Structural reactivation in plate tectonics controlled by olivine crystal anisotropy

Abstract

International audienceReactivation of structures inherited from previous collisional or rifting events, especially lithospheric-scale faults, is a major feature of plate tectonics. Its expression ranges from continental break-up along ancient collisional belts(1,2) to linear arrays of intraplate magmatism and seismicity(3,4). Here we use multiscale numerical models to show that this reactivation can result from an anisotropic mechanical behaviour of the lithospheric mantle due to an inherited preferred orientation of olivine crystals. We explicitly consider an evolving anisotropic viscosity controlled by the orientation of olivine crystals in the mantle. We find that strain is localized in domains where shear stresses on the inherited mantle fabric are high, and that this leads to shearing parallel to the inherited fabric. During rifting, structural reactivation induced by anisotropy results in oblique extension, followed by either normal extension or failure. Our results suggest that anisotropic viscosity in the lithospheric mantle controls the location and orientation of intraplate deformation zones that may evolve into new plate boundaries, and causes long-lived lithospheric-scale wrench faults, contributing to the toroidal component of plate motions on Earth

Small quantity but large effect — How minor phases control strain localization in upper mantle shear zones

“…Other parameters like overall energy available to deform a given rock volume (Regenauer-Lieb and Yuen, 2004;Regenauer-Lieb et al 2012), the inheritance of mechanical anisotropies (Michibayashi and Mainprice, 2004;Tommasi et al, 2009;Vauchez et al, 1998), or the presence of water or melts (Dijkstra, 2001;Mei and Kohlstedt, 2000a) need to be considered to explain strain localization in the upper mantle at elevated temperatures.…”

Modeling the effect of subgrain rotation recrystallization on the evolution of olivine crystal preferred orientations in simple shear

“…Existence of preferred orientation of olivine crystals at large scale should therefore result in an anisotropic thermomechanical behavior of the upper mantle. Numerical models of lithospheric deformation that explicitly consider an evolving CPOinduced mechanical anisotropy display indeed strain localization depending on the orientation of the olivine CPO relatively to the applied stresses Tommasi et al, 2009). They also show a high sensitivity of the strain distribution to the evolution of the CPO .…”

Perpectives on Integrated Solid Earth Sciences

“…The resulting anisotropic propagation of seismic waves has been largely used to map the deformation in the mantle in the last 25 years (e.g., Kendall et al, 2005). In contrast, the studies on the consequences and possible uses of the anisotropy of electrical and thermal conductivities or of an anisotropic viscosity in the upper mantle are still in their infancy, but a large number of promising results Garrido et al, 2009) have been published recently (e.g., Tommasi et al, 2001;Gatzemeier and Tommasi, 2006;Baba et al, 2006;Petitjean et al, 2006;Lev and Hager, 2008;Tommasi et al, 2009). …”