear mechanisms. The Ertix fault on the northern margin of the basin and the north Tianshan fault on the southern margin are both tenso-shear sinistral strike-slip faults, while the Darabut fault on the western margin and the Bogda piedmont fault on the eastern margin are more likely compresso-shear dextral strike-slip faults, which played important role in the formation of the palaeotectonic stress field of the Junggar basin in late Permian.