Time for anisotropy: The significance of mechanical anisotropy for the development of deformation structures

Abstract

This is a repository copy of Time for anisotropy: The significance of mechanical anisotropy for the development of deformation structures.

A review of numerical modelling of the dynamics of microstructural development in rocks and ice: Past, present and future

“…The VPFFT is a spectral method that specifically assumes that deformation is achieved by dislocation glide on crystallographic slip planes (each with their own critical resolved shear stress) whose orientations are mapped on a regular grid (for details see Griera et al 2013, Montagnat et al (2011Montagnat et al ( , 2014 and Llorens et al (2016a)). The simulations of Griera et al (2011Griera et al ( , 2013 and Ran et al (2018) illustrate that heterogeneous stress within and between grains that emerge from inhomogeneous slip has a significant effect on the rotation rate of porphyroclasts and -blasts and the strain (rate) field around these objects. leading to strain localisation bands that can be masked by GBM (Llorens et al, 2016b).…”

“…It was found that, due to the vorticity of deformation, it is expected that ice is effectively weaker in the lower parts of ice sheets (where simple shear dominates) than in the upper parts (where ice is mostly deformed coaxially). The method was also applied to reproduce the development of tilted-lattice (kink) bands found in ice cores (Jansen et al, 2016) and crenulation cleavage during folding (Ran et al, 2018) as a result of mechanical anisotropy. Steinbach et al (2016) included air inclusions as a second phase to simulate DRX in porous firn and found that DRX can occur despite the low strain and stress in firn.…”

“…Upscaling this approach to investigate problems at a large scale e.g. folding (Llorens et al, 2013a(Llorens et al, , 2013bBons et al, 2016;Ran et al, 2018) and shear deformation (Gardner et al, 2017) have shown to be very beneficial. There is great scope to expand further on this in view of fluid flow, mineralization and fault formation.…”

“…Abbreviations: TBH - Taylor Such "micro-shear zones" may now have been detected in polar ice sheets as well (Weikusat et al, 2009). Jessell et al, 2001;Jessell and Bons, 2002;Bons et al, 2008;Piazolo et al, 2010 Single processes Crystal lattice rotation for single phase D D slip, rotation, translation TBH Etchecopar, 1977Lister and Paterson, 1979D VPFFT Lebensohn et al, 2001Montagnat et al ,2011, 2014D VPFFT -3D Roters et al, 2012Eisenlohr et al, 2013 Grain rotations for two phases D VPFFT Griera et al, 2011Griera et al, , 2013Griera et al, , 2015Ran et al, 2018 Elasto-viscoplastic Ford et al, 2002Wheeler, 2009, 2010 Diffusion creep for two phases D front tracking Berton et al, 2006Berton et al, , 2011 Dissolution and/or precipitation D lattice spring model Koehn et al, 2006Koehn et al, , 2007Koehn et al, , 2012Koehn et al, , 2016Ebner et al, 2009 FEMthin sheet model Houseman, 1992, 1996 Grain boundary diffusion S finite difference Park et al, 2004 Strain/stress localisation D VPFFT Griera et al, 2011Griera et al, , 2015Ran et al, 2018 Combination of Processes Intracrystalline recovery and subgrain rotation S Potts-like Borthwick et al, 2013 Ductile deformation and grain growthpolyphase D FEM + front tracking Groome et al, 2006;Smith et al, 2015 Dynamic reXX: -crystal plastic deformation, grain boundary migration, rotation recrystallization D TBH+Potts-like Jessell, 1988a...…”

A stratigraphy-based method for reconstructing ice core orientation

“…form by lateral shortening of thin laminations in rocks or a foliation defined by strongly anisotropic minerals, such as micas (Cosgrove, 1976;Ran and others, 2019) or ice (Bons and others, 2016). The automated method for tilt measurements was verified manually on 30 random samples.…”