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

By
A. Vauchez
A. Vauchez
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A. Tommasi
A. Tommasi
Laboratoire de Tectonophysique, Université de Montpellier II et CNRS Pl. Eugène Bataillon, F-34095 Montpellier cedex 5, France
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Published:
January 01, 2003

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.

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Geological Society, London, Special Publications

Intraplate Strike-Slip Deformation Belts

F. Storti
F. Storti
Università degli Studi “Roma Tre”, Rome, Italy
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R. E. Holdsworth
R. E. Holdsworth
Durham University, Durham, UK
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F. Salvini
F. Salvini
Università degli Studi “Roma Tre”, Rome, Italy
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Geological Society of London
Volume
210
ISBN electronic:
9781862394582
Publication date:
January 01, 2003

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