Folded Radiolarite Unit as a Kinematic Indicator of the Zagros Collision Processes, Southwestern Iran

Radiolarites have an important role in the reconstruction of the paleogeography, bathymetry and their coexistence with ophiolites gives an opportunity to determine the tectonic his- tory of collisional zones. The radiolarite units of the southwestern Neyriz are part of the Zagros ac- cretionary prism and positioned beneath the thick bedded carbonate sediments of Tarbur Forma- tion. The existing various structural elements within this unit give a unique fortunate for investiga- tion on the deformation history and studying of the kinematics of the Zagros collision zone. The nu- merous evidence show that this unit has experienced different deformation conditions during ongo- ing evolution, including ductile, brittle-ductile and brittle deformation conditions. The main strike of E-W for axial planes of folds, eastward trend and plunge of fold axes, boudins＇ neck axes and Type III of the fold interference patterns are indicators of formation and evolution of folds during tran- spressional deformation. Structural evolution of the study area has been affected by an NE-dipping subduction zone of Neo-Tethyan oceanic lithosphere below the Iranian microcontinents. These structural elements suggest that high mechanical anisotropy and two successive generations of fold- ing simultaneously with thrusting and extrusion of this unit had led to formation and evolution of this highly asymmetrical folded unit on top of the subducted oceanic crust.

Strain Geometry and Vorticity Analysis of the Deformed Radiolarian Rocks in the Abade-Tashk Area,the Zagros Suture Zone,Iran

Deformation in the Zagros suture zone is a result of the oblique collision of the AfroArabian continent with the Central Iranian microcontinents.Various types of folding and faulting are characteristic features of the study area and indicate the performance of a high strain tectonic regime in this region.To distinguish deformation geometry during the collisional events,strain measurements have been carried out,using the R_(f)/φ method on deformed radiolarian microfossils,in the Zagros suture zone.Based on the results,the strain ellipsoid shape is in the range of general flattening to plane strain(K=0.16 – 1.12).Measured mean kinematic vorticity number(W_(m)) in the deformed radiolarian rocks ranges between 0.50 and 0.87,which implies that exhumation of the Abade-Tashk area was facilitated by a general shear flow(35%<simple shear<65% and 45%<pure shear<65%).Kinematic vorticity numbers,the amounts of Octahedral shear strain,the ellipsoid eccentricity,and strain ratios systematically increasing towards the thrust fault.The study of deformation in the study area shows that the Zagros suture zone can be considered as a transpressional zone.