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

Abstract

Deformation in the Zagros suture zone is a result of the oblique collision of the Afro-Arabian 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.

Keywords

transpression / Zagros suture zone / deformed radiolarian microfossils / vorticity analysis / Abade-Tashk area / tectonics

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