First‐order control of syntectonic sedimentation on crustal‐scale structure of mountain belts

Abstract

The first-order characteristics of collisional mountain belts and the potential feedback with surface processes are predicted by critical taper theory. While the feedback between erosion and mountain belt structure has been fairly extensively studied, less attention has been given to the potential role of synorogenic deposition. For thin-skinned fold-and-thrust belts, recent studies indicate a strong control of syntectonic deposition on structure, as sedimentation tends to stabilize the thin-skinned wedge. However, the factors controlling basement deformation below fold-and-thrust belts, as evident, for example, in the Zagros Mountains or in the Swiss Alps, remain largely unknown. Previous work has suggested that such variations in orogenic structure may be explained by the thermotectonic "age" of the deforming lithosphere and hence its rheology. Here we demonstrate that sediment loading of the foreland basin area provides an additional control and may explain the variable basement involvement in orogenic belts. When examining the role of sedimentation, we identify two end-members: (1) sediment-starved orogenic systems with thick-skinned basement deformation in an axial orogenic core and thin-skinned deformation in the bordering forelands and (2) sediment-loaded orogens with thick packages of synorogenic deposits, derived from the axial basement zone, deposited on the surrounding foreland fold-and-thrust belts, and characterized by basement deformation below the foreland. Using high-resolution thermomechanical models, we demonstrate a strong feedback between deposition and crustal-scale thick-skinned deformation. Our results show that the loading effects of syntectonic sediments lead to long crustal-scale thrust sheets beneath the orogenic foreland and explain the contrasting characteristics of sediment-starved and sediment-loaded orogens, showing for the first time how both thin-and thick-skinned crustal deformations are linked to sediment deposition in these orogenic systems. We show that the observed model behavior is consistent with observations from a number of natural orogenic systems.

Insights Into the Crustal‐Scale Dynamics of a Doubly Vergent Orogen From a Quantitative Analysis of Its Forelands: A Case Study of the Eastern Pyrenees

“…As described in section 6.1, Late Cretaceous shortening was distributed across both the Iberian and European rifted margins, before the convergent system evolved into an asymmetrical, pro-wedge-dominant orogen (Figures 8b and 8d). Models of doubly vergent orogens with distinct lower and upper plates typically show Tectonics 10.1002/2017TC004731 a pro-wedge-dominant shortening distribution (Beaumont et al, 2000;Cruz et al, 2008;Duerto & McClay, 2009;Erdős et al, 2014Erdős et al, , 2015Hoth et al, 2007;Hardy et al, 2009;Jammes & Huismans, 2012;Jammes, Huismans, & Muñoz, 2014;Sinclair et al, 2005). However, at the onset of Pyrenean convergence, no such distinction can be made.…”

“…It is common in foreland basin modeling and fold-and-thrust belt studies to analyze only one side of a doubly vergent orogen (e.g., Decarlis et al, 2014;Ershov et al, 2003;Fillon et al, 2013). However, several studies, mainly based on mechanical modeling, suggest that pro-and retro-wedges interact in accommodating plate convergence (Erdős et al, 2015;Hoth et al, 2007Hoth et al, , 2008Sinclair et al, 2005;Willett et al, 1993). Correlating the behavior of the two wedges in doubly vergent orogens can therefore provide important insight into orogen dynamics.…”

Salt décollement and rift inheritance controls on crustal deformation in orogens

“…To show the influence of décollement rheology and rift inheritance, supplementary models S1 and S2 use a weak frictional décollement that is at least 10 times stronger than the décollement in Model 1 and no rift inheritance, respectively. The supplementary models are similar to earlier work (Erdős et al, ; Erdős et al, ) and are included for comparison with Model 1 and for new quantitative analysis of the shortening distribution between pro‐ and retro‐wedges.…”

“…Here, we build on previous work (Erdős et al, ; Erdős, Huismans, & van der Beek, ) that investigates the role of rift inheritance and surface processes using lithosphere scale high‐resolution 2D thermo‐mechanical models. Critically, we use a highly mobile cover (viscous salt décollement layer) instead of the moderately mobile cover (frictional‐plastic décollement layer) used by Erdős et al (), Erdős et al (). To investigate the combined effect of rift inheritance and a highly mobile cover we present a novel measurement of the shortening distribution between the pro‐ and retro‐wedges through time (Data S1).…”

Sedimentation and viscosity controls on forearc highs

“…Surface processes and orogen rheology strongly influence the first-order evolution of accreting orogenic wedges. Syntectonic erosion (e.g., Koons, 1990;Willett, 1999) and sedimentation (e.g., Willett & Schlunegger, 2010;Fillon et al, 2013;Erdős et al, 2015) affect the distribution of strain and the deformation patterns within the wedge. Higher ductility results in structures otherwise absent, like backward thrusting sequences (Smit et al, 2003).…”