Rheology of Earth Materials :
Closing the gap between timescales in the laboratory and in the mantle

16 August 2022 - New publication in Acta Materialia

On the formation of intragranular amorphous shear bands in olivine

Intragranular amorphization shear lamellae are found in deformed olivine aggregates. In this study, we provide an extensive characterization by TEM of one of those lamellae which arrests inside a grain.

We show that the deformation field associated with this lamella is complex and heterogeneous, involving mode I, II and III loading components. The formation and propagation of the amorphous lamella is accompanied by the formation of crystal defects ahead of the tip. These defects are geometrically necessary [001] dislocations, characteristics of high-stress deformation in olivine, and rotational nanodomains which are tentatively interpreted as disclinations. We show that these defects play an important role in dictating the path followed by the amorphous lamella.

Stress-induced amorphization in olivine would thus result from a direct crystal-to- amorphous transformation associated with a shear instability and not from a mechanical destabilization due to the accumulation of high number of defects from an intense preliminary deformation.

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H. Idrissi, A. Béché, N. Gauquelin, I. Ul Haq, C. Bollinger, S. Demouchy, J. Verbeeck, T. Pardoen, D. Schryvers & P. Cordier (2022) On the formation mechanisms of intragranular shear bands in olivine by stress-induced amorphization. Acta Materialia, 239, 118247, https://doi.org/10.1016/j.actamat.2022.118247