Slip partitioning and inclined dextral transpression along the Zagros Thrust System, Iran

Flexural duplex structures and shear zones are well developed in the Heneshk area, in southwestern Iran. The Zagros Thrust System in this area consists of eight sheets of NW-striking, NE-dipping dextral strike-slip duplexes that are linked with imbricate fans and oblique-slip thrusts. The Zagros Thrust System is a portion of the internal zone of the Zagros orogenic belt. This internal zone is characterized by penetrative plastic deformation and metamorphism. Based on the kinematic vorticity number (Wk = 0.73 ± 0.02) calculated from quartz porphyroclasts of the Goshti shear zones along the Zagros Thrust System, the estimated θ angle between the maximum instantaneous strain axis (ISA) and the transpressional zone boundary is 33°. The estimated α angle of the plate convergence or the flow apophysis of the displacement field is 25°.The presence of dominantly dextral shear sense indicators in the area is consistent with dextral inclined transpressional convergence. The mean estimated finite deformation ( W m ) value indicates relative contributions of 47% pure shear and 53% simple shear for the deformation which involved both strike-slip and oblique slip displacements. In this inclined transpression, about 40% strike-slip partitioning was required to accommodate the finite strain and re-orientation of instantaneous strain.