This paper presents the geometric analysis of sigmoidal en echelon vein system that formed by non-coaxial deformation within conjugate Riedel-shear zones. Both sinistral S-type and dextral Z-type vein arrays, which have a subparallel enveloping surface, are observed. Individual asymmetric quartz veins consist of (1) a central, thin slickenfibre shear vein that is separating (2) pennant-shaped extensional vein tips characterised by strong dilation. Our observations closely resemble the results from published analogue experiments, which suggest that dilation occurs along R and R′ Riedel shear fractures during progressive rotation and slip within brittle-ductile shear zones. The shear vein formed by incremental pull-apart in the extensional step of overlapping R′ shear fractures, as marked by the presence of solid inclusion trails and bands. The pennant veins opened in the obtuse angle between intersecting R’ and R shears. The close association with a kinked pre-existing tectonic foliation, which acted as a passive marker of non-coaxial deformation, allows a kinematic restoration of the initial conjugate shear zone geometry that formed under approximate NE-SW compression. This model could warrant the reassessment of the classic interpretation of sigmoidal en echelon vein systems that are associated with kink bands.

本文介绍了共轭Riedel剪切带内非同轴变形形成的S形梯状脉系统的几何分析。观察到具有亚平行包络表面的左旋 S 型和右旋 Z 型静脉阵列。单个非对称石英脉由 (1) 一个中央的、薄的光滑纤维剪切脉组成，该剪切脉将 (2) 具有强烈扩张特征的三角旗形伸展脉尖端。我们的观察与已发表的模拟实验的结果非常相似，这表明在渐进式旋转和脆韧性剪切带内的滑动过程中，沿 R 和 R' Riedel 剪切裂缝发生膨胀。剪切脉在重叠的R'剪切裂缝的伸展步骤中由增量拉分形成，表现为存在固体包裹体痕迹和带。三角状脉在相交的 R' 和 R 剪之间的钝角处张开。与作为非同轴变形的被动标记的扭结的预先存在的构造叶理密切相关，允许运动学恢复在近似 NE-SW 压缩下形成的初始共轭剪切带几何形状。该模型可以保证对与扭结带相关的 S 形梯状静脉系统的经典解释进行重新评估。