History of faulting on the Doruneh Fault System: implications for the kinematic changes of the Central Iranian Microplate

The Doruneh Fault System is one of the major transcurrent faults in central Asia, extending similar to 900 km from western Afghanistan into West-Central Iran. The left-lateral Doruneh Fault System is also a key structure in the Arabia-Eurasia collisional zone, bounding the northern margin of the independent Central Iranian Microplate. The Doruneh Fault System exhibits a curved geometry, and is divided here into three segments: Eastern, Central and Western. We present the results of geological, structural and geomorphic studies into the nature of recent activity along the Doruneh Fault System segments. A surprising observation is that small, relatively young drainage systems often show recent systematic left-lateral displacement across the fault, whereas large rivers indicate a former more complex right-lateral history. Furthermore, the existence of right-lateral offsets of pre-Pliocene rocks and S-C fabrics confirm this earlier phase of right-lateral movement on the fault. We suggest that the early right-lateral kinematics resulted from an earlier NW-SE-directed regional shortening, associated with the anticlockwise rotation of the Central Iranian Microplate. The shortening is characterized by the NE-SW-striking en cchelon folds within the fault slivers, the right-lateral Taknar imbricate fan and the superimposed folding exposed north of Kashmar. Thus, assuming an initiation age of Eocene (55.8 Ma) for the fault, we estimate a former right-lateral slip rate of about 5.2-5.5 mm yr(-1), which accompanied the 35 degrees. anticlockwise rotation of the Central Iranian Microplate. According to our study, the youngest units exhibiting right-lateral displacement are Middle Miocene in age, suggesting a post-Middle Miocene timing for the onset of slip-sense inversion.