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Thermal Softening Induced Strain Localization, a Possible Mechanism of Lithospheric Scale Shear Zone Formation and Subduction Initiation

Abstract : Active plate tectonics, characterized by excessive areas of no or little deformation divided by localized areas of intense deformation, is a distinctive feature of our planet. Despite its importance, the physics of lithospheric scale shear zone formation and subduction initiation is still incompletely understood. We focus on two major challenges, that are: (1) To find a mechanism of spontaneous shear localization without prescribing the shear zone. (2) Based on experimentally derived flow-laws of olivine, the upper and hence colder part of the mantle must be very strong. In fact, the stresses required to deform a yet intact and cold mantle are difficult to reach and maintain without a softening mechanism. In this study we discuss the possible role of thermal softening in subduction initiation. Thermal softening is a result of the conversion of mechanical work into heat (i.e. shear heating) and of the temperature dependence of rock viscosities. Previous studies have shown that thermal softening can cause strain localization and the formation of large-offset shear zones in ductile materials whose deformation behavior is described with creep flow laws (e.g. dislocation creep). Also, it has been shown that thermal softening induced shear localization can result in significant stress drops of a few hundred MPa. We present a one-dimensional (1D), simple shear model that helps both qualitative and quantitative understanding of the first order characteristics of shear zone evolution. We show the general applicability of the 1D simple-shear model by comparing it’s results with 2D and 3D of shear zone development under far-field pure shear. Finally, we compare the results of the simple shear zone models with results of high resolution numerical simulations of Alpine lithospheric deformation. In these simulations, first we model the formation of hyper-extended passive margins and mantle exhumation by extending a continental lithosphere. After a period of thermal relaxation, we start to compress the resulted configuration which leads to subduction initiation. From the onset of the subduction until the continent-continent collision a strong positive thermal anomaly, associated with thermal softening, is located at the subduction interface.
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Contributor : Isabelle Dubigeon <>
Submitted on : Tuesday, November 20, 2018 - 9:42:31 AM
Last modification on : Friday, April 5, 2019 - 8:18:06 PM

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  • HAL Id : insu-01927709, version 1

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Daniel Kiss, Lorenzo Candioti, Thibault Duretz, Yuri Podlachikov, Stefan Markus Schmalholz. Thermal Softening Induced Strain Localization, a Possible Mechanism of Lithospheric Scale Shear Zone Formation and Subduction Initiation. American Geophysical Union 2018, Fall Meeting, Dec 2018, Washington, United States. pp.T44A-08. ⟨insu-01927709⟩

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