General shear characteristics of Zagros folded belt and Zagros fold-and-thrust belt, Shiraz area, Iran

The Zagros orogen is comprised of major sub-parallel tectonostratigraphic domains, from SW to NE, Zagros Folded Belt, Zagros Fold-and-Thrust Belt, Zagros Thrust System, Zagros suture zone, Zagros Fold-and-Thrust Belt, Sanandaj-Sirjan HPLT/ HT-LP paired metamorphic belts, Urumieh-Dokhtar magmatic belt. Many authors reported pure shear as buckle folding in the Zagros folded belt (formerly named the Simply Folded Belt). Vorticity analysis and field observation in a study area in boundary of Zagros folded belt and Zagros foreland foldand- thrust belt confirms contributions of both simple and pure shear deformation components. In other words, the deformation regime in the Zagros folded belt and the Zagros Fold-and-Thrust Belt is sub simple shear or general shear with differen percentages of the simple shear component. This reveal an increase of non-coaxiality from Zagros folded belt to Zagros Fold-and-Thrust Belt. This trend emphasizes the role of the Zagros Thrust System and the High Zagros Fault in the deformation of Zagros orogenic belt. Several quantitative researches have shown that in natural shear zones, an increasing in simple shearing during the final increment of the ductile deformation implies an accelerating flow path. Based on this ideas, we suggest that thrusting along the Zagros Thrust System and High Zagros Fault as shear zones may also have involved such a non- steady state deformation path. At last Simply Folded Belt and the “High Zagros” name is not appropriate names for the SW of the Zagros orogen. So Zagros folded belt and Zagros fold and thrust belt are proposed that are more appropriate nowadays than the previous names.