Dynamic recrystallization by subgrain rotation in olivine revealed by electron backscatter diffraction

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1016/j.tecto.2021.228916. This is version 3 of this Preprint.

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Authors

Marco Antonio Lopez-Sanchez , Andrea Tommasi , Walid Ben Ismail, Fabrice Barou 

Abstract

We document how dynamic recrystallization by subgrain rotation (SGR) develops in natural olivine-rich rocks deformed in extension to up to 50% bulk finite strain (1473 K, confining pressure of 300 MPa, and stresses between 115 and 180 MPa) using electron backscatter diffraction (EBSD) mapping. SGR occurs preferentially in highly deformed grains (well-oriented to deform by dislocation glide) subjected to local stress concentrations due to interactions with hard neighbouring grains (poorly-oriented olivine crystals or pyroxenes). Subgrains (misorientation <15°) are mainly delimited by tilt walls composed of combinations of dislocations of the [100](001), [001](100), [100](010) and [001](010) systems, in order of decreasing frequency. The activation and prevalence of these systems agree with a Schmid factor analysis using data for high-T dislocation creep in olivine. The development of closed 3D subgrain cells by SGR recrystallization requires the contribution of at least three different slip systems, implying the activation of hard slip systems and high (local) stresses. The transition from subgrain to grain boundaries (misorientation ≥15°) is characterized by a sharp change in the misorientation axes that accommodate the difference in orientation between the two subgrains or grains. We propose that this change marks the creation and incorporation of new defects (grain boundary dislocations with different Burger vectors and, likely, disclinations or disconnections) at the newly-formed grain boundaries and that this might be favoured by stress concentrations due to increasing misalignment between slip systems across the boundary. Finally, we document the development of strong misorientations within the parent grains, due to the accumulation of low angle grain boundaries, and between them and the recrystallized grains. SGR recrystallization may thus produce strong dispersion of the crystal preferred orientation without the need for grain boundary sliding.

DOI

https://doi.org/10.31223/X5BW27

Subjects

Earth Sciences

Keywords

Subgrain rotation recrystallization, Geometrically necessary dislocations, Electron backscatter diffraction

Dates

Published: 2021-01-12 23:52

Last Updated: 2022-04-29 17:03

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License

CC BY Attribution 4.0 International

Additional Metadata

Conflict of interest statement:
None

Data Availability (Reason not available):
All codes for EBSD data-treatment will be provided as supplementary material and raw EBSD data will be hosted in an open-source repository with a doi link once accepted for publication.

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