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$Synchrotron X-ray Microdiffraction and Fluorescence Imaging of Mineral and Rock Samples$

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Published on: June 19, 2018

Geometrically necessary dislocation densities in olivine obtained using high-angular resolution electron backscatter

David Wallis¹, Lars N Hansen¹, T Ben Britton²

¹Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, Oxfordshire, OX1 3AN, UK.

Ultramicroscopy

|June 24, 2016

Summary

This summary is machine-generated.

High-angular resolution electron backscatter diffraction (HR-EBSD) offers a new way to study dislocations in olivine, a key mineral in Earth's mantle. This technique accurately quanties dislocation densities and distributions, improving our understanding of geological deformation.

Keywords:

Cross-correlation Dislocation density Electron backscatter diffraction Geological materials HR-EBSD Olivine slip systems

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Area of Science:

Geophysics
Materials Science
Mineral Physics

Background:

Dislocations in geological minerals drive creep processes crucial for geodynamics.
Quantifying dislocation densities, distributions, and types at various scales is challenging.
Conventional techniques have limitations in resolving fine dislocation structures.

Purpose of the Study:

To develop and test the application of high-angular resolution electron backscatter diffraction (HR-EBSD) for analyzing dislocations in olivine.
To evaluate different inversion methods for estimating geometrically necessary dislocation (GND) densities in olivine.
To assess the sensitivity and resolution capabilities of HR-EBSD for various olivine dislocation structures.

Main Methods:

Utilized high-angular resolution electron backscatter diffraction (HR-EBSD) with improved angular resolution (<0.01°).
Applied diffraction pattern cross-correlation for enhanced analysis of crystallographic orientation data.
Tested various data acquisition settings and inversion methods for estimating geometrically necessary dislocation (GND) densities.

Main Results:

HR-EBSD successfully quantified dislocation densities and distributions in olivine, even at very low densities.
The technique demonstrated the ability to resolve diverse olivine dislocation structures.
GND density estimates were well-constrained due to olivine's crystal symmetry and limited slip systems.
Noise floor for GND density was inversely proportional to map step size, allowing optimization for different structures.

Conclusions:

HR-EBSD is a powerful and effective method for analyzing dislocations in olivine.
The technique provides more detailed structural information than conventional methods like dislocation decoration.
HR-EBSD enhances our understanding of the role of dislocations in accommodating macroscopic deformation in Earth's upper mantle.