Wrench faults down to the asthenosphere: geological and geophysical evidence and thermomechanical effects

Abstract

We review a set of geological and geophysical observations that strongly support a coherent deformation of the entire lithosphere in major intracontinental wrench faults. Tectonic studies of wrench faults eroded down to the middle to lower crust show that, even in cases in which the lower to middle crust is partially melted, strain remains localized (although less efficiently) in transcurrent shear zones. Seismic profiling as well as seismic tomography and magnetotelluric soundings provide strong argument in favour of major wrench faults crosscutting the Moho and deforming the upper mantle. Pn velocity anisotropy, shear-wave splitting and electric conductivity anisotropy measurements over major wrench faults and in transpressional domains support that a wrench fault fabric exists over most or even the entire lithosphere thickness. These seismic and electrical anisotropies are generated by a crystallographic preferred orientation of olivine and pyroxenes developed in the mantle during the fault activity, which is frozen in the lithospheric mantle when the deformation stops. The preservation of such a 'wrench fault type' fabric within the upper mantle may have major effects on the subsequent tectonothermal behaviour of continents, because olivine is mechanically and thermally anisotropic. Indeed, the association of numerical models and laboratory data on textured mantle rocks strongly suggests that the orogenic continental lithosphere is an anisotropic medium with regards to its stiffness and to heat diffusion. This anisotropy may explain the frequent reactivation, at the continents scale, of ancient lithospheric-scale wrench faults and transpressional belts during subsequent tectonic events.

Accommodation of lithospheric shortening on Mercury from altimetric profiles of ridges and lobate scarps measured during MESSENGER flybys 1 and 2

“…In fact, a temperature anomaly will dissipate over a time scale dt = qC p dx 2 /k, where dx represents the width of the anomaly. If we assume a conservative dx = 10 km, at the upper end of the widths of ductile shear zones on Earth (i.e., Vauchez and Tommasi, 2003), a temperature anomaly would dissipate in only 3 Ma, regardless of the anomaly. Thus, there is no point to considering a heat retention time scale of more than a few million years, as heat loss dominates over longer times.…”

Oblique reactivation of lithosphere-scale lineaments controls rift physiography – The upper crustal expression of the Sorgenfrei-Tornquist Zone, offshore southern Norway

“…Transtensional strike-slip systems in nature and in experimental models often 490 display anastomosing, duplex geometries, where strain is distributed along a series of discrete structures that link in both strike and dip directions (e.g. Naylor et al, 1986;Richard et al, 1995;Schreurs, 2003;Vauchez and Tommasi, 2003;Mann, 2007;Wu et al, 2009;Scholz et al, 2010;Dooley and Schreurs, 2012;Chamberlain et al, 2014;Corti and Dooley, 2015;Cheng et al, 2017). However, due to BJU erosion, we can only confirm prior strike-slip activity between the laterally offset N-S striking faults, i.e.…”

“…In addition, numerous studies show that strike-slip and oblique fault systems can dissect the whole 605 lithosphere and are often associated with pervasive fabrics within mantle lithosphere (Wylegalla et al, 1999;Tommasi and Vauchez, 2001;Vauchez and Tommasi, 2003). Examples from the Great Glen Fault, UK (Klemperer and Hobbs, 1991;McBride, 1995), the Transbrasiliano fault zone, onshore Brazil (Daly et al, 2014), and the San Andreas fault system, USA (Chamberlain et al, 2014), represent crustal-terrane separating fault systems that extend down to at least the base of the crust and, in many cases, into sub-crustal lithosphere 610 (Vauchez and Tommasi, 2003). These lithosphere-scale structures are often oriented oblique to regional tectonic events and are thus subjected to oblique stresses; as such, they are often reactivated in a transpressional or transtensional manner, resulting in complex rifts at upper crustal levels (e.g.…”

“…These lithosphere-scale structures are often oriented oblique to regional tectonic events and are thus subjected to oblique stresses; as such, they are often reactivated in a transpressional or transtensional manner, resulting in complex rifts at upper crustal levels (e.g. Underhill and Brodie, 1993;Holdsworth et al, 2001;Vauchez and Tommasi, 2003;Bergerat et al, 2007;Le Breton et al, 2013;Corti and Dooley, 2015;Calignano et al, 2017;Cheng et al, 2017).…”

Postseismic deformation and the strength of ductile shear zones

“…For instance, after the 1999İzmit (Turkey) earthquake, Bürgmann et al (2002) document slip occurring in two main patches, one located at ∼15 km depth below the epicenter, the other at 35 km depth at a kink in the fault trace. Yagi et al (2003) also document postseismic deformation in the area downdip of the 1994 SanrikuHaruka-Oki rupture. In summary, recognizing the inherent non-uniqueness of inversion results, it is at least possible that transient postseismic deformation observed by GPS occurs in a localized shear zone below the seismogenic zone.…”