两种结构类型的走滑相关剪断裂带

Two structural types of shear fracture belts related to wrenches

里德尔剪切是走滑带的典型构造样式,但近年来发现的很多剪断裂带中的剪断裂组合样式与经典里德尔剪切不同。在这些剪断裂带中,剪断裂的排列方式与两盘位移方向性质相同,即左阶左行或右阶右行,被称为同阶行剪断裂,其叠合部位具有离散性质。基于库伦破裂准则,认为这些剪断裂带是在双剪切带夹持的断夹块上发育的。在双剪切作用下,最大主应力迹线方向上将产生2组共轭势剪破裂,在递进变形过程中,与最大剪应力(主走滑方向)成小锐夹角的剪破裂将优先得到发展,而与最大剪应力成大锐夹角的剪破裂将受到抑制而被限制在前者之间,形成一种不同于经典里德尔剪切组合样式的新型剪断裂带。这种类型的剪断裂带发育离散型叠合带,对成藏成矿具有重要意义。

Riedel shears are the typical structural styles in strike-slip belts. However, shear fracture zones have been found recently to have different shear fracture assemblages. In these shear fracture belts, the properties of the arraying patterns of the shear fractures are identical with those of the moving ways of the two fault blocks, which is either left-step with left-lateral movement or right-step with right-lateral movement. The shear fractures are called homo-step-slip ones. These oversteps between two shear faults are divergent.Based on the Coulomb fracture theory, it is suggested that the shear fracture belts would be formed in the fault blocks between two wrench belts. In these cases, two conjugate potential shear faults would be formed along the maximum principal stress trajectories. In the progressive deformation, the shears with smaller acute angle to the maximum shear stress(principal strike-slip) trajectories have priority to develop. The shears with bigger acute angle to the maximum shear stress trajectories would be delimited between the former shears. A new-type shear fracture belt is formed different from the typical Riedel shears in shear fracture assemblages. This shear fracture belt will be favorable for both hydrocarbon accumulation and mineral deposit formation due to the divergent oversteps.