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Solid Earth An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/se-2019-168
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2019-168
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 11 Nov 2019

Submitted as: research article | 11 Nov 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Solid Earth (SE).

The variation and visualisation of elastic anisotropy in rock forming minerals

David Healy1, Nicholas E. Timms2, and Mark A. Pearce3 David Healy et al.
  • 1School of Geosciences, King's College, University of Aberdeen, Aberdeen AB24 3UE, UK
  • 2Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Perth, GPO Box U1987, WA 6845, Australia
  • 3SIRO Mineral Resources, Australian Resources Research Centre, 26 Dick Perry Avenue, Kensington, WA 6151, Australia

Abstract. All minerals behave elastically, a rheological property that controls their ability to support stress, strain and pressure, the nature of acoustic wave propagation and influences subsequent plastic (i.e. permanent, non-reversible) deformation. All minerals are intrinsically anisotropic in their elastic properties – that is, they have directional variations that are related to the configuration of the crystal lattice. This means that the commonly used mechanical elastic properties that relate elastic stress to elastic strain, including Young's modulus (E), Poisson's ratio (ν), shear modulus (G) and linear compressibility (β), are dependent on crystallographic direction. In this paper, we explore the ranges of anisotropy of E, ν, G and β in 86 rock-forming minerals, using previously published data, and show that the range is much wider than commonly assumed. We also explore how these variations (the directionality and the magnitude) are important for fundamental processes in the solid earth, including deformation (mechanical) twinning, coherent phase transformations and brittle failure. We present a new open source software package (AnisoVis, written in MATLAB), which we use to calculate and visualise directional variations in elastic properties of rock-forming minerals. Following previous work in the fields of chemistry and materials, we demonstrate that by visualising the variations in elasticity, we discover previously unreported properties of rock forming minerals. For example, we show previously unreported directions of negative Poisson's ratio and negative linear compressibility and we show that the existence of these features is more widespread (i.e. present in many more minerals) than previously thought. We illustrate the consequences of intrinsic elastic anisotropy for the elastic normal and shear strains within α-quartz single crystal under different applied stress fields; the role of elastic anisotropy on Dauphiné twinning and the α-β phase transformations in quartz; and stress distributions around voids of different shapes in talc, lizardite, albite, and sanidine. In addition to our specific examples, elastic anisotropy in rock-forming minerals to the degree that we describe has significant consequences for seismic (acoustic) anisotropy, the focal mechanisms of earthquakes in anisotropic source regions (e.g. subducting slabs), for a range of brittle and ductile deformation mechanisms in minerals, and geobarometry using mineral inclusions.

David Healy et al.
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Short summary
All rock forming minerals behave elastically, a property that controls their ability to support stress and strain, the transmission of seismic waves, and influences subsequent permanent deformation. All minerals are intrinsically anisotropic in their elastic properties – that is, they have directional variations that are related to the crystal lattice. We explore this directionality, and present new ways of visualising it. We hope this will enable further advances in understanding deformation.
All rock forming minerals behave elastically, a property that controls their ability to support...
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