Fracture patterns in the Zagros fold-and-thrust belt, Kurdistan Region of Iraq

This work extends the previous studies in the SE part of the Zagros fold-and-thrust belt and examines fracture systems developed in the NW Zagros, focusing on the area NE of the city of Erbil in the Kurdistan Region of Iraq. Three main fault and fracture generations have been identified during the field and remote sensing data studies in the investigated area. (1) The earliest is a penetrative sub-vertical fracture set developed in an NNE to NE direction. Since these fracture sets are cross-cut by the next generation of fractures, which are clearly connected with the folding, we conclude the age of this fractures to be pre-folding. (2) Another distinct fracture set is connected with the large-scale folding event. The fractures are oriented perpendicular to the sedimentary bedding and striking NW-SE, parallel to the major trend of the fold axes. The deformation is divided in the fold tangential extension in the outer layers of the folded sedimentary succession, forming mode I joints, tension gashes and normal faults and in the fold tangential shortening in the cores of the folds, where minor fold-and-thrust structures solve the place problems. (3) Fractures with NNE- to N-trending orientation, commonly reactivated as strike-slip faults, probably reflecting the N-S compression induced by the northward movement of the Arabian plate relative to the Eurasian Plate. Comparing the inferred palaeostrain directions with the kinematics of recent GPS measurements, we conclude that the N-S compression and the partitioning into NW-SE trending folds and NW to N trending strike-slip faults likely remained unchanged throughout the Neogene tectonic history of the investigated area.