Tectonic and climatic controls on topographic spatial variability across the Pamir Plateau and implications for drainage evolution

Abstract

The Pamir Plateau, NW prolongation of the Tibetan Plateau, experienced late Cenozoic thrusting and extensional shearing/faulting and mainly receives moisture from the mid-latitude Westerlies. Thus, this region provides a natural laboratory to study how tectonic activity and climate impact topography. In this study, we extracted geomorphic indices from digital elevation model data, including local relief, normalized channel steepness index (k_sn), river longitudinal and χ profiles, as well as cross-valley profiles, to reveal the topographic variations across the Pamir Plateau, and to analyze the effects of tectonic activity and climate on its topography. Because the upper reaches of the Panj, Ghez, and Tashkurgan river catchments, and the Karakul Lake endorheic catchment are located in extremely low precipitation regions and dominantly result from late Cenozoic crustal extension, they generally have low local relief and k_sn values, gentle gradients on the χ-elevation plots, and wide valleys, especially along the intermontane basins. By contrast, the lower reaches of the Panj, Ghez, and Tashkurgan catchments generally have high local relief and k_sn values, steep gradients on the χ-elevation plots, and narrow V-shaped, deeply-incised valleys. For the lower reaches of the Panj catchment in the western Pamir, this difference is due to relatively high precipitation from the Westerlies, but for those of the Ghez and Tashkurgan catchments in the eastern Pamir, although they receive low precipitation, they cross the footwall of the Kongur Shan normal fault, along which tectonic uplift rates are particularly high. During the past ∼ 25 Ma, the drainage divide between the Panj catchment and the Ghez and Tashkurgan catchments migrated eastwards from the Pamir Plateau interior to its present location along the eastern Pamir Range, driven by high precipitation and erosion to the west.