Ravoshk fan-shaped structure in the southeast of Qayen: origin and tectonic implication

Near the northern boundary of the Sistan Suture Zone to the Lut block, the Upper Cretaceous-Paleocene turbiditic unit of the Ratuk complex constructs a curved-shape structure, with an NW–trending convexity. This curved structure is located 20 kilometers to Qayen, we call it the "Ravoshk fan-shaped structure". This structure contains different structures: thrust faults in the north and north-west, following the general outer-arc strike of the Ravoshk structure; and the dextral strike-slip fault in the north and the sinistral strike-slip fault in the southeast of structure. Generally, two groups of folds gave a fan-shaped appearance to the Ravoshk structure. The first group contains close, cylindrical fold parallel to the outer-arc, while the second group composed of radial folds, which are approximately conical and have an NW-trending vertex. This later group reveals that a shortening event happened at the core of the structure. However, the outer part of the fan is remarked by conjugate normal faults, related to a tangential longitudinal strain. Parallel folds are formed as a result of the perpendicular-layer shortening and displacement of the upper Cretaceous-Paleocene turbiditic unit on an NW-dipping thrust surface. This followed by a vertical axis curving caused by layer-parallel shortening during the late Paleogene when the conical folding developed. Ravoshk structure is the trace of an NW-plunged, large conical fold which in map view is similar to the cross-section of a fan-shaped fold. The origin of this folding is probably related to a large-scale buckling at the boundary of the two mentioned tectonic terranes.