Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Impact of an interbedded viscous décollement on the structural and kinematic coupling in fold-and-thrust belts: Insights from analogue modeling Sandra Borderie ⁎ , Fabien Graveleau, César Witt, Bruno C. Vendeville Univ. Lille, CNRS, Univ. Littoral Côte d'Opale, UMR 8187, LOG, Laboratoire d'Océanologie et de Géosciences, F 59 000 Lille, France ARTICLE INFO Keywords: Compressional tectonic wedge Experimental modeling Salt décollement Foreland Kuqa Basin Salt range ABSTRACT Fold-and-thrust belts (FTBs) can be segmented both across and along strike because of various factors including tectonic and stratigraphic inheritance. In this study, we investigated along/across-strike structural interactions in a FTB propagating toward a foreland which displays contrasted lithological sequences. A set of analogue models was performed in a compressional box where a single viscous level of varying width was interbedded within a frictional series. The tectonic interaction between the viscous and the frictional provinces was tested both along and across strike. Results indicate that a frictional province influences the along-strike tectonic evolution of an adjacent viscous province. This influence decreases when the width of the viscous province increases. The frictional provinces control the taper, structural style, obliquity of the structures' trend and ki- nematics of the shallow deformation front of the viscous province. Results evidence how far a frictional province can impact the deformation of an adjacent viscous province. For frictional-viscous wedges, it appears that the critical taper theory, which is generally applied in 2-D, should be likely considered in terms of 3-D. Moreover, the kinematics of the deep deformation front shows mutual influences between the adjacent viscous and fric- tional provinces. Experimental results are compared to natural examples in the Kuqa Basin (Southern Tian Shan, China) and the Salt Range (Pakistan), and give an insight to a better understanding of the dynamics of fold-and-thrust belts bearing a viscous décollement, such as salt. 1. Introduction The influence of décollement strength on the dynamics of accre- tionary systems has been largely investigated through experimental and numerical modeling (Buiter, 2012; Graveleau et al., 2012). Several studies investigated the influence of low or high strength basal déc- ollement (e.g. Contardo et al., 2011; Costa and Vendeville, 2002; Nilfouroushan et al., 2012; Ruh et al., 2012) and the effect of an in- terbedded low-strength décollement (Ahmad et al., 2014; Ballard et al., 1987; Corrado et al., 1998; Couzens-Schultz et al., 2003; Guillier et al., 1995; Kukowski et al., 2002; Letouzey et al., 1995; Massoli et al., 2006; Santolaria et al., 2015; Verschuren et al., 1996; Wang et al., 2013). In the commonly accepted critical taper theory setting (Dahlen, 1990; Davis et al., 1983), general results indicate that the surface slope of the wedge is steeper for a strong basal mechanical coupling than for a weaker one. Deformation propagates also typically toward the foreland for purely frictional décollement (with the so-called “in sequence” mode), whereas deformation alternates back and forth between the hinterland and the foreland if the basal décollement is viscous (“out-of- sequence mode”). The wedges grow also rather by frontal accretion of successive box folds at a low basal strength whereas it grows by im- brication of long thrust slices at high basal strength. The question of structure vergence across accretionary systems remains still not fully understood. Many works in the field and with modeling approaches have addressed the topic (e.g. Greenhalgh et al., 2015; Gutscher et al., 2001; Zhou et al., 2015), but the control exerted by décollement strength, 3-D local stresses and rotation of structures, among others, is still a subject of recurrent investigations in fold-and-thrust belts (FTB). The dynamics of triangular zones, that are wedge-shaped bodies bounded by opposite verging thrusts (Banks and Warburton, 1986; Jones, 1996) remains also to be elucidated. In nature, the strength of the detachment layer may vary along and across strike because of changes in depositional environments in the foreland (Morley, 1987). This implies variations in the mechanical stratigraphy of the foreland, and therefore variations in the structural style when the deformation front reaches this area. Several studies have analyzed the dynamics of a wedge advancing toward provinces dis- playing across-strike variations in the basal detachment strength. For http://dx.doi.org/10.1016/j.tecto.2017.10.019 Received 7 September 2016; Received in revised form 8 September 2017; Accepted 19 October 2017 ⁎ Corresponding author. E-mail address: sandra.borderie@univ-lille1.fr (S. Borderie). Tectonophysics 722 (2018) 118–137 0040-1951/ © 2017 Elsevier B.V. All rights reserved. MARK