Pre-existing structures (e.g., folds, foliations, lineations) are usually rotated and modified within a shear zone, depending on their attitude with respect to the kinematic framework (i.e., orientation of instantaneous stretching axes (ISA), kinematical vorticity number of the flow (W_k)) of the shear zone. In addition, new folds may also form within a shear zone, and it is not always easy to distinguish between the pre- and syn-shearing structures in the field, especially if they form on the same rock type. The present contribution describes the reorientation and shape modification (tightening) of pre-existing and syn-shearing folds in metamorphosed calcareous rocks of the Kumbhalgarh Group (part of Delhi Supergroup) due to shearing along the Ranakpur Shear Zone (RSZ), in Kumbhalgarh–Sayra–Ranakpur area of South Delhi Fold Belt (SDFB), also called South Delhi Terrane (SDT). From field-based study and measurements, it is shown that the shallow-plunging, upright second generation (DF₂) folds of SDFB/SDT have been rotated to subvertical, tight folds within the RSZ. Fold shape analysis using layer thickness and limb dip of folds (i.e., Ramsay’s classification) and by Fourier transform shape analyses of fold profile sections corroborates and roughly quantifies the tightening and shape modification of pre-existing folds within the RSZ. In contrast, syn-shearing folds have formed on the foliations in calc-silicate rocks which show strongly non-cylindrical geometry with apical deflection in an oblique direction. From the available shear sense indicators like rotated porphyroclast tails and vergence of asymmetric folds, the shear sense of the RSZ is interpreted as oblique reverse (east-side-up) with subordinate sinistral (east-towards-north) shear component, which is similar to the shear sense interpreted by some earlier workers.

先前存在的结构（例如褶皱，叶状结构，线条）通常会在剪切区内旋转和修改，具体取决于它们相对于运动学框架的态度（即瞬时拉伸轴（ISA）的方向，运动的涡度数）流（w ^ _ķ））的剪切区。另外，新的褶皱也可能在剪切带内形成，并且在田间的预剪切结构和同向剪切结构之间进行区分并不总是那么容易，特别是如果它们在相同的岩石类型上形成的话。本文稿描述了由于在昆布加尔邦的拉纳普布尔剪切带（RSZ）沿剪切作用，昆布加尔组（德里超群的一部分）的变质钙质岩中已存在的和同向剪切褶皱的重新定向和形状修正（收紧）。南德里折叠带（SDFB）的Sayra–Ranakpur地区，也称为南德里地形（SDT）。从实地研究和测量中可以看出，第二代浅俯冲直立（DF ₂）SDFB / SDT的折痕已旋转到RSZ内的垂直下折褶皱。使用层厚度和褶皱的肢垂度（即，Ramsay的分类）进行褶皱形状分析，以及通过对褶皱轮廓截面进行傅立叶变换形状分析，可以证实并大致量化RSZ中现有褶皱的收紧和形状修正。相比之下，钙硅酸盐岩石中的叶面上形成了同向剪切褶皱，这些褶皱显示出强烈的非圆柱几何形状，并在倾斜方向上出现了顶偏。根据可用的剪切感测指标，例如旋转的卟啉尾部和不对称褶皱的收敛，RSZ的剪切感被解释为斜向反向（东侧向上），具有次要的左向（东向北）剪切分量，这类似一些早期工人解释的剪切意义。