Narrow rifts versus wide rifts: inferences for the mechanics of rifting from laboratory experiments

Abstract

Laboratory experiments on analogue models of the lithosphere are useful tools to study tectonic processes and, in particular, to test physical hypotheses. They complement numerical modelling because the inherent limitations of each method are different. The basic principles of the method are recalled with particular application to models simulating the brittle-ductile layering of continental crust and lithosphere using sand and silicone putties to simulate the frictional and viscous behaviour of rocks. A selection of experiments is used to examine the role of rheology on the development of crustal-scale extensional structures: continental rifts, passive margins, wide extended domains, and core complexes. The difference between narrow rifts and wide rifts is attributed to the type of mechanical instability that can develop for a given type of lithospheric strength profile: namely necking versus spreading. Necking occurs preferentially in a stable lithosphere that has a four-layer-type of strength profile with the greatest strength located in the sub-Moho mantle. It gives birth to narrow rifts, from continental rifts to passive margins. Spreading occurs preferentially in a thickened lithosphere whose strength profile, after thermal relaxation, exhibits maximum strength at the base of upper brittle crust. It gives birth to wide rifts, such as the Basin and Range of the western United States or the Aegean. Core complexes are not considered to represent a particular mode of extension but are anomalies in wide rifts.

How oblique extension and structural inheritance influence rift segment interaction: Insights from 4D analog models

“…High brittle-ductile coupling due to high strain rates or high viscosities in the ductile domain causes distributed deformation (wide rifting) in the brittle parts of the crust (Brun, 1999;Buiter et al, 2008), preventing the development of discrete fault zones (Allken et al, 2011;2012;Zwaan et al, 2016). It is thus necessary to decrease deformation rates in our analog models in order to limit wide rifting effects, as shown in Fig candidate at the University of Bern (Switzerland), studying the effects of oblique extension and scissor tectonics on rift interaction and rift propagation with the use of analog models and Xray CT techniques.…”

“…When angle α is 0°, extension is orthogonal. We apply an extension velocity of 3 mm∕h to better localize deformation, eliminating the effects due to high brittle-ductile coupling and the associated wide rifting (Brun, 1999;Buiter et al, 2008;Figure A-1). As it is standard in most physical rifting models, the extension rate is constant along the whole length of our models.…”

“…The overlap or underlap of rift segments (see also Figure 2d, 2e, and 2i) can result in a variation of rift interaction zone structures and can cause the formation of microcontinents (Müller et al, 2001;Tentler and Acocella, 2010). In addition, strong brittle-ductile coupling due to either high viscosities in the lower crust or high extension velocities (Brun, 1999;Buiter et al, 2008) causes distributed deformation (wide rifting) and prevents rift segments from developing discrete transfer zones (Allken et al, 2011(Allken et al, , 2012Zwaan et al, 2016).…”

Effects of mass waste events on thrust wedges: Analogue experiments and application to the Makran accretionary wedge

“…Being left with large uncertainties and following other experimentalists [e.g., Bonini, 2001;Costa and Vendeville, 2002;Fort et al, 2004], we employed very weak (viscosity m = 2.4 × 10 4 Pa s at laboratory temperature) Newtonian viscous silicone putty as analog to overpressured layers. Indeed, experimental results are discussed in the light of first-order stress distribution and shear stress contrast between adjacent layers [e.g., Davy and Cobbold, 1991;Brun, 1999], leaving aside the question of exact rheological properties of natural samples and, therefore, that of the strict rheological similarity between prototype and model.…”

“…[24] Previous experimental studies have analyzed the effects of brittle-ductile coupling in terms of relative strength between the brittle and ductile layers in both extensional [Nalpas and Brun, 1993;Brun, 1999Brun, , 2002 and compression settings [Bonini, 2001;Smit et al, 2003]. This approach allows taking into account lateral variations in rheology and geometry of separate layers.…”