DOI: 10.5194/tc-15-303-2021
论文题名: Full crystallographic orientation (c and a axes) of warm, coarse-grained ice in a shear-dominated setting: A case study, Storglaciären, Sweden
作者: Monz M.E. ; Hudleston P.J. ; Prior D.J. ; Michels Z. ; Fan S. ; Negrini M. ; Langhorne P.J. ; Qi C.
刊名: Cryosphere
ISSN: 19940416
出版年: 2021
卷: 15, 期: 1 起始页码: 303
结束页码: 324
语种: 英语
英文关键词: cryosphere
; crystallography
; ice cover
; Norrbotten
; Storglaciaren
; Sweden
英文摘要: Microstructures provide key insights into understanding the mechanical behavior of ice. Crystallographic preferred orientation (CPO) develops during plastic deformation as ice deforms dominantly by dislocation glide on the basal plane, modified and often intensified by dynamic recrystallization. CPO patterns in fine-grained ice have been relatively well characterized and understood in experiments and nature, whereas CPO patterns in "warm"(T > -10°C), coarse-grained, natural ice remain enigmatic. Previous microstructural studies of coarse-grained ice have been limited to c-axis orientations using light optical measurements. We present the first study of a axes as well as c axes in such ice by application of cryo-electron backscatter diffraction (EBSD) and do so in a shear-dominated setting. We have done this by developing a new sample preparation technique of constructing composite sections, to allow us to use EBSD to obtain a representative, bulk CPO on coarse-grained ice. We draw attention to the well-known issue of interlocking grains of complex shape and suggest that a grain sampling bias of large, branching crystals that appear multiple times as island grains in thin sections may result in the typical multimaxima CPOs previously identified in warm, coarsegrained ice that has been subjected to prolonged shear. CPOs combined from multiple samples of highly sheared ice from Storglaciären provide a more comprehensive picture of the microstructure and yield a pronounced cluster of c axes subnormal to the shear plane and elongate or split in a plane normal to the shear direction as well as a concomitant girdle of a axes parallel to the shear plane with a maximum perpendicular to the shear direction. This pattern compares well with patterns produced by subsampling datasets from ice sheared in laboratory experiments at high homologous temperatures up to strains of ∼ 1.5. Shear strains in the margin of Storglaciären are much higher than those in experimental work. At much lower natural strain rates, dynamic recrystallization, particularly grain boundary migration, may have been more effective so that the CPO represents a small, final fraction of the shear history. A key result of this study is that multimaxima CPOs in coarse-grained ice reported in previous work may be due to limited sample sizes and a sampling bias related to the presence of island grains of a single host that appear several times in a thin section. © Author(s) 2021. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/164764
Appears in Collections: 气候变化与战略
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作者单位: Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN, United States; Department of Geology, University of Otago, Dunedin, New Zealand; Key Laboratory of Earth and Planetary Physics, Chinese Academy of Sciences, Beijing, China
Recommended Citation:
Monz M.E.,Hudleston P.J.,Prior D.J.,et al. Full crystallographic orientation (c and a axes) of warm, coarse-grained ice in a shear-dominated setting: A case study, Storglaciären, Sweden[J]. Cryosphere,2021-01-01,15(1)