Vaughan, MJ;
Prior, DJ;
Jefferd, M;
Brantut, N;
Mitchell, TM;
Seidemann, M;
(2017)
Insights into anisotropy development and weakening of ice from in situ P wave velocity monitoring during laboratory creep.
Journal of Geophysical Research: Solid Earth
, 122
(9)
pp. 7076-7089.
10.1002/2017JB013964.
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Abstract
Polycrystalline ice weakens significantly after a few percent strain, during high homologous temperature deformation. Weakening is correlated broadly with the development of a crystallographic preferred orientation (CPO). We deformed synthetic polycrystalline ice at -5°C under uniaxial compression, while measuring ultrasonic P wave velocities along several raypaths through the sample. Changes in measured P wave velocities (V p ) and in the velocities calculated from microstructural measurements of CPO (by cryo-electron backscatter diffraction) both show that velocities along trajectories parallel and perpendicular to shortening decrease with increasing strain, while velocities on diagonal trajectories increase. Thus, in these experiments, velocity data provide a continuous measurement of CPO evolution in creeping ice. Samples reach peak stresses after 1% shortening. Weakening corresponds to the start of CPO development, as indicated by divergence of P wave velocity changes for different raypaths, and initiates at ≈3% shortening. Selective growth by strain-induced grain boundary migration (GBM) of grains favorably oriented for basal slip may initiate weakening through the formation of an interconnected network of these grains by 3% shortening. After weakening initiates, CPO continues to develop by GBM and nucleation processes. The resultant CPO has an open cone (small circle) configuration, with the cone axis parallel to shortening. The development of this CPO causes significant weakening under uniaxial compression, where the shear stresses resolved on the basal planes (Schmid factors) are high.
| Type: | Article |
|---|---|
| Title: | Insights into anisotropy development and weakening of ice from in situ P wave velocity monitoring during laboratory creep |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1002/2017JB013964 |
| Publisher version: | http://dx.doi.org/10.1002/2017JB013964 |
| Language: | English |
| Additional information: | Copyright © 2017 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. |
| Keywords: | creep; ice; velocity; EBSD; CPO; anisotropy |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10024947 |
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