Documenting the structural evolution of the Himalayan orogen is fundamental for understanding the dynamics of collisional orogenesis. We argue that the importance of deformation in the frontal, Lesser Himalayan–Subhimalayan (LH-SH) portion of the Himalayan thrust belt for driving crustal thickening over the past ~15–13 m.y. has long been overlooked. To quantify its contribution to thickening, we measured parameters from 22 published cross sections that span the length of the orogen. The mean structural uplift accomplished by the LH-SH thrust belt increases from 10–15 km in the eastern half of the orogen to 15–23 km in the western half. An antiformal culmination constructed by LH duplexing is observed across the orogen and increases in structural height (to as much as 15–20 km) and north-south width moving westward. Construction of the culmination was the primary mechanism for building and maintaining wedge taper. The westward scaling of culmination size is accompanied by doubling and tripling of LH-SH shortening and accretion magnitude, respectively; when combined with a consistent orogen-wide modern taper angle (11° ± 2°), this indicates that duplexing facilitated the growth of an overall larger orogenic wedge moving westward. Following the initial southward propagation of deformation into LH rocks at ca. 15–13 Ma, the Himalayan orogenic wedge has been characterized by stacking of multiple thin, small-displacement thrust sheets to develop a high-taper orogenic wedge. Thus, LH-SH deformation has had a profound effect on driving thickening, exhumation, and the attainment of high elevations since the middle Miocene.

中文翻译：

---

小喜马拉雅-次喜马拉雅逆冲带的构建：中中新世以来喜马拉雅造山带增厚、剥露和高海拔的主要驱动力

记录喜马拉雅造山带的结构演化是了解碰撞造山动力学的基础。我们认为，在过去的 15-13 年间，喜马拉雅逆冲带的前部小喜马拉雅-次喜马拉雅 (LH-SH) 部分变形对推动地壳增厚的重要性长期以来一直被忽视。为了量化其对增厚的贡献，我们测量了横跨造山带长度的 22 个已公布横截面的参数。LH-SH逆冲带完成的平均构造抬升从造山带东半部的10-15km增加到西半部的15-23km。在整个造山带上观察到由 LH 双工构造的反形式顶点，并且结构高度增加（多达 15-20 公里），南北宽度向西移动。顶点的构造是建立和保持楔形锥度的主要机制。顶点大小的西移伴随着 LH-SH 缩短和吸积量分别增加一倍和三倍；当与一致的造山带宽现代锥角（11°±2°）相结合时，这表明双重作用促进了整体更大的造山带向西移动的楔形的生长。在变形最初向南传播到 LH 岩石之后。15-13 Ma，喜马拉雅造山楔的特征是堆叠多个薄的、小位移的推力片，形成一个高锥度的造山楔。因此，自中中新世以来，LH-SH 变形对驱动增厚、折返和达到高海拔产生了深远的影响。