Writers : Ghafari Nik, Baharak; Supervisor: Dr. Mohammad Reza Qaemi
Refference : Msc.Thesis-Geological Survay of Iran-Research Institute for Earth Sciences

Abstract :

The mesoscale structures of Ahmad - Abad region include interesting pheno- mena of fault – related folding in two generations, which are basically found in calcareous-shaly unit (K1l.sh) of Lower Cretaceous. These structures are not present in other units because of their different litology. The general strike of structures (NE-SW and NW-SE) are parallel to the general trend of other structures in Khanoran region. The NE-SW structures were formed in a regional stress regime with NW-SE trend in Upper Cretaceous up to Paleocene time. The Gholeh-Sib syncline is a major structure of area composed of K1l.sh unit. With the progress of deformation, the interiayer slip surfaces were produced at low competent (shaly) parts of this unit. Splaying.
off some thrust faults from these surfaces,the first generation of fault-related folds developed with NE-SW trend. The trend of regional major stress changed from NW-SE to NE-SW after Miocene and before Pliocene. The direction of slip on the interlayer slip surfaces that were formed earlier chenged and became perpendicular to earlier one. with splaying some minor Thrust fault off these surfaces, fault-related folds with NW-SE trend were produced. The fault-related folds in these region are divided into fault-bend folds, fault-tip folds, fault-propagation folds and antiformal stacks. Fold geometry and deformation style in these folds may be favorably explained with Trishear model. There are also some map-scale folds in the study area that are not related to faulting. They are mostly exposed in the limbs of Gholeh-Sib syncline. We relate these folds to second order or S- shape folds of Ghoteh-Sib syncline. There are also aboundant normal and strike slip faults in this region, however they did not have any important role in deformation of the rock units of study area, therefore they were not studied in detail. Normal faults were developed due to local extentions after termination of regional compressional stresses. During these phases, some structural elements, such as extentional veins, joints, kink bands and feather joints were formed. They were used in interpretation of hIstbry of deformation in calcareous-shaly unit of Lower Cretaceous age.

Subject List : deformation