Buildup of a dynamically supported orogenic plateau: Numerical modeling of the Zagros/Central Iran case study

Abstract

The Iranian plateau is a vast inland region with a smooth average elevation of c. 1.5 km formed at the rear of the Zagros orogen as a result of the Arabia-Eurasia collision (i.e., over the last 30-35 Myr). This collision zone is of particular interest due to its disputed resemblance to the faster Himalayan collision, which gave birth to the Tibetan plateau around 50 Myr ago. Recent studies have suggested that a recent (10-5 Ma) slab break-off event below Central Iran caused the formation of the Iranian plateau. Here, we test several hypotheses through large-scale (3082 × 590 km) numerical models of continental subduction models that incorporate a free upper surface erosion, rheological stratification, brittle-elastic-ductile rheologies, and metamorphic phase changes (density and physical properties) and account for the specific crustal and thermal structure of the Arabian and Iranian continental lithospheres. We test the impact of the transition from oceanic to continental subduction and the topographic consequences of the progressive slowdown of the convergence rate during continental subduction. Our results demonstrate the role of mantle flow beneath the overriding plate, initiated as an indirect consequence of slab break-off. This flow creates a dynamic topography support during continental subduction and results in delamination of the overriding plate lithospheric mantle followed by isostatic readjustment, hence of further uplift and maintenance of a plateau-like topography without significant crustal thickening. The slowdown of the convergence rate during the development of the continental subduction/collision phase largely contributes to this process by controlling the timing and depth of slab break-off.