Convergence history across Zagros (Iran): constraints from collisional and earlier deformation

Abstract

The Zagros orogen provides a unique opportunity within the Alpine system to evaluate the interplay between a young Tertiary collision and earlier subduction/obduction processes. Within the Crush zone and the Sanandaj–Sirjan (internal) zone separating the Zagros Fold belt from Central Iran, we document several major tectonic events taking place at the end of the Cretaceous, of the Eocene and from the Mio–Pliocene onwards (ca. <20–15 Ma). Contrary to recent interpretations, our data (cross-sections and description of the overall deformation style) strongly suggest that the Main Zagros Thrust (MZT) is deeply rooted, possibly to Moho depths, and that the suture zone effectively runs along the MZT. Field observations show that the final resorption of the oceanic domain took place slightly after 35 Ma and that collision must have started before ca. 23–25 Ma in northern Zagros. The shortening rate across the Crush zone since the Mid-Miocene (20–15 Ma) is estimated at a minimum 3–4 mm/year. Shear movements in the Crush zone during the Eocene–Oligocene period and extensional/strike-slip movements in the internal zones during the late Cretaceous point to an oblique setting early in the convergence history. A geotectonic scenario for convergence from the time of obduction to the present is finally proposed.