Late Pleistocene‐Holocene Slip Rates in the Northwestern Zagros Mountains (Kurdistan Region of Iraq) Derived From Luminescence Dating of River Terraces and Structural Modeling

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 part

Fracture and bedding planes collected by compass from rock outcrops in the central German platform

A total of 1207 fracture and bedding planes including fault striations and senses of slip on the fault slickensides were collected from 93 rock outcrops in the central German platform. The data collected by geological compass, mostly from Triassic sedimentary strata, and include spatial orientation of the fracture and bedding planes in strike/dip/rake format. The data provide valuable information on relative tilt geometry between the fractures and sedimentary strata. The data, combined with additional criteria of kinematic changes, were used to reconstruct the succession of brittle deformation and states of paleostress fields during the Mesozoic and Cenozoic times. The results suggest a succession of events, which begins with a post-Triassic normal faulting regime followed by strike-slip and thrust faulting regimes, supposedly in the Late Cretaceous time, and by two younger events of normal and oblique thrust faulting regimes during the Cenozoic time

Techtonique cassante et reconstruction des paléo-contraintes dans le Zagros (paléo-marge passive et collision continentale)

Cette thèse se concentre sur l évolution tectonique cassante de la ceinture de plis et chevauchements du Zagros dans les provinces de Fars et Kermanshah de l Iran. Une reconstruction des paléo-contraintes liées à l ancienne marge passive arabe et à sa collision avec la plaque continentale iranienne est proposée. Les structures cassantes complexes, comme attesté par les analyses des rapports géométriques et chronologiques entre des failles, sédimentation tectonique et plis, révèlent de grands changements d état de contrainte. L histoire mésozoïque de la marge arable a été caractérisée par le développement de structures en extension héritées du rift au Permo-Trias et de l ouverture océanique de la Néo-Tethys. L inversion ultérieure de ces structures pendant la collision a produit une configuration structurale orogénique issue à la fois de la géométrie de marge passive et du processus de fermeture de la Néo-Tethys, caractérisée par une obduction ophiolitique discontinue et une collision continentale diachrone. La collision continentale du Cenozoïque moyen et tardif est caractérisée par des structures compressives et des décrochements révélant une réorientation des contraintes. Cette réorientation des contraintes, cohérente avec un changement graduel de la cinématique des plaques dans le Fars, ne coïncide pas avec le changement cinématique à Kermanshah, où se produit un partitionnement de la déformation à l échelle orogénique avec une convergence oblique des plaques. Le changement des contraintes a été plus probablement résulté de la dernière réorganisation de la collision, caractérisée par une augmentation du couplage des plaques.This dissertation focuses on brittle tectonic evolution of the inner zones of the Zagros fold-and-thrust belt in the Fars and Kermanshah provinces of Iran. A palaeostress reconstruction of the former Arabian passive margin and its collision with the Iranian continental plate is carried out. Complex brittle structures, as evidenced by field-based analyses on geometric and chronologic relationships between faults, syn-tectonic sediments and folds, reveal major changes in stress regimes. The Mesozoic history of Arabian margin was characterised by extensional structures inherited from the Permina-Triasic rifting and the Neo-Tethyan oceanic opening? During the continental collision, subsequent inversion of these inherited structures resulted in an orogenic structural pattern, which helped reconstructing not only the geometry of passive margin but also the Neo-Tethyan closure process, as characterised by discontinuous ophiolite obduction and diachronous continental collision. The mid-late Cenozoic continental collision is characterised by compressional and strike-slip structures, revealing stress reorientation? This stress reorientation has been fairly consistent with a gradual change in plate kinematics in Fars, but not chronogically consistent with the plate kinematic in Kermanshah, where orogenic-scale deformation partitioning occurs under an oblique plate convergence. The change in stress state has more likely been related to the late collisional plate reorganisation, as highlighted by an increase in coupling between the plates.NICE-BU Sciences (060882101) / SudocSudocFranceF

Luminescence Dating of River Terraces along the banks of the Greater Zab River in the Northwestern Zagros Mountains in Kurdistan Region of Iraq

This dataset contains details of 15 samples of the river terraces that were collected along the banks of the Greater Zab River (Kurdistan Region of Iraq) that crosses the Zagros Fold-Thrust Belt. These terraces were dated using luminescence dating including both Infrared Stimulated Luminescence (IRSL) and post-IR IRSL (pIR) to determine their depositional ages. The dataset includes details about the locations, dosimetry, and determined ages of the collected samples. The ages of the dated river terraces range from c. 165 ka to c. 6 ka. The terraces were deposited at the river level. Their present-day elevation above the river is interpreted as the amount of incision by the river that occurred in response to the uplift. The uplift rates of river terraces were integrated with kinematic modeling of the fault-related fold belt in the area 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, respectively

Late Pleistocene‐Holocene Slip Rates in the Northwestern Zagros Mountains (Kurdistan Region of Iraq) Derived From Luminescence Dating of River Terraces and Structural Modeling

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.German Academic Exchange Service (DAAD) http://dx.doi.org/10.13039/501100001655German Research Foundation (DFG) http://dx.doi.org/10.13039/50110000165

Intraplate brittle deformation and states of paleostress constrained by fault kinematics in the central German platform

The structural evolution of Central Europe reflects contrasting tectonic regimes after the Variscan orogeny during Mesozoic – Cenozoic time. The brittle deformation related to each tectonic regime is localized mainly along major fault zones, creating complex fracture patterns and kinematics through time with diverging interpretations on the number and succession of the causing events. By contrast, fracture patterns in less deformed domains often provide a pristine structural inventory. We investigate the brittle deformation of a relatively stable, wide area of the central German platform using fault-slip data to identify the regional stress fields required to satisfy the data. In a non-classical approach, and in order to avoid local stress variations and misinterpretations, the fault-slip data are scaled up throughout the study area into subsets of consistent kinematics and chronology for sedimentary cover and crystalline basement rocks. Direct stress tensor inversion was performed through an iterative refining process, and the computed stress tensors were verified using field-based observations. Criteria on relative tilt geometry and indicators of kinematic change suggest a succession of events, which begins with a post-Triassic normal faulting regime with ?3 axis trending NE-SW. The deformation then follows by strike-slip and thrust faulting regimes with a change of ?1 axis from N-S to NE-SW, supposedly in the Late Cretaceous. Two younger events are characterized by Cenozoic normal and oblique thrust faulting regimes with NW-SE-trending ?3 and ?1 axes, respectively. The fracture patterns of both the cover and basement rocks appear to record the same states of stress