The Zagros Mountain Front Flexure in Kurdistan Region of Iraq: Structural style and Late Pleistocene-Holocene Fault Slip Rates Derived from Structural Modeling and Luminescence Dating of River Terraces

The Zagros Mountain Front Flexure (MFF) makes a prominent topographic and structural step along the Zagros Fold-Thrust Belt that accommodates a significant amount of shortening between the Eurasian and Arabian plates. Here, the structural style below the MFF in the Kurdistan Region of Iraq was reconstructed using balanced cross-sections and forward modeling, and Late Pleistocene-Holocene fault-slip rates were calculated across several structures using luminescence dating of river terraces along the Greater Zab River. A balanced and retro-deformable cross-section for the NW Zagros reveals that reverse displacement on a basement fault underlying the MFF, along with fault-related folding above the Triassic detachment, is indispensable to explain the observed structural relief. The uplift rates of river terraces, obtained from their elevation and ages, indicate ongoing slip on faults when integrated with the kinematics of fault-related folds for the structures. The basement fault underlying the MFF accommodates 1.46±0.60 mm a-1 of slip, while a more external basement fault further to the SW is accommodating less than 0.41±0.16 mm a-1. Horizontal slip rates from detachment folding above the Triassic detachment in two anticlines (Sarta and Safin) within the Zagros Foothills are 0.40±0.10 and 1.24±0.36 mm a-1, respectively. Balanced cross-section, distribution of river terraces, and regional topography indicate that basement thrusting, and ductile thickening of the crust are restricted to the NE parts of the belt, and the deformation is limited mainly to folding and thrusting of the sedimentary cover above a Triassic basal detachment there in the SW parts.