Dynamic recrystallization by subgrain rotation in olivine revealed by high-spatial resolution electron backscatter diffraction

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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 115-180 MPa) using high-resolution 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 grains (poorly-oriented olivine crystals or pyroxenes). Subgrains (misorientation <15°) are delimited mainly by tilt walls composed by 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 values for high-T deformation 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 subgrains 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 possibly disclinations or disconnections) at the newly-formed grain boundaries. This process might be favoured by stress concentrations at the grain boundaries due to increasing misalignment between slip systems in parent and recrystallized grains. Finally, we document the development of strong misorientations due to accumulation of low angle grain boundaries within the parent grains and between them and the recrystallized ones. This process leads to intense dispersion of the crystal preferred orientation resulting from SGR alone, with no involvement of 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 15:52

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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