Topographic and Tectonic Evolution of Mountain Belts Controlled by Salt Thickness and Rift Architecture

The role of the heterogeneous rheological architecture of rifted margins in the building of mountain belts has challenged our view of how a collisional orogen formed. We show, using two-dimensional numerical experiments of collision built by the inversion of rifted margins, that a weak pre-extensional evaporitic layer delays the growth of topography and the onset of syn-orogenic sedimentary record in foreland basins. In tectonic models lacking a weak decollement layer, the orogen grows by progressive accretion of basement thrusts. With a 2-km-thick salt layer, the orogen develops an antiformal stack in the deep crust that is kinematically connected to a shallow thin-skin thrust belt in the foreland as observed in many orogens. A 5-km-thick weak layer leads to the quasi-absence of topography and widespread salt tectonics and obliterates thrusts propagation while promoting crust and mantle underthrusting. During convergence, the preservation of a marine seaway emphasizes that collision may involve a significant period of submarine continental accretion, which duration is controlled by the thickness of the weak decollement layer. From these experiments we infer that the thicker the salt layer, the longer the delay between the onset of far-field shortening and the formation of the orogen. Our study explains first-order features recognized in many orogens controlled by variable salt thickness and extension.