Determination of deformation in Bahlgerd shear zone by using geometry small-scale Structures

 
Abstract
Behlgard shear zone in eastern Iran has deformed Eocene flysch on the border with the ophiolite sequence south of Birjand. In field studies of the region, small-scale structures that are formed in brittle-ductile deformation have been considered as strain marker for assessing local deformation. For this purpose, first analytical methods based on the geometry of pattern of extension fractures, foliations, deflection of markers and initially elliptical particles have been used then these methods are compared and the limitations of their use are discussed. In the estimated values of strain using extension fractures and the curvature of foliation, the area under the distance-strain curve determines the mean shear strain (γ _mean), which should be introduced by parameter of the intensity of strain localization (I_loc). In using foliations in determining the strain, recognizing the relationship of this type of fabric with regional structures, the difference of strain patterns in shear zones with parallel and wedge-shaped walls, foliation refraction affected by the behavior of rocks, It is important and should be considered on a regional scale. Graphical methods such as Lisle (2013) due to the simplicity and calculated parameters of shear strain and volume change as compared to other methods is preferred. Methods for calculating the mean of R_f data due to the simplicity of determining the R_f parameter in elliptical markers and simple mathematical calculations to determine deformation at the regional scale. In applying different methods for determining deformation parameters, in order to control the validity of the assumptions and accurate assessment of multiple markers and strain should be used.