伸展边界方向对伸展盆地正断层走向的影响——来自平面砂箱实验的启示

INFLUENCES OF DIRECTION OF EXTENSIONAL BOUNDARY ON STRIKES OF NORMAL FAULTS IN EXTENSION BASIN: INSIGHTS FROM PLANE SANDBOX EXPERIMENTS

五种不同边界几何条件的平面砂箱实验模型表明 ,一个方向的伸展变形可因伸展边界方向的变化形成不同走向的正断层 ,伸展裂陷盆地中不同走向的正断层并非一定代表不同方向区域构造应力作用、或多期构造变形的结果。伸展裂陷盆地正断层走向受伸展边界走向和构造伸展的方向共同控制 ,伸展边界的控制力随距离增大而逐渐衰减。伸展边界附近的断层走向主要受伸展边界方向控制 ,大致反映伸展边界方向。盆地内部断层走向主要受构造伸展方向控制 (趋向于垂直构造伸展方向 ) ,主要反映构造伸展方向。盆地伸展边界方向的变化可以引起伸展裂陷盆地内部断层走向的转向。因铲式正断层上盘滚动变形产生的正断层 ,其走向平行于铲式边界断层的走向。

In this paper influences of boundary directions on strikes of normal faults in extension basin are discussed according to five planar sandbox experimental models of different boundary geometries. The dimension of rig used in this study is 150(length)×40(width)×20(highness)cm. Incohesive dry quartz sand of 300-600uaverage grain size is used in experiments, which has a linear Navier-Coulomb behaviour with inner friction angles of 31 to 33°.Experiments are conducted in constant displacement rates of 4 48×10 -3 s -1 -8 33×10 -3 s -1 . It is indicated that extensional deformation of one direction can produce normal faults of different strike directions because of variation in directions of extensional boundary. Normal faults of different strikes in extensional rifting basins are not surely caused by regional tectonic stresses of different directions or structural deformations of multiphase. Strikes of normal faults in extensional rifting basins are dependent on the direction of extensional boundary and the tectonic extension direction. Effects of extensional boundary decrease with increase in distances from the boundary. Strikes of normal faults near extensional boundary are controlled mainly by its directions and can approximately reflect them. Strikes of normal faults in inner parts of the extensional rifting are mainly controlled by tectonic extensional direction and trend to the direction normal to it and mainly reflect extensional direction. Variations in directions of extensional boundary of rifting basins can cause changes of strikes of normal faults. Strikes of the normal faults caused by roll-over deformation above listric normal faults are constantly parallel to strikes of boundary faults.