Temporal evolution of the Darmadan salt diapir, eastern Fars region, Iran

Abstract

A wide range of diapirs crop out along the eastern Fars region. They are constituted by the Pre-Cambrian to Early Cambrian Hormuz Fm. and located in the transition from the frontal structures of the Zagros fold-and-thrust belt and the Oman Ranges. While, in different previous works about the Persian Gulf, off-shore diapirs the deformation history has been determined on the basis of subsurface data, onshore evidence for salt tectonics activity is often limited to post-Oligocene stratigraphic units and is significantly overprinted by shortening. The Darmadan diapir is one of the few salt structures where is possible to observe halokinetic sequences involving the pre-collision Mesozoic succession in the Fars region of the Zagros fold-and-thrust belt. The objective of our study was to characterize on the base of field data, the stratigraphic and structural relationships between the Hormuz salt and its overburden in order to establish its temporal evolution. The Darmadan diapir is interpreted as a salt stock connected to a salt wall structure at depth evolving to a passive diapir, at least since Late Jurassic-Early Cretaceous times. Expansional geometries toward the diapir reveal that primary welding was already occurred at the Albian time. The onset of contractional deformation in the internal part of the Zagros and Oman orogenic systems is recorded by the reactivation of the Darmadan diapir during the Late Cretaceous. The Darmadan diapir continued to be exposed during the Paleogene and was squeezed during the Neogene to recent Zagros deformation. Second-order contractional features and related growth geometries constrain the timing of the secondary welding during the early stages of the late Miocene Darmadan anticline development. The explained structure remarks that the present structural trends of the Zagros fold-and-thrust belt in the eastern Fars region are the result of the reactivation of preexistent salt structures.