Stress-induced amorphization triggers deformation in the lithospheric mantle

Vahid Samae, Patrick Cordier (), Sylvie Demouchy, Caroline Bollinger, Julien Gasc, Sanae Koizumi, Alexandre Mussi, Dominique Schryvers and Hosni Idrissi
Additional contact information
Vahid Samae: University of Antwerp
Patrick Cordier: Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207, UMET, Unité Matériaux et Transformations
Sylvie Demouchy: Géosciences Montpellier, Université de Montpellier, CNRS, UMR
Caroline Bollinger: Universität Bayreuth
Julien Gasc: Géosciences Montpellier, Université de Montpellier, CNRS, UMR
Sanae Koizumi: University of Tokyo
Alexandre Mussi: Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207, UMET, Unité Matériaux et Transformations
Dominique Schryvers: University of Antwerp
Hosni Idrissi: University of Antwerp

Nature, 2021, vol. 591, issue 7848, 82-86

Abstract: Abstract The mechanical properties of olivine-rich rocks are key to determining the mechanical coupling between Earth’s lithosphere and asthenosphere. In crystalline materials, the motion of crystal defects is fundamental to plastic flow1–4. However, because the main constituent of olivine-rich rocks does not have enough slip systems, additional deformation mechanisms are needed to satisfy strain conditions. Experimental studies have suggested a non-Newtonian, grain-size-sensitive mechanism in olivine involving grain-boundary sliding5,6. However, very few microstructural investigations have been conducted on grain-boundary sliding, and there is no consensus on whether a single or multiple physical mechanisms are at play. Most importantly, there are no theoretical frameworks for incorporating the mechanics of grain boundaries in polycrystalline plasticity models. Here we identify a mechanism for deformation at grain boundaries in olivine-rich rocks. We show that, in forsterite, amorphization takes place at grain boundaries under stress and that the onset of ductility of olivine-rich rocks is due to the activation of grain-boundary mobility in these amorphous layers. This mechanism could trigger plastic processes in the deep Earth, where high-stress conditions are encountered (for example, at the brittle–plastic transition). Our proposed mechanism is especially relevant at the lithosphere–asthenosphere boundary, where olivine reaches the glass transition temperature, triggering a decrease in its viscosity and thus promoting grain-boundary sliding.

Date: 2021
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DOI: 10.1038/s41586-021-03238-3

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