EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice
Ice has a very high plastic anisotropy with easy dislocation glide on basal planes, while glide on non-basal planes is much harder. Basal glide involves dislocations with the Burgers vector b = 〈 a 〉, while glide on non-basal planes can involve dislocations with b = 〈 a 〉, b = [ c ], and b = 〈 c + a...
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ftcopernicus:oai:publications.copernicus.org:se57143 2023-05-15T13:54:27+02:00 EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice Weikusat, Ilka Kuiper, Ernst-Jan N. Pennock, Gill M. Kipfstuhl, Sepp Drury, Martyn R. 2018-09-27 application/pdf https://doi.org/10.5194/se-8-883-2017 https://se.copernicus.org/articles/8/883/2017/ eng eng doi:10.5194/se-8-883-2017 https://se.copernicus.org/articles/8/883/2017/ eISSN: 1869-9529 Text 2018 ftcopernicus https://doi.org/10.5194/se-8-883-2017 2020-07-20T16:23:37Z Ice has a very high plastic anisotropy with easy dislocation glide on basal planes, while glide on non-basal planes is much harder. Basal glide involves dislocations with the Burgers vector b = 〈 a 〉, while glide on non-basal planes can involve dislocations with b = 〈 a 〉, b = [ c ], and b = 〈 c + a 〉. During the natural ductile flow of polar ice sheets, most of the deformation is expected to occur by basal slip accommodated by other processes, including non-basal slip and grain boundary processes. However, the importance of different accommodating processes is controversial. The recent application of micro-diffraction analysis methods to ice, such as X-ray Laue diffraction and electron backscattered diffraction (EBSD), has demonstrated that subgrain boundaries indicative of non-basal slip are present in naturally deformed ice, although so far the available data sets are limited. In this study we present an analysis of a large number of subgrain boundaries in ice core samples from one depth level from two deep ice cores from Antarctica (EPICA-DML deep ice core at 656 m of depth) and Greenland (NEEM deep ice core at 719 m of depth). EBSD provides information for the characterization of subgrain boundary types and on the dislocations that are likely to be present along the boundary. EBSD analyses, in combination with light microscopy measurements, are presented and interpreted in terms of the dislocation slip systems. The most common subgrain boundaries are indicative of basal 〈 a 〉 slip with an almost equal occurrence of subgrain boundaries indicative of prism [ c ] or 〈 c + a 〉 slip on prism and/or pyramidal planes. A few subgrain boundaries are indicative of prism 〈 a 〉 slip or slip of 〈 a 〉 screw dislocations on the basal plane. In addition to these classical polygonization processes that involve the recovery of dislocations into boundaries, alternative mechanisms are discussed for the formation of subgrain boundaries that are not related to the crystallography of the host grain. The finding that subgrain boundaries indicative of non-basal slip are as frequent as those indicating basal slip is surprising. Our evidence of frequent non-basal slip in naturally deformed polar ice core samples has important implications for discussions on ice about plasticity descriptions, rate-controlling processes which accommodate basal glide, and anisotropic ice flow descriptions of large ice masses with the wider perspective of sea level evolution. Text Antarc* Antarctic Antarctica DML EPICA Greenland ice core Copernicus Publications: E-Journals Antarctic Greenland Solid Earth 8 5 883 898 |
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Open Polar |
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Copernicus Publications: E-Journals |
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ftcopernicus |
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English |
description |
Ice has a very high plastic anisotropy with easy dislocation glide on basal planes, while glide on non-basal planes is much harder. Basal glide involves dislocations with the Burgers vector b = 〈 a 〉, while glide on non-basal planes can involve dislocations with b = 〈 a 〉, b = [ c ], and b = 〈 c + a 〉. During the natural ductile flow of polar ice sheets, most of the deformation is expected to occur by basal slip accommodated by other processes, including non-basal slip and grain boundary processes. However, the importance of different accommodating processes is controversial. The recent application of micro-diffraction analysis methods to ice, such as X-ray Laue diffraction and electron backscattered diffraction (EBSD), has demonstrated that subgrain boundaries indicative of non-basal slip are present in naturally deformed ice, although so far the available data sets are limited. In this study we present an analysis of a large number of subgrain boundaries in ice core samples from one depth level from two deep ice cores from Antarctica (EPICA-DML deep ice core at 656 m of depth) and Greenland (NEEM deep ice core at 719 m of depth). EBSD provides information for the characterization of subgrain boundary types and on the dislocations that are likely to be present along the boundary. EBSD analyses, in combination with light microscopy measurements, are presented and interpreted in terms of the dislocation slip systems. The most common subgrain boundaries are indicative of basal 〈 a 〉 slip with an almost equal occurrence of subgrain boundaries indicative of prism [ c ] or 〈 c + a 〉 slip on prism and/or pyramidal planes. A few subgrain boundaries are indicative of prism 〈 a 〉 slip or slip of 〈 a 〉 screw dislocations on the basal plane. In addition to these classical polygonization processes that involve the recovery of dislocations into boundaries, alternative mechanisms are discussed for the formation of subgrain boundaries that are not related to the crystallography of the host grain. The finding that subgrain boundaries indicative of non-basal slip are as frequent as those indicating basal slip is surprising. Our evidence of frequent non-basal slip in naturally deformed polar ice core samples has important implications for discussions on ice about plasticity descriptions, rate-controlling processes which accommodate basal glide, and anisotropic ice flow descriptions of large ice masses with the wider perspective of sea level evolution. |
format |
Text |
author |
Weikusat, Ilka Kuiper, Ernst-Jan N. Pennock, Gill M. Kipfstuhl, Sepp Drury, Martyn R. |
spellingShingle |
Weikusat, Ilka Kuiper, Ernst-Jan N. Pennock, Gill M. Kipfstuhl, Sepp Drury, Martyn R. EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice |
author_facet |
Weikusat, Ilka Kuiper, Ernst-Jan N. Pennock, Gill M. Kipfstuhl, Sepp Drury, Martyn R. |
author_sort |
Weikusat, Ilka |
title |
EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice |
title_short |
EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice |
title_full |
EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice |
title_fullStr |
EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice |
title_full_unstemmed |
EBSD analysis of subgrain boundaries and dislocation slip systems in Antarctic and Greenland ice |
title_sort |
ebsd analysis of subgrain boundaries and dislocation slip systems in antarctic and greenland ice |
publishDate |
2018 |
url |
https://doi.org/10.5194/se-8-883-2017 https://se.copernicus.org/articles/8/883/2017/ |
geographic |
Antarctic Greenland |
geographic_facet |
Antarctic Greenland |
genre |
Antarc* Antarctic Antarctica DML EPICA Greenland ice core |
genre_facet |
Antarc* Antarctic Antarctica DML EPICA Greenland ice core |
op_source |
eISSN: 1869-9529 |
op_relation |
doi:10.5194/se-8-883-2017 https://se.copernicus.org/articles/8/883/2017/ |
op_doi |
https://doi.org/10.5194/se-8-883-2017 |
container_title |
Solid Earth |
container_volume |
8 |
container_issue |
5 |
container_start_page |
883 |
op_container_end_page |
898 |
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1766260320123224064 |