Investigation of the effect of rheology on the upper plate deformation in subduction systems via numerical simulation: Insight into the Eocene Neothetys subduction in Iran

The aim of this study is to simulate stress variations and deformation of the continental plate in the subduction process. The main concept considered is that trench retreat during the subduction process can lead to the creation of an extensional stress regime in the overriding continental plate, and subsequent extension tectonics, and the thinning of the continental crust. The Iranian plate experienced distributed extension in the Eocene. One of the scenarios regarding this event considers the roll-back of the Neo-Tethys slab at that time as the cause of the extensional stress regime. Through numerical simulations to solve the conservation equations governing the flow and deformation in the crust and mantle, the role of rheology, thickness and age of the continental plate in the above-mentioned developments have been investigated. The results show that trench retreat can occur for a large range of physical parameters. Prolonged trench retreat can lead to a localized extensional tectonic regime near the edge of the continental plate above the subduction zone, 7 to 12 million years after the initiation of subduction. For a lithosphere with strong rheology, this tectonic regime results in negligible thinning, too small to be observable in the geological record. In contrast, for weaker continental plate, as well as a thin lithosphere, a wide-range of extensional deformations can occur, some of them comparable in terms of amplitude and time-scale with the events of the Eocene in central Iran.