LAUSR

ABSTRACT 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, this 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 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.