Structural characteristics of the transitional zone from internal to external parts of the Zagros orogen, Iran

Mapping and detail field investigations, integrated with geophysical data in Bakhtyari area across the transitional zone of the Zagros orogen shows a number of SW-verging thrust sheets. Kinematic analysis of these sheets using deformed structures at the basal thrust zone as well as geophysical data from basement top allow us to recognize internal and external thrust sheets. The former show duplex thrust system with ductile–brittle deformation conditions while the latter have imbricate fan thrust system with brittle deformation condition only. The internal thrust sheets, along which the basement is also involved, converge downward to form a crustal scale ductile thrust, referred here as the root zone to the Zagros orogen. This root zone proposed as a suture to the Zagros orogen and the boundary between the Afro-Arabian Plate and the Eurasia Plate. The time for initiation of thrusting based on the Late Miocene age of syn-tectonic Bakhtyari Conglomerate is compatible with the time of continent–continent collision between the Afro-Arabian Plate and the Eurasia Plate determined by the plate reconstructions.