oa 4-D Modeling of interactions between salt ridges, salt diapirs and folding: A new interpretation of the southern Zagros and offshore Iran structures

The salt diapirs of the southern Zagros and offshore Iran, have been revisited in order to discuss their relationships with the geodynamic history. Field and seismic studies show that nearly all the diapirs of the studied area developed before the Zagros folding, either as emergent diapirs forming islands in the Neogene Sea or as buried domes formed at least in late Palaeozoic. Salt-cored detachment folds and thrusts developed in the Zagros Fold-Thrust Belt during the Neogene, triggering the reactivation of pre-existing domes. Analogue modelling has been performed to investigate the parameters controlling salt diapirism, and the role of existing domes and salt ridges on Zagros folding. The models demonstrated that the main parameter, which controlled the diapirbuilding<br>phase, is the strength of the overburden (or roof thickness). When thick roofs are too strong to be pierced by gravitationally pressured salt, it requires regional erosion, extension or compression to reach the surface. These phenomena can trigger, accelerate, or localize the diapir growth. The consequences of theses models for the Zagros diapirism are as follows: (1) salt plugs, now at the surface, would have emerged soon after salt deposition in Cambrian or during an Ordovician tectonic phase, and remained at or near the surface while sediments accumulated around them; (2) the buried domes observed onshore and offshore had a thick roof that was too strong to be pierced by gravitationally pressured salt alone; and (3) various Palaeozoic ridge and diapir patterns can explain present-day salt extrusions and fold patterns, with or without basement faults reactivation.