Signatures of the Balarud Deep Seated Fault Zone in Khushab Anticline, SW Iran, An Integrated Study

The Khushab anticline is located in the Zagros fold-thrust belt in the Lurestan. This anticline is affected by the Balarud fault zone, which is a part of Mountain Front Fault between the Lurestan and Dezful Embayment zones. Based on the measurement of the elements of fold style, this anticline is analyzed. According to these measurements, this anticline is a noncylindrical, asymmetrical and disharmonic fold. The anticline is a z-fold and verges slightly to the southwest. The tightness and bluntness of folding suggests that fold is gentle to close and subangular respectively. Broad to wide is suggested as disccriptive term of the aspect ratio. Based on Ramsay's classification the fold is subclass 1B to 1C. The field observations, seismic profiles, cross-sections, analyses of the geometric parameters and comparison of the anticline with the fault-related fold models suggest the anticline as a detachment fold that is probably sheared by this zone. The sinistral shear of this zone, due to a system of shear fractures is discussed. These fractures (C, D, E, F, and G sets) which occur obliquely with respect to fold axis are shear fractures. Another fracture system including A and B sets are parallel and perpendicular to fold axis respectively. These fractures formed in association with folding. It seems that two phases are responsible for forming of these fractures. A and B sets were formed in first phase and associated with formation of anticline. The shear fracture system was formed in second phase and is under effect of this zone.