Morphometric investigations on the NW Bitlis-Zagros mountain range (SE Turkey): Implications for the internal deformation of the western Turkish-Iranian Plateau

•Horizontal offset within the Bitlis-Zagros Mountain is larger than previous estimates.•Moderately to strongly asymmetric basins show no present uniform tilting direction.•Morphometric studies signify the uplift rate is larger than the horizontal slip rate.•Slow rate horizontal displacement since the beginning of the collision estimated.•The results support the shortening is being converted to the vertical plane strain. Collision of the Arabian and Eurasian plates has resulted in uplift of the Turkish-Iranian Plateau, where debate continues over how post-collisional convergence is being converted to strain. The internal deformation models of the plateau have taken into account the distribution of deformation in the NW-trending Bitlis-Zagros Mountain Range (BZMR), the southern boundary of the collision. The western end of the BZMR is marked by contrasting topographic relief resulting from the coupling of tectonic and erosional processes. This region providing an excellent record for undertaking quantitative analysis which can improve our understanding of its tectonic evolution. Mountain front analyses reveal that each fault segment located in front of the western BZMR falls within the limits of Class-1 that corresponds to an uplift rate of >0.5 mm yr−1. Hypsometric and basin asymmetry analysis were analyzed for 93 drainage basins, indicating that weakly to moderately eroded basins can be moderately to strongly asymmetric but show no uniform tilting direction. Channel concavity, integral and knickpoint analyses suggest that, apart from the thrust fault that represents the margin of the collision zone, there is no pronounced single geological constraint that causes differential tectonic uplift and furthermore implies that the effect is distributed across multiple different structures. The findings of this study suggest that continuous lower rate horizontal displacement has occurred in this region since the onset of collision, but also indicates that the western end of the BZMR represents a zone of higher convergence, in which shortening is being converted to the vertical plane strain.