CONSTRAINING OF STRAIN ELLIPSOID SHAPE FROM SECTIONAL DATA IN THE AU BEARING SHEAR ZONE WEST OF IRAN

Ductile shear zone recorded valuable data about the progressive deformation and geodynamic setting of the earth crust. Analysis of the strain ratio on the deformed quartz grains in the samples of the Zagros orogenic shear zone indicated generally most of the strain ellipsoids shape are prolate and developed under constructional strain regime. Principal axes of the strain ellipticity ratio varied in the range between 2.04 to 3.12, shear strain magnitude analysis indicated s, are between 0.6 to 1.3. Strain ellipsoid shape also revealed the propagation of the shear zone could not be coeval with the continental collision because in the collision region expected the ellipsoid shape to be oblate. Flattening strain regime in the Zagros Orogeny contemporaneous with the collisional event (D1 phase) and widespread in the Sanandaj-Sirjan Metamorphic Zone. Constructional conditions and prolate strain ellipsoid could be related to the post-collisional deformation phase (D2 phase). In this event stretching and shearing localized in the ductile shear zone and transtension structures superimposed on the former transpression structures. The deformation followed by third phase and brittle event (D3 phase) and caused to the propagation of veins. These veins somewhere cut the foliation and in the other place are parallel to foliation plane.