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

Abstract

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 décollement 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 décollement 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.

Paleogeothermal Gradients Across an Inverted Hyperextended Rift System: Example of the Mauléon Fossil Rift (Western Pyrenees)

“…To simulate this pulse, a Gaussian‐type horizontal profile is imposed at a depth of 30 km in the model: where Q m is the mantle heat flow, Q m 0 is its maximum value at the model center (horizontal distance x = 0), and λ is a characteristic width of the thermal pulse (the half width of the gaussian curve). Previous thermal models (Duretz et al, 2019; Jourdon et al, 2019, 2020) used different initial thermal regimes resulting in a thermal anomaly that is 50–100 km wide at Moho depth. Accounting for the gaussian shape of Q m, we tested two values of λ, 25 and 75 km.…”

“…The different thermal responses on the opposite sides of the pop-up structure can be linked to their tectonic reactivation style. Indeed, exhumation is limited in the northern retro-wedge, which was affected by thinskinned deformation on an Upper Triassic salt décollement, and significantly greater in the southern prowedge, which underwent thick-skinned deformation (Figure 12a; Jourdon et al, 2019Jourdon et al, , 2020Saspiturry, Allanic, et al, 2020). The post thrusting thermal structure along the Lakhoura thrust system was preserved due to sequential activation of thrusting southward and below the Lakhoura thrust system.…”

Basement-involved thrusting, salt migration and intramontane conglomerates: a case from the Southern Pyrenees

“…The frontal part of the antiformal stack, detached by erosion from its root to the north, consists of forelanddipping thrusts and related downward-facing folds referred to as the Nogueres têtes plongeantes (Séguret, 1972). Recent numerical modelling studies have explored the role of the Triassic evaporites in crustal-scale orogenic inversion, which are key in enabling gliding, stacking and rotation of the duplex thrusts (Grool et al, 2019;Jourdon et al, 2020). In the South-Central Pyrenees, the Nogueres thrust sheet consists internally of a set of minor imbricates of Silurian and Devonian metasedimentary rocks with Permo-Triassic deposits unconformably on top (Mey, 1968;Séguret, 1972;Zwart, 1979;Muñoz, 1992;Saura and Teixell, 2006).…”

Preorogenic Folds and Syn‐Orogenic Basement Tilts in an Inverted Hyperextended Margin: The Northern Pyrenees Case Study

“…Early shortening in the Pyrenean domain (Late Cretaceous, 83 to 75-70 Ma, Mouthereau et al, 2014) was first accommodated by the closure of the exhumed mantle domain, followed by continental plate underthrusting (Gómez-Romeu et al, 2019;Jammes et al, 2009;Mouthereau et al, 2014;Teixell et al, 2016;Tugend et al, 2014Tugend et al, , 2015. Topography building and foreland flexure were limited during these first convergence stages and could be partly delayed by the presence of a thick salt layer uncoupling the cover from the deep crust and mantle lithosphere (Jourdon et al, 2020). The subsequent full collision stage (from 75-70 Ma to the early Miocene in the Central Pyrenees; Mouthereau et al, 2014; from the late to mid-Eocene in the western Pyrenees; Gómez-Romeu et al, 2019;Teixell et al, 2016) was mostly resolved through the southward thrusting of the upper Iberian crust and the subduction of the lower Iberian crust underneath the European plate (Muñoz, 1992;Teixell, 1998;Teixell et al, 2016).…”

“…Early shortening was mostly accommodated by the closure of the exhumed mantle domain (Jammes et al, 2009;Jourdon et al, 2020;Lagabrielle et al, 2010;Masini et al, 2014;Tugend et al, 2014) and the reactivation of early extensional basement faults in the southern basin margin (these extensional faults could locally be preserved, Figures 5a and 5b) as top to the south thrusts. Reactivated faults transported passively the early folded cover in the CB in their hanging wall.…”