Mesozoic extensional brittle tectonics of the Arabian passive margin, inverted in the Zagros collision (Iran, interior Fars)

Abstract

AbstractThe present Zagros mountain belt of SW Iran is known to be the former NE Arabian passive continental margin of the southern Neo-Tethyan basin, which originated by Permian–Triassic rifting, and has a late Cenozoic collisional imbricate structure. We carried out brittle tectonic analyses of syndepositional normal fault slip data in the High Zagros Belt of the Fars Province to reconstruct the extensional deformation of the passive margin during the Mesozoic era in terms of stress tensor inversion. This reconstruction revealed two main directions of extension, developing from a north–south margin-oblique trend to a NE–SW margin-perpendicular one. Considering the basement structures and the existence of the basal Infracambrian salt detachment, we infer that a transtensional extension could have initiated two major periods of crustal stretching: a Permian–Triassic thick-skinned phase with the basement faults developing in an oblique rifting, and a Mesozoic thin-skinned phase with the sedimentary cover being affected by successive extensional structures and block tilting. This extensional tectonic history probably continued during the early Tertiary period, prior to the continental collision. Fault slip geometries and structural patterns of both the Mesozoic extension and the late Cenozoic compression indicate inversion of the inherited structures in the Zagros collision during the subsequent thin- and thick-skinned stages of crustal shortening.