The Trans-Himadri Detachment Fault (T-HDF) of the Kumaon region of western Himalaya, a north-easterly steeply dipping discrete brittle/semi-brittle fault, had previously been regarded as a strand of the South Tibetan Detachment System (STDS). Yet, elsewhere in the Himalaya, the STDS is defined as a diffuse, ductile low-angle normal-sense shear zone. This aspect of the STDS remained conjectural and was even refuted by various workers in the Goriganga valley in the Kumaon. We have systematically documented the STDS as a low-angle, northerly dipping, ductile, diffuse shear zone, with a true thickness of >5 km in this transect. In the present scenario, the shear zone is located only within the psammo-pelitic basal part of the Tethyan Sedimentary Sequence (TSS), and bypassed the rock units of the Greater Himalayan Sequence (GHS). Multiple grain-statistical parameters of mylonitized micaceous quartzites point to an anastomosing architecture which displays a single precursory damage zone and a wider core for the entire STDS shear zone. The ⁴⁰Ar*/³⁹Ar geochronology and oxygen isotope analysis of the micas in mylonites demonstrated that the STDS evolved in weak lithologies, between c.14–11 Ma, at ∼300–350 °C ambient temperature, at or immediately below the brittle-plastic transition depth in the quartzo-feldspathic continental crust.

Consideration of similar range of optimum ages of cessation of the extensional activity and already published timings of the end of brittle motion of the STDS in adjacent regions suggests that this wide diffuse shear zone is a deeper counterpart of the brittle upper STDS. This is in sharp contrast to the exposures of the detachment elsewhere in the Himalaya, where diffuse zone demonstrably constitutes the lower branch of this detachment. This finding has potential implications on overall understanding of the deformation related to the STDS and late Miocene geodynamic evolution of the GHS in this region.

喜马拉雅西部库马翁地区的跨喜马拉雅分离断层（T-HDF）是一条东北陡倾的离散脆性/半脆性断层，以前被认为是藏南分离系统（STDS）的一条。然而，在喜马拉雅的其他地方，STDS 被定义为一个扩散的、延展性的低角度正向剪切带。STDS 的这一方面仍然是推测性的，甚至被 Kumaon 的 Goriganga 山谷的各种工人驳斥了。我们系统地将 STDS 记录为一个低角度、北倾、韧性、扩散剪切带，在该样带中的真实厚度大于 5 公里。在目前的情景中，剪切带仅位于特提斯沉积层序（TSS）的沙泥质基底部分，并绕过了大喜马拉雅层序（GHS）的岩石单元。糜棱化云母石英岩的多个晶粒统计参数指向一个吻合结构，该结构显示出单个前体损伤区和整个 STDS 剪切带的更宽核心。这⁴⁰ Ar*/ ³⁹ Ar 年代学和糜棱岩中云母的氧同位素分析表明，STDS 在约 300-350 °C 环境温度下，在约 300-350 °C 的环境温度下，在约 14-11 Ma 之间，处于或低于脆性-石英长石大陆地壳的塑性转变深度。

考虑到类似的伸展活动停止的最佳年龄范围和已经公布的邻近地区 STDS 脆性运动结束的时间表明，这个宽的扩散剪切带是脆性上部STDS 的更深对应物。这与喜马拉雅其他地方的支队暴露形成鲜明对比，那里的扩散区明显构成了该支队的下部分支。这一发现对该地区与 STDS 和晚中新世地球动力学演化有关的变形的整体理解具有潜在意义。