利用岩石磁组构恢复沉积盆地古构造应力场方法的探讨

DISCUSSION ON THE APPLICATION OF THE ROCK MAGNETIC FABRIC METHOD IN RESUMING PALEOTECTONIC STRESS FIELD IN SEDIMENTARY BASIN

由于缺少应力标志,沉积盆地覆盖区的古构造应力场定量恢复一直是个难题。为了探讨岩石磁化率各向异性在恢复沉积盆地古构造应力场的最大主应力方向方面的可行性,首先对岩石缓慢加压变形前后的磁化率各向异性的变化进行了实验研究,受力以后岩石的磁化率各向异性参数H,P,q值都相应增大,最大和最小磁化率主轴产状也有明显的变化,反映了浅层次的构造变形过程可对岩石磁组构产生明显的影响。然后,在塔里木盆地北部,将用最小磁化率主轴所求得的最大主压应力方位与用构造变形分析所求得的最大主压应力方向进行了对比分析,二者结果基本一致。说明在构造变形较强的沉积覆盖区(σ1),用岩石的最小磁化率主轴方向来确定沉积盆地古构造应力场的最大主压应力方位是可行的。最后,还对该方法的适应范围和构造应力场的分期等相关问题进行了讨论。

The quantitative resumption of the paleotectonic stress field in the sedimentary basin has long been a difficult problem due to the shortage of the stress symbols.In order to probe the feasibility of using rock magnetic anisotropy to resume the direction of the maximum principle stress of the paleotectonic stress field in sedimentary basin,an experiment has been made at first to investigate the change of the magnetic anisotropy before and after the rock is slowly pressurized and deformed.After the rock is pressurized,the magnetic anisotropy parameters of H,P and q increase accordingly,the maximum and the minimum principal axes of the magnetic susceptibility also change significantly,indicating that the tectonic deformation process in the shallow formation may exert obvious influences on the rock magnetic anisotropy.A comparison analysis between the direction of the maximum principal compression stress determined by the minimum principal axis of magnetic susceptibility and that determined by the tectonic deformation analysis were then carried out in the northern Tarim Basin.The results show that the two is roughly consistent,suggesting that,in the area with strongly deformed structures,it is feasible to use the direction of the minimum principle axis of magnetic susceptibility in determing the direction of the maximum principal compression stress of the magnetic susceptibility of the paleotectonic stress field in the sedimentary basins.At last,some related issues such as the applicable scope of this method and the stage division of the tectonic stress field have been discussed.