Subduction Dynamics and Rheology Control on Forearc and Backarc Subsidence: Numerical Models and Observations from the Mediterranean

The dynamics of subduction zones is linked to the rise and demise of forearc and backarc sedimentary basins in the overriding plate. Subsidence and uplift rates of these distinct basins are controlled by variations in plate convergence and subduction velocities and determined by the rheological and thermal structure of the lithosphere. In this study we conducted a series of high-resolution 2D numerical models of oceanic subduction and subsequent continental collision. The numerical code 2DELVIS involves erosion, sedimentation, and hydration processes. The models show the evolution of wedge-top basins overlying the accretionary wedge and retro-forearc basins in the continental overriding plate, separated by a forearc high. These forearc regions are affected by repeated compression and extension phases. Higher subsidence rates are recorded in the syncline structure of the retro-forearc basin when the slab dip angle is higher and the subduction interface is stronger. This implies the importance of the slab suction force as the main forcing factor creating up to 3-4 km negative residual topographic signals. Extensional back-arc basins are either localized along inherited weak zones at large distance from the forearc region or are initiated just above the hydrated mantle wedge. Back-arc subsidence is primarily governed by crustal and lithospheric thinning controlled by slab roll-back. Our results are compared with the evolution of the Mediterranean and we classify the Western and Eastern Alboran, Paola and Tyrrhenian, Transylvanian and Pannonian Basins to be genetically similar forearc–backarc basins, respectively.