The Unique Folding Style in the Zagros Simply Folded Belt, the Kuh-e Qazi Anticline, South Iran

Abstract

The study area is located in the Zagros Simply Folded Belt of Iran and in the interior Fars sub-basin (175 km from Persian Gulf). The Zagros fold-thrust belt is home to one of the largest petroleum producing reservoirs in the world. Structures in this area have complications and the study anticline has unique structures in the Fars region. In the study area, the Kuh-e Qazi anticline due to special fold style and rotation toward Northeast is the unique structure between anticlines of the Zagros belt. This anticline is fault bend fold and plunge of the anticline in eastern part rotated toward Northeast along with the Nezamabad fault trend. In this area, the Kuh-e Qazi anticline has asymmetric structures and some faults such as the Nezamabad and the Sarvestan strike slip fault effect on this anticline. The geometry of anticlines in the Zagros fold-thrust belt is affected by the type of deformation and mechanical behavior of stratigraphic units specially detachment units. The purpose of this research is to determine of folding pattern of the Kuh-e Qazi anticline and define structural features affected on them in the study area. This paper presents a part of the results of a regional study of the Fars province in the Zagros Simply Folded Belt, based on original fieldwork, satellite images, structural sections, geological maps and well data. Also, we use some software as Global Mapper and Tectonics FP for preparing some data. Based on the research, which have been done, the boundary between ductile and frictional substrates causes rotation as a result of lateral, along-strike migration of the ductile substrate. The ductile or viscose layer in the study area is Hormuz Series. Due to lack or thinning of Hormuz salt over the Gavbandi basement high and in the eastern side of the Nezamabad basement fault, causes translation of strain and anticlockwise rotation in Southeast of the Kuh-e Qazi anticline toward Northwest unlike foreland basin due to the Nezamabad fault activity. This style between all of the anticlines in the study area is unique that rotates unlike foreland basin. In addition, influence on anticlockwise rotation, extensional stress has been created and then salt dome cropping out in Southeast of the Kuh-Qazi anticline. One of the best evidence for effect of extensional stress is triangular facets in this part of the study anticline. Based on folding analysis (geometry of axial plane and fold orientation), it is clearly confirmed that the translation of strain and anticlockwise rotation in Southeast of the Kuh-e Qazi anticline toward Northwest has been formed by basement fault activity as the Nezamabad fault in the boundary between ductile and frictional substrates of the study area.