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The Mountain Front Flexure marks a dominant topographic step in the frontal part of the Zagros Fold–Thrust Belt. It is characterized by numerous active anticlines atop of a basement fault. So far, little is known about the relative activity of the anticlines, about their evolution, or about how crustal deformation migrates over time. We assessed the relative landscape maturity of three along-strike anticlines (from SE to NW: Harir, Perat, and Akre) located on the hanging wall of the Mountain Front Flexure in the Kurdistan Region of Iraq to identify the most active structures and to gain insights into the evolution of the fold–thrust belt. Landscape maturity was evaluated using geomorphic indices such as hypsometric curves, hypsometric integral, surface roughness, and surface index. Subsequently, numerical landscape evolution models were run to estimate the relative time difference between the onset of growth of the anticlines, using the present-day topography of the Harir Anticline as a base model. A stream power equation was used to introduce fluvial erosion, and a hillslope diffusion equation was applied to account for colluvial sediment transport. For different time steps of model evolution, we calculated the geomorphic indices generated from the base model. While Akre Anticline shows deeply incised valleys and advanced erosion, Harir and Perat anticlines have relatively smoother surfaces and are supposedly younger than the Akre Anticline. The landscape maturity level decreases from NW to SE. A comparison of the geomorphic indices of the model output to those of the present-day topography of Perat and Akre anticlines revealed that it would take the Harir Anticline about 80–100 and 160–200 kyr to reach the maturity level of the Perat and Akre anticlines, respectively, assuming erosion under constant conditions and constant rock uplift rates along the three anticlines. Since the factors controlling geomorphology (lithology, structural setting, and climate) are similar for all three anticlines, and under the assumption of constant growth and erosion conditions, we infer that uplift of the Akre Anticline started 160–200 kyr before that of the Harir Anticline, with the Perat Anticline showing an intermediate age. A NW-ward propagation of the Harir Anticline itself implies that the uplift has been independent within different segments. Our method of estimating the relative age difference can be applied to many other anticlines in the Mountain Front Flexure region to construct a model of temporal evolution of this belt. [ABSTRACT FROM AUTHOR]

The NW segment of the Zagros Mountain Front Flexure in the Kurdistan Region of Iraq forms a prominent topographic and structural step separating the High Folded and Foothill zones. Due to scarcity of subsurface data, the geometry of faults underlying this flexure and the degree of basement involvement are poorly constrained. To overcome this, we estimated the structural relief along seven transects across the belt and reconstructed deformed geometries using balanced cross-sections. The average structural relief for six transects is around 2.6 km. Iterative kinematic forward modeling along one of these transects suggests that a multi-stage evolution involving both thin- and thick-skinned deformation can explain the observed structural relief. Our preferred model shows that early detachment folds in the Mesozoic to Neogene succession were overprinted by a NE-dipping basement-rooted thrust system with a cumulative displacement of 6.5 km. Up-dip, the basement thrust bifurcates into two splay thrusts. While the structurally higher splay accommodated 4.2 km of slip and amplified frontal anticlines to form the Mountain Front Flexure, the lower and younger splay took up 2.3 km of slip, which was mainly transferred into the Triassic basal detachment of the Foothill Zone. The shortening across the NW Zagros is calculated at c. 24.8 km. The shortening amount within the topographically low part of the belt implies that the Late Miocene to Quaternary shortening rate was much lower than the geodetically derived convergence rate. • The structural relief across the NW segment of the Zagros Mountain Front Flexure is 2.4–3 km. • A balanced cross-section reveals 6.5 km reverse displacement on abasement thrust below the Mountain Front Flexure. • The shortening along a regional cross-section is c. 24.8 km. The L. Miocene-Quaternary shortening rates in the belt were much lower than geodetically derived convergence rates. [ABSTRACT FROM AUTHOR]