Geometry and Kinematic Analysis of Laniz Structural Sub-zone; Evidence for Structural Evolution of South Central Alborz Range

Laniz structural sub-zone, located between Ahar-Maygoon faults in north and Imamzad-e-Davood fault in south, is one of the structural sub-zones in the south of Central Alborz range. In this paper, an intial model is presented on structural evolution of the Laniz sub-zone as one of the south Central Alborz range sub-zones. This model is based on geometry, kinematics, and strain analysis of the structures. The model can also be used as a refrence frame to interpret structural evolution of the south Central Alborz range. Field mapping accompanied by structual interpretation of the study area shows that thrust faults with minor strike component that dip towards north and south, are the main structures that control deformation in the sub-zone. The geometry of these thrust faults is similar to the geometry of Pop-up structures in which the older rocks are exposed and well developed in all structural sub-zones of the range. Hangingwall antiforms and footwall synforms accompany all these thrust faults. These folds are asymmetric and their geometric and kinematic analysis show that they were developed by propagation of thrust faults. Therefore, they were classified as fault propagation folds. These thrust faults were disrupted and translated by almost north-south trending transverse faults with greater strike slip component. Furthermore, these faults that also caused passive rotation of the thrust-related folds are interpreted as the result of interaction between Alborz range and Caspian Sea ocanic floor basin in Late Tertiary. This caused compressional and thrust tectonics to be substituted by transpressional tectonic regim in the south Central Alborz range. The very low values of measured strain on samples along the fault zones indicate that this tectonic regim is of the thin-skinned one.