Gravity influenced brittle‐ductile deformation and growth faulting in the lithosphere during collision: Results from laboratory experiments

Abstract

[1] Because of the competition between brittle and ductile rheologies and their interplay with tectonic and buoyancy forces, lithospheric deformation results in very contrasting styles. In continental collision, especially with unconfined boundaries, deformation can be either homogeneously distributed or localized on complex fault patterns, and different deformation modes such as contraction, extension, and strike-slip interfere. Using scaled lithospheric analog experiments made of dry sand, silicone putties, and dense honey, we investigate the mechanical parameters that control the deformation style in colliding systems, with a particular focus on the roles of buoyancy and brittle-ductile coupling. The analysis of tens of experiments shows that the principal deformation features depend on two main parameters: a brittle-to-ductile strength ratio G, which controls deformation localization at the largest scale, and a buoyancy-to-strength ratio Ar, which fixes the relative amount of contractional, extensional, and strike-slip structures. Strain localization occurs only for G larger than a critical value ($0.5), and the range of G values, over which the transition from nonlocalized to localized deformation occurs, is small. The three main deformation regimes (contraction, strike-slip, and extension), which coexist in most of the collision experiments, occur in relative proportions that depend mainly on Ar and on the nature of the boundary conditions. Citation: Schueller, S., and P. Davy (2008), Gravity influenced brittle-ductile deformation and growth faulting in the lithosphere during collision: Results from laboratory experiments,

A review of analogue modelling of geodynamic processes: Approaches, scaling, materials and quantification, with an application to subduction experiments

“…McClay, 1990;Storti et al, 2000;Gomes, 2013), and ethyl cellulose powder (e.g. Cobbold, 1988, 1991;Ratschbacher et al, 1991;Cobbold and Jackson, 1992;Faccenna et al, 1996;Cagnard et al, 2006;Marques and Cobbold, 2006;Schueller and Davy, 2008;Bajolet et al, 2015). Other dry granular materials include aluminium microspheres (e.g.…”

Strain rate‐dependent lithosphere rifting and necking architectures in analog experiments

“…In the slow model, fast amplification rate of the necking Figure 2. Brittle-ductile parameter Γ computed for the crust (Γ C ), the lithospheric mantle (Γ M ), and the whole lithosphere (Γ L ) according to Schueller and Davy [2008]. For comparative purposes, Γ values are computed also for experiment NECK-10 described in Nestola et al [2013].…”

“…This mixing did not substantially alter the behavior of the viscous layers, since the measured rheological parameter n is 1.053 and 1.067 for the model lower crust and lower mantle, respectively, i.e., very close to the condition n = 1 that describes the Newtonian rheology [e.g., Ranalli, 1995]. In our model layering, the upper brittle crust is a 13 mm thick sand layer ( ρ C = 1200 kg m À3 and average grain size [Schueller and Davy, 2008].…”

“…In compressional settings, as those largely investigated in Schueller and Davy [2008], the Γ value of 0.5 is the threshold between localized (Γ > 0.5) and nonlocalized (Γ < 0.5). In extensional settings, the differential stress to yielding is 0.25 that in compression [Sibson, 1977].…”

“…The influence of strain rate on deformation localization is predicted by the brittle-ductile parameter Γ [Schueller and Davy, 2008], defined as…”