Geometric and kinematic analyses of thick-skinned in the Zagros orogenic belt

The study area is located in the Gushti area between 30º 40' to 31º N Latitude and 53º to 53º 20' E Longitude. Mylonitic nappes and shear zones in the area are a portion of internal zone of the Zagros orogenic belt. They consist mainly of ductile deformation and basement involvement structures which is referred as thick-skinned tectonics. Geometrically, most structures include a NW-SE trending and hinterland dipping thrusts. Kinematics indicators are well-developed in this area. Study of porphyroclasts as well as quartz c-axis measurments indicate dextral sense of shearing. The quartz c-axes exhibit strong lattice preferred orientation (LPO) patterns. The calculated kinematic vorticity number (Wk) is 0.77±0.14, which indicates 56% simple shear and 44% pure shear components. RGN method measurements also show similar results. The measured LPO patterns of hornblendes display asymmetric patterns with respect to shear band foliation which exhibit dextral sense of shear. These results suggest that geometric and kinematic properties of the thick-skinned of the Zagros orogenic belt correspond to a fold and thrust belt with involved-basement thrusts which indicate ramp-dominated tectonics.