Numerical modelling of overriding plate deformation and slab rollback in the Western Mediterranean

Abstract

In the Western Mediterranean, rollback of the Calabrian slab resulted in a two-phase opening of the Liguro-Provençal Basin (30-16 Ma) and the Tyrrhenian Basin (9 Ma-present), with a transient quiet period in between. The cause of the discontinuous opening of these basins is not well understood, as well as the cause for the subduction to jump from the western to the eastern side of Corsica and Sardinia at the onset of extension in the Tyrrhenian Basin, leaving the Corsica/Sardinia block behind. In this study the cause of this stagnation and reactivation of rollback is investigated using 2D numerical modelling with ASPECT. To study the controlling factors on opening of the Liguro-Provençal Basin and the Tyrrhenian Basin, modelling of a central transect through the two back-arc domains is performed. The focus is on the effect of lithospheric strength, absolute plate motions and pre-existing weak zones on the evolution of overriding plate deformation. The results of the numerical models are compared to the existing geological framework. The presence and strength of weak zones seems to play a major role in the evolution of overriding plate deformation, as well as the total amount of rollback. Simulating the stagnation and reactivation of rollback has proven to be challenging in 2D due to the geometry of the narrow Calabria slab. Toroidal flow around the slab edges plays a major role on the evolution of overriding plate deformation and the rates of back-arc extension. Furthermore, the strength of the material in the weak zones is an important controlling factor for back-arc extension rates.