Structural Analysis of the Bala Rud Fault and the Investigation of its Effect on the Deformation and Structural Evolution of the Bala Rud, Qaleh Nar, Lab-e Safid and Kabud Anticlines

Dezful Embayment is located in the Zagros foreland folded belt. The structural style of deformation differs in different parts of the Dezful Embayment. In this research, the role of the Bala Rud basement fault as a pre-existing structure and the existence of multiple deʹcollement horizons on the deformation style of the Dezful Embayment have been investigated. Investigation of the effects of surficial effects of the Bala Rud fault is carried out using different remote sensing methods. In order to confirm the presence of this basement fault, aeromagnetic data and depth to basement map has been analyzed. For the correlation, between surficial deformation and depth information of the Bala Rud fault activity is constructed based on the analog modeling. Interpretation of seismic profiles, balanced and restored cross sections are used to study the structural style of subsurface anticlines in north of the Dezful Embayment. The Bala Rud, Qale Nar, Lab-e-Safid and Kabood subsurface anticlines in this area are situated between two décollement horizons. Gachsaran Formation is the upper deʹcollement horizon. The middle décollement horizons are Garau and Dashtak Formations which include incompetent shale sediments and evaporate units, respectively. The anticlines geometry varies horizontally and vertically. The active processes in the evolution of these anticlines during the folding are limb rotation and hinge migration. The higher shortening rate is associated with higher structural relief. These anticlines formed as detachment fold and then converted to fault propagation and fault bend folds during their evolution. These results indicate that the geometry of the Bala Rud basement fault is one of the important factors in which controlling deformation in the region. This fault, although not fully penetrated the sedimentary cover on top of the basal décollement horizon but it also plays an important role in localization of the deformation which occurred in the sedimentary sequence. Presence of a basal décollement horizon between the basement and the overlay sedimentary sequence had been separated the deformation geometry in the basement and sedimentary sequence on top. The rotation of the subsurface anticlines axis just south of the Bala Rud fault is due to increase in compression in this region following performance of the Bala Rud fault in the basement. Therefore, the Bala Rud obligue ramp, middle and basal décollement horizons are the most important controlling factors in deformation of this region.