Abstract The Himalayan front exhibits varying convergence rates along its length. This study examines the morphotectonic evolution of the landforms in an intermontane valley (viz., Chitwan dun) present in a relatively rapidly converging segment of the Himalaya. Using field investigations, geomorphic analysis, and geochronology, we demonstrate that five geomorphic levels have developed in the past >112 ka. Four major phases of aggradation occurred in the Chitwan, i.e., >112 ka, ~112–>70 ka, ~70–25 ka, and ~18–11 ka. Tectonic activity on the Jharahi (JHT) and Belani thrusts (BT) at >112 ka and >70 ka respectively resulted in the uplift of the geomorphic units to Level 5 and Level 4. Continuous aggradation in the valley occurred between 70 and 25 ka (Level 3); the tectonic activity during this period is marked by the reactivation of the West Chitwan thrust (WCT) and the Central Churia Thrust (CCT). The Level 3 surfaces were abandoned during the LGM (25–18 ka) and subsequently incised. Enhanced monsoon in the post-LGM period favored aggradation of the Level 2 and 1 geomorphic units. The Level 2 surfaces were abandoned due to activity on the Danda (DT) and Shaktikhor Thrusts (ST) whereas the Level 1 landforms were incised due to climatic changes in the Holocene. Comparing the results of this study with other parts of the Himalaya, we infer that despite variable tectonic convergence rates, major aggradation and incision cycles are uniform. This suggests that Late Quaternary climatic perturbations have strongly influenced the fluvial systems across the Himalaya. However, the role of tectonics is also manifested in the form of multiple levels of surfaces and terraces.

中文翻译：

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探索气候和构造在喜马拉雅中部奇旺山间山谷地貌演化中的作用

摘要 喜马拉雅锋沿其长度表现出不同的收敛速度。本研究考察了喜马拉雅相对快速收敛段中的山间谷地（即奇旺丘）地貌的形态构造演化。通过实地调查、地貌分析和地质年代学，我们证明在过去的 112 ka 中已经发展了五个地貌水平。Chitwan 发生了四个主要的加成阶段，即 >112 ka、~112->70 ka、~70-25 ka 和~18-11 ka。Jharahi (JHT) 和 Belani 逆冲断层 (BT) 的构造活动分别 >112 ka 和 >70 ka，导致地貌单元抬升至 5 级和 4 级。 70 和 25 ka 之间发生山谷连续加积（级别 3)；这一时期的构造活动以西奇旺逆冲断层 (WCT) 和中央丘里亚逆冲断层 (CCT) 的重新激活为标志。3 级表面在 LGM（25-18 ka）期间被废弃，随后被切割。后 LGM 时期季风增强有利于 2 级和 1 级地貌单元的集聚。由于 Danda (DT) 和 Shaktikhor Thrusts (ST) 的活动，Level 2 地貌被废弃，而 Level 1 地貌由于全新世的气候变化而被切割。将这项研究的结果与喜马拉雅山的其他部分进行比较，我们推断尽管构造收敛速度可变，但主要的加成和切割周期是一致的。这表明晚第四纪气候扰动强烈影响了喜马拉雅山脉的河流系统。然而，