Abstract A significant amount of the ongoing shortening between the Eurasian and Arabian plates is accommodated within the Zagros Fold‐Thrust Belt. However, the spatial and temporal distribution of active shortening within the belt, especially in its NW part, is not yet well constrained. We determined depositional ages of uplifted river terraces crossing the belt along the Greater Zab River using luminescence dating. Kinematic modeling of the fault‐related fold belt was then used to calculate long‐term slip rates during the Late Pleistocene to Holocene. Our results provide new insight into the rates of active faulting and folding in the area. The Zagros Mountain Front Fault accommodates about 1.46 ± 0.60 mm a −1 of slip, while a more external basement fault further to the SW accommodates less than 0.41 ± 0.16 mm a −1 . Horizontal slip rates related to detachment folding of two anticlines within the Zagros Foothills are 0.40 ± 0.10 and 1.24 ± 0.36 mm a −1 . Basement thrusting and thickening of the crust are restricted to the NE part of the Zagros belt. This is also reflected in the regional topography and in the distribution of uplifted terraces. In the southwestern part, the deformation is limited mainly to folding and thrusting of the sedimentary cover above a Triassic basal detachment. In the NE, deformation is associated with slip on basement thrusts. Our study sheds light on the distribution of shortening in the Zagros Mountains and helps to understand the regional tectonic system. Our results may be the foundation for a better seismic hazard assessment of the entire area.
Plain Language Summary In active mountain belts, river terraces found above the present‐day river level can be indicative of differences in uplift rates due to the thickening, faulting, and folding processes in the Earth's crust. These processes, driven by the motion of tectonic plates, are responsible for the formation of mountain belts. Here, we took sediment samples from uplifted river terraces along the Greater Zab River that crosses the Zagros Mountains in the Kurdistan Region of Iraq. We determined their deposition age using luminescence dating. From their age and elevation, we calculated uplift rates. We built a geometrical model of the fault zones in the area and determined how fast the slip occurs on these faults based on the uplift rates. Our results indicate that there were less than two millimeter per year of slip on these faults on average during the last 60 thousand years. This motion is a result of the convergence between the Arabian and Eurasian plates. With studies like this we can measure how fast fault blocks move, even if they were not associated with large earthquakes in the recent past. This approach helps to better assess the potential earthquake hazard in the area under investigation.
Key Points We estimated fault slip rates in the NW Zagros Mountains by luminescence dating of river terraces and structural modeling There is c. 1.46 mm a −1 slip on the Mountain Front Fault and c. 1.64 mm a −1 slip from detachment folding in the NE part of the Foothill Zone Crustal thickening and basement thrusting occur in the NE parts of the Foothill Zone and only cover deformation occur in the SW parts
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