The mechanical properties of detachment zones significantly influence the geometry, structural style, and amount of shortening in the fold and thrust belts. The shale layers in a sedimentary package can act as a detachment zone at different levels of a fold and thrust belt. Detachment zones are not exposed in the active fold and thrust belts, making the detailed study of these detachment zones impossible. This situation makes it difficult to know the architecture and main deformation mechanisms. In this work, we use detailed structural analysis to investigate deformational mechanisms of an ancient and exhumed detachment zone in the Mexican Fold and Thrust Belt, in central Mexico, as an analogue to active modern-day examples. We describe the architecture of the detachment zone through detailed field mapping, strain measuring, and vorticity analysis. Our observations suggest that the studied shear zone is an upper-level detachment zone developed during the Late Cretaceous-Paleogene orogeny. The upper-level detachment zone accommodates the deformation through brittle-ductile structures related to localized mylonitic foliation, s-c structures, duplexes, sheath folds and reverse faults. The mesoscopic structures described in the shear zone suggest a heterogeneous shear deformation. The kinematic vorticity values (W_k = 0.73 in average) and the strain data (R_XZ ~3 in average) suggest a sub-simple shear mechanism of deformation. Our results show the role of weak layers during the contraction of a sedimentary package and demonstrate the presence of simple and pure shear mechanisms in the development of the complex detachment zones in fold and thrust belts.

分离带的机械性能会显着影响褶皱和冲断带的几何形状，结构样式和缩短量。沉积包裹中的页岩层可以在褶皱和逆冲带的不同高度处作为分离区。分离区没有暴露在活动褶皱和冲断带中，因此无法对这些分离区进行详细研究。这种情况使得很难知道其结构和主要变形机理。在这项工作中，我们使用详细的结构分析来研究墨西哥中部墨西哥褶皱和冲断带中一个古老的，已掘出的脱离带的变形机制，以此作为现代活动实例的模拟。我们通过详细的现场测绘，应变测量和涡度分析来描述分离区的体系结构。我们的观察结果表明，所研究的剪切带是晚白垩世-古生代造山过程中形成的高层脱离带。上层脱离带通过与局部的lon状叶子，sc结构，双相，鞘褶和逆断层有关的脆性-延性结构来适应变形。剪切带中描述的介观结构表明剪切变形是不均匀的。运动涡度值（W 剪切带中描述的介观结构表明剪切变形是不均匀的。运动涡度值（W 剪切带中描述的介观结构表明剪切变形是不均匀的。运动涡度值（W 平均_k = 0.73）和应变数据（平均R _XZ〜3）表明了变形的简单剪切机制。我们的结果显示了薄弱层在沉积包裹收缩过程中的作用，并证明了在褶皱带和逆冲带中复杂分离带的发展过程中存在简单和纯剪切机制。