Strike-slip faulting in the central part of the Sanandaj-Sirjan Zone, Zagros Orogen, Iran

Abstract

The Sanandaj-Sirjan Zone (SSZ) is one of the main basement tectonic blocks located close to the northeastern margin of the Zagros Orogenic Belt. New observations in the central part of the zone indicate that the fault pattern is dominated by NW-trending longitudinal faults. The components of movement on the fault planes are interpreted as dextral oblique thrusting and dextral strike-slip. The identified structures along the faults were associated with the strike-slip faults (e.g., Hasan-Robat and Najafabad dextral restraining stepovers) and rotated tectonic blocks (arranged in a ‘domino’ configuration) near to the Foladshahr and Kolah-Ghazi mountains. Along the longitudinal faults, the dextral offsets of the rock units, streams, alluvial deposits and rivers were measured. The dextral offset values range from 2.4 to 2.7 km, while the estimated offsets based on the geomorphological features are between 50 and 61 m for streams, up to approximately ∼50 m for alluvial deposits and up to 2.2 km for rivers. The dextral strike-slip component on the fault planes occurs along the northern and southern margins of the SSZ, as well as directly within the zone, west and east of the study area. The evidence for strike-slip faulting in the internal part of the zone suggests that the central part of the SSZ probably was horizontally sheared in a manner consistent with a simple shear ‘card-deck model’.