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

Abstract

Radiolarites have an important role in the reconstruction of the paleogeography, bathymetry and their coexistence with ophiolites gives an opportunity to determine the tectonic history of collisional zones. The radiolarite units of the southwestern Neyriz are part of the Zagros accretionary prism and positioned beneath the thick bedded carbonate sediments of Tarbur Formation. The existing various structural elements within this unit give a unique fortunate for investigation on the deformation history and studying of the kinematics of the Zagros collision zone. The numerous evidence show that this unit has experienced different deformation conditions during ongoing 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 transpressional 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 folding 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.