Abstract
Abstract. During lithospheric extension, localization of deformation often occurs along structural weaknesses inherited from previous tectonic phases. Such weaknesses may occur in both the crust and mantle, but the combined effects of these weaknesses on rift evolution remain poorly understood. Here we present a series of 3D brittle–viscous analogue models to test the interaction between differently oriented weaknesses located in the brittle upper crust and/or upper mantle. We find that crustal weaknesses usually express first at the surface, with the formation of grabens parallel to their orientation; then, structures parallel to the mantle weakness overprint them and often become dominant. Furthermore, the direction of extension exerts minimal control on rift trends when inherited weaknesses are present, which implies that present-day rift orientations are not always indicative of past extension directions. We also suggest that multiphase extension is not required to explain different structural orientations in natural rift systems. The degree of coupling between the mantle and upper crust affects the relative influence of the crustal and mantle weaknesses: low coupling enhances the influence of crustal weaknesses, whereas high coupling enhances the influence of mantle weaknesses. Such coupling may vary over time due to progressive thinning of the lower crustal layer, as well as due to variations in extension velocity. These findings provide a strong incentive to reassess the tectonic history of various natural examples.
Highlights
Over the course of continental rifting, initial localization of deformation often occurs along structural weaknesses inherited from previous tectonic phases (e.g. Wilson, 1966; Morley et al, 1990; Nelson et al, 1992; Bonini et al, 1997; Corti, 2012)
Reference Model A, without simulated crustal weaknesses, developed early on two deformation zones on both sides of VD that became clearly visible on particle image velocimetry (PIV) images after 5 mm of extension (e = 1.7 %; Fig. 2a)
In this paper we presented a series of brittle–viscous analogue models to study how differently oriented mantle and crustal weaknesses may interact and affect rift development
Summary
Over the course of continental rifting, initial localization of deformation often occurs along structural weaknesses inherited from previous tectonic phases (e.g. Wilson, 1966; Morley et al, 1990; Nelson et al, 1992; Bonini et al, 1997; Corti, 2012). Over the course of continental rifting, initial localization of deformation often occurs along structural weaknesses inherited from previous tectonic phases Wilson, 1966; Morley et al, 1990; Nelson et al, 1992; Bonini et al, 1997; Corti, 2012) These initial weaknesses may be situated anywhere in the lithosphere, structural heterogeneities tend to be attenuated or erased at great depth where the temperature is high (T > 800 +/− 300 ◦C depending on the geothermal gradient, the nature of the rock involved and the extension rate; Braun et al, 1999; Yamakasi et al, 2006). Weaknesses in the upper lithospheric mantle range from large-scale tectonic features such as major suture zones or “mantle scars” to microscopic fabric related to preferred orientations of olivine crystals (e.g. Tommasi et al, 2009), which are found in continental lithospheres around the globe
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