Stress states in the Zagros fold-and-thrust belt from passive margin to collisional tectonic setting

Abstract

The present-day Zagros fold-and-thrust belt of SW-Iran corresponds to the former Arabian passive continental margin of the southern Neo-Tethyan basin since the Permian–Triassic rifting, undergoing later collisional deformation in mid–late Cenozoic times. In this paper an overview of brittle tectonics and palaeostress reconstructions of the Zagros fold-and-thrust belt is presented, based on direct stress tensor inversion of fault slip data. The results indicate that, during the Neo-Tethyan oceanic opening, an extensional tectonic regime affectedthe sedimentary cover in Triassic–Jurassic times with an approximately N–S trend of the σ3 axis, oblique to the margin, which was followed by some local changes to a NE–SW trend during Jurassic–Cretaceous times. The stress state significantly changed to thrust setting, with a NE–SW trend of the σ1 axis, and a compressional tectonic regime prevailed during the continental collision and folding of the sedimentary cover in Oligocene–Miocene times. This compression was then followed by a strike-slip stress state with an approximately N–S trend of the σ1 axis, oblique to the belt, during inversion of the inherited extensional basement structures in Pliocene–Recent times. The brittle tectonic reconstructions, therefore, highlighted major changes of the stress state in conjunction with transitions between thin- and thick-skinned structures during different extensional and compressional stages of continental deformation within the oblique divergent and convergent settings, respectively.