MICRO-STRUCTURAL ANALYSIS OF THE CONTINENTAL COLLISIONAL DEFORMATIONS ASSOCIATED WITH THE ZAGROS THRUST ZONE

Two kinds of geometry and deformation have been recognized along the Zagros Thrust Zone. Detailed structural mapping and miro-stuctural and palaeo-stress analysis of the Thrust Zone indicate that the Neyriz segment of the Thrust developed as a large-scale narrow dextral shear zone between two continents. It consists of upper unit of intensely deformed foliated rocks with clear S-type and C-type shear bands by low temperature brittle-ductile deformation. The upper unit grades into the lower unit with increasing grade of metamorphism up to amphibolite and granulite facies conditions at the base of the Thrust. Measurement of type I (<200° C) and type II (< 150° -300° C) of deformation twins (e-twins) in calcite of deformed porphyroclasts by U-stage suggest that active continental margin of the Iranian plate thrusted over a passive continental margin of Arabian plate trending NNW and contemporaneous with the emplacement of the Neyriz ophiolite on the continental carbonates in Upper Cretaceous. The maximum principal palaeo-stress showing NNW and NW direction and extension axes is in ESE direction. Detailed structural mapping and micro-structural analysis of Deh-Bid segment of the Zagros Thrust Zone show another type of geometry and deformation. This segment consist of compressional hinterland flexural slip duplexes. These duplexe structures developed parallel to the NW-SE fold and thrust belt with dextral shear sense. They contain incompetent dolomarble. Slate, phyllonite and mylonite. These rocks metamorphosed up to green schist facies conditions. Micro-structural analysis of mylonite quartz LPO patterns suggests that they have been deformed by non-coaxial progressive simple shear. Measurements of porphyroclasts of quartz c-axes pattern show clear internal asymmetry and external asummetry with respect to foliation indicating compressional dextral shear sense of the Zgros Thrust. Asymmetric type-I crossed girdle of the LPO patterns of quatrz c-axes developed at high strain accumulated by simple shear of low-grade metamorphic conditions.