Slab Rollback Orogeny Model for the Evolution of the Central Alps: Seismo-Thermo-Mechanical Test

Abstract

The role of mantle-lithosphere interactions in shaping mountain belts has long been debated. Several conceptual models implicate a key role for horizontal kinematic forces in sustaining mountain building processes. For the central European Alps, however, recent stratigraphic, palaeo-altimetry and lithosphere structural evidence suggest that dynamic vertical forces—provided by a Slab Rollback Orogeny (SRO) model—are the primary determinant of the latest construction of thick nappe successions, the large-scale tectonic evolution, and the present-day seismicity pattern. In this study we investigate this hypothesis by performing 2-D, high-resolution, rheologically consistent, visco-elasto-plastic seismo-thermo-mechanical numerical modeling, which simulates both tectonic and seismic processes in a subduction and continental collision setting. Our numerical experiments reproduce the self-driven stages of oceanic subduction, continent-continent collision, and spontaneous slab breakoff. The subsequent evolution of the orogen shows how slow, but persistent, flexural bending of post-collisional residual slab and crustal delamination control the latest evolution of the orogen. Bending-related slab suction leads to the coeval development of nappe stacking of the buoyant crustal root, widening of the orogen, and a distinctive seismicity pattern that implies the occurrence of extensional forces at work in the orogen and beneath the foreland basin. Our results thus suggest that a self-sustaining rollback mechanism is capable of explaining the post-collisional evolution of the Central Alps, including the construction of thick sedimentary successions in the Molasse foreland basin and the most recent tectonic deformation of the Jura fold-and-thrust belt.