Propertional shortening mechanism in the Eocene Northwestern structural Arc of Birjand, Eastern Iran

In Eastern Iran, the Eocene platform deposits of northwest of Birjand, are a suitable case; because a thin thrust sheet of Eocene carbonate have had the possibility to slide and fold upon an upper cretaceous plastic footwall. Moreover, this carbonate sheet entirely covered the structural arc, conduct us to recognize the origin of the bending. Achieving to this goal, we passed the structural arc along the six cross sections; four sections along radial trends and two transversal sections parallel to the inflection line. In these measurements, folds and thrust faults were defined as far as possible. The cross sections have been restored by the "Move Softwear". The amount of shortening along the radial sections were measured respectively from the east to the west are the 30-40% along A, 25-35% along B, 35-45% along C, and 15-25% along D; and along the transversal section are respectively from the south to the north about the 35-55% along E and 25-35% along F. The shortening amount in the platform carbonate at two-facing ends of the structural arc as well as the one along the inflection line are the greatest. The pattern of shortening in the arc seems to follow a buckle folding mechanism.