Abstract
Anisotropy of magnetic susceptibility can provide insights into strain distribution in models simulating fold-and-thrust belts. Models with layers of sand and magnetite mixture shortened above adjacent décollements with high and low friction, are used to study the effect of décollement friction on the magnetic fabric. Above high-friction décollement, an imbricate stack produced a ‘tectonic’ fabric with magnetic foliation parallel to thrusts. In contrast, above the low-friction décollement deformation propagated farther into the foreland, and deformation intensity is gradual from the foreland to the hinterland by defining a transition zone in between. In this zone, magnetic lineation rotated parallel to the deformation front, whereas in the hinterland the principal axes do not show a preferred orientation due to different deformation mechanisms between “thrust-affected” and “penetrative-strain affected” area. Above both décollement types, the principal axes of susceptibility developed tighter clustering with depth. Along the boundary between the two décollements, a deflection zone formed where rotation of surface markers and magnetic fabric reflect the transition between structures formed above the different décollements. Through quantifying magnetic fabric, this study reemphasises the clear link between décollement friction, strain distribution and magnitude in fold-and-thrust belts.
Highlights
(TZ), hinterland above low-friction decollement (HLF), deflection zone (DZ) with strike-slip fault that developed due to different deformation propagation above each decollement, and a boundary zone in the hin terland (HBZ) where deformation above each different decollement interfere without forming a deflection zone
Results of a shortened sandbox model show that decollement friction has a significant impact on the development of magnetic fabric in a foldand-thrust belt
The anisotropy of magnetic susceptibility (AMS) depicts the difference in deformation above each decollement, where the wedge geometry, taper, fault vergence, and deformation propagation vary with decollement friction (Fig. 7)
Summary
Many models have addressed the influence of basal friction on the geometric, kinematic and dynamic evolution of fold-and-thrust belts (FTB) (e.g. Davis et al, 1983; Dahlen et al, 1984; Colletta et al, 1991; Huiqi et al, 1992; Mulugeta and Koyi, 1992; Willet, 1992; Gutscher et al, 1996; Cotton and Koyi, 2000; Koyi et al, 2000; Agarwal and Agrawal, 2002; Costa and Vendeville, 2002; Bahroudi and Koyi, 2003; Koyi and Vendeville, 2003; Koyi and Cotton, 2004; Nilforoushan and Koyi, 2007; Nilforoushan et al, 2008; Vidal-Royo et al, 2009). Davis et al, 1983; Dahlen et al, 1984; Colletta et al, 1991; Huiqi et al, 1992; Mulugeta and Koyi, 1992; Willet, 1992; Gutscher et al, 1996; Cotton and Koyi, 2000; Koyi et al, 2000; Agarwal and Agrawal, 2002; Costa and Vendeville, 2002; Bahroudi and Koyi, 2003; Koyi and Vendeville, 2003; Koyi and Cotton, 2004; Nilforoushan and Koyi, 2007; Nilforoushan et al, 2008; Vidal-Royo et al, 2009) These studies have shown that the structural style of a FTB depends on the decollement friction. Cotton and Koyi (2000) showed that a deflection zone forms in cover layers at the boundary between adjacent decollements of contrasting low- and high-friction Applying their results to the salt range in Pakistan, Cotton and Koyi (2000) concluded that the structures that develop in such deflection zones may trend parallel to the shortening direction. Taking sections during subsequent stages of deformation provides further information on internal deformation across the model and displays the 4D evolution of the model (Colletta et al, 1991; Mulugeta and Koyi, 1992)
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