Numerical investigation of deformation mechanics in fold‐and‐thrust belts: Influence of rheology of single and multiple décollements

Abstract

[1] Thin-skinned fold-and-thrust belts related to convergence tectonics develop by scraping off a rock sequence along a weaker basal décollement often formed by water-saturated shale layers or low-viscosity salt horizons. A two-dimensional finite element model with a viscoelastoplastic rheology is used to investigate the structural evolution of fold-and-thrust belts overlying different types of décollements. In addition, the influence of multiple weak layers in the stratigraphic column is studied. Model shale décollements are frictional, with lower friction angles as the cover sequence. Model salt layers behave linear viscous, due to a lower viscosity as the cover sequence, or with a power law rheology. Single viscous décollement simulations have been compared to an analytical solution concerning faulting versus folding. Results show that fold-and-thrust belts with a single frictional basal décollement generate thrust systems ramping from the décollement to the surface. Spacing between thrust ramps depends on the thickness of the cover sequence. The structural evolution of simulations with an additional low-frictional layer depends on the strength relationship between the basal and the intersequential décollement. Tectonic underplating and antiformal stacking occur if the within-sequence décollement is weaker. In the frontal part of models, deformation is restricted to the upper part and imbrication occurs with a wavelength depending on the depth of the intermediate weak layer. "Salt" décollement with a viscosity of 10 18 Pa⋅s leads to isolated box folds (detachment folds). Multiple salt layers (10 18 Pa⋅s) result in long-wavelength folding. Our results for both frictional and viscous décollements are in bulk agreement with the Mohr-Coulomb type, critical wedge theory.Citation: Ruh, J. B., B. J. P. Kaus, and J.-P. Burg (2012), Numerical investigation of deformation mechanics in fold-and-thrust belts: Influence of rheology of single and multiple décollements, Tectonics, 31, TC3005,

Effects of cohesion on the structural and mechanical evolution of fold and thrust belts and contractional wedges: Discrete element simulations

“…For the basal décollement strength and internal friction values used here, there is a clear preference for forethrusts to accommodate shortening and thickening of the wedge, although complementary conjugate back thrusts do develop, distributing deformation throughout the wedge. Back thrusting is observed in physical sandbox models as well, typically under low basal strength conditions [e.g., Cotton and Koyi , ; Cubas et al ., ], but also as more subtle, transient features in the frontal regions of the wedges as seen here [e.g., Ruh et al ., ]. An interesting feature observed in all of these simulations is the early generation of small offset back thrusts near the deformation front, typically before new forethrusts develop and accommodate most of the horizontal shortening.…”

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…Supplementary Materials: The following are available online at www.mdpi.com/2076-3263/7/3/71/s1 [311][312][313][314][315][316][317][318].…”

Orogeny

“…However, recent studies have demonstrated that the characteristics and the wavelength of folding in fold-and-thrust belts are strongly influenced by rheological parameters and 2014 mechanical isotropies of the stratigraphic pile (Yamato et al, 2011;Ruh et al, 2012). Therefore, future research will focus on mechanical reconstructions of fold-and-thrust belts (Simpson, 2009;Frehner et al, 2012;Vidal-Royo et al, 2012) including three-dimensional mechanical interaction of fold and fault growth (Schmid et al, 2008a;Grasemann and Schmalholz, 2012).…”