Uplift history and landscape evolution along the northwest margin of the Iranian Plateau (Talesh Mountains) in the Arabian–Eurasian collision zone

To comprehend the evolution of a landscape in response to intraplate crustal deformation over long timescales, it is necessary to investigate the interactions between tectonics, climate, and lithology. Isolating the role of each factor gives rise to a better understanding of landscape evolution. In this respect, the Talesh Mountains, which are a prominent tectonic range in the NW of the Iranian Plateau and formed by compressional stresses owing to the Arabia-Eurasia continental collision, provide a unique case study to explore the interplay between tectonics and surface processes. The range shows a transient landscape resulting from a combination of several tectonic events from the Eocene to the Pliocene, rainfall variability and rock strength contrasts. To date, the main governing agents of the present-day architecture of landscape have not been fully studied. We therefore combined geomorphological field surveys with quantitative analyses of the regional topography, geomorphology and stability of the main drainage divide, stream profile analysis and denudation rates using meteoric ¹⁰Be to decipher the surface deformation, uplift mechanism and drainage divide evolution. Additionally, an inverse modelling of the river longitudinal profiles was performed to reconstruct the base level fall history of the region, providing insights into the timing of the rock uplift rates and geodynamics of the NW margin of the Iranian plateau. Our results document contrasting erosion rates ranging from ⁓ 100 to 400 m/Myr, with lower values in the more arid plateau interior, and higher values on the wetter plateau exterior. These rates correlated well with topographic metrics. The spatial pattern of erosion rates showed that the drainage networks of the eastern flank of the range, and along the plateau margin are eroding about twice as fast as those in the plateau interior. These contrasting erosion rates triggered the divide migration towards the plateau interior. Our inverse modelling of river longitudinal profiles of the plateau exterior indicated a progressive increase in the relative rock-uplift rates which reached its peak to ⁓0.5 mm/yr from ⁓5 to 3 Ma. For these documented uplift rates there are two different processes: (i) a kilometer-scale base level drop of Caspian Sea driven by eustasy and changes in regional tectonics, and (ii) localized thrusting and rock uplift along the eastern flank of the range. The combined effect of these processes results in a significant relative base level fall. This event accelerated the bedrock river incision in the Talesh Mts. The differences in erosion rate across the divide are indicative of a long-wavelength morphological disequilibrium and landscape transience in response to asymmetric uplift and feedback of surface processes driven by climate together with lithological characteristics.