scholarly journals Ice-Fabric Study of the Mawson Region, East Antarctica

1969 ◽  
Vol 8 (53) ◽  
pp. 253-276 ◽  
Author(s):  
K. Kizaki
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Ice Sheet ◽  
Secondary Recrystallization ◽  
East Antarctica ◽  
Strain Rates ◽  
Fine Grained ◽  
Single Maximum ◽  
Multiple Maxima

Attempts are made to test the relation predicted by Brace (1960) between strain-rates and the ice-fabric patterns obtained at Mawson station, east Antarctica. These orientation fabrics not only are hardly related to the prediction by Brace (1960) or Kamb (1959) but also change easily within a strain grid with 100m diagonals.Stable patterns of two- and three-maximum fabrics are confirmed. The latter is common and stable in the coarse ice at the surface of the ice sheet. It is apparent that the fabric patterns are generally related to the grain-size. The single-maximum fabric always occurs in fine-grained ice, then more maxima are formed in the course of grain growth.It appears that syntectonic-secondary recrystallization is effective in producing the orientation fabrics with two, three and multiple maxima. Also, the maxima always shift away from the pole of foliation as grain-size increases and there are several stable positions of maximum such as 0°, 17°, 23° and 30°. It is expected that further stable angles would occur with coarser crystals as found in temperate glaciers.

scholarly journals Ice-Fabric Study of the Mawson Region, East Antarctica

1969 ◽  
Vol 8 (53) ◽  
pp. 253-276 ◽  
Author(s):  
K. Kizaki
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Ice Sheet ◽  
Secondary Recrystallization ◽  
East Antarctica ◽  
Strain Rates ◽  
Fine Grained ◽  
Single Maximum ◽  
Multiple Maxima

Attempts are made to test the relation predicted by Brace (1960) between strain-rates and the ice-fabric patterns obtained at Mawson station, east Antarctica. These orientation fabrics not only are hardly related to the prediction by Brace (1960) or Kamb (1959) but also change easily within a strain grid with 100m diagonals.Stable patterns of two- and three-maximum fabrics are confirmed. The latter is common and stable in the coarse ice at the surface of the ice sheet. It is apparent that the fabric patterns are generally related to the grain-size. The single-maximum fabric always occurs in fine-grained ice, then more maxima are formed in the course of grain growth.It appears that syntectonic-secondary recrystallization is effective in producing the orientation fabrics with two, three and multiple maxima. Also, the maxima always shift away from the pole of foliation as grain-size increases and there are several stable positions of maximum such as 0°, 17°, 23° and 30°. It is expected that further stable angles would occur with coarser crystals as found in temperate glaciers.

scholarly journals Fabric Analysis of Surface Ice near Casey Range, East Antarctica

1969 ◽  
Vol 8 (54) ◽  
pp. 375-383 ◽  
Author(s):  
Koshiro Kizaki
Keyword(s):  
Strain Rate ◽  
Grain Growth ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Streams ◽  
Antarctic Ice Sheet ◽  
Single Maximum ◽  
Fabric Analysis ◽  
Surface Ice ◽  
The Antarctic

AbstractForbes Glacier, one of the outlet ice streams from the Antarctic ice sheet, is located 20 km west of Mawson, Mac.Robertson Land, east Antarctica. In the uppermost part of the glacier near Casey Range, the velocity at the centre of the glacier is 59 m year−1and the strain-rate at seven strain grids ranges from −6.7 to 6.7×10−3year−1on the surface of the glacier. The fabric types of this area are characterized by single-maximum and small-girdle fabrics. It is confirmed that the single-maximum fabric is an original pattern which changes gradually to a small girdle fabric about the maximum compressive axis in association with grain growth. The patterns predicted by Brace (1960) can be adapted to the small-girdle fabrics of this area.

scholarly journals Fabric Analysis of Surface Ice near Casey Range, East Antarctica

1969 ◽  
Vol 8 (54) ◽  
pp. 375-383
Author(s):  
Koshiro Kizaki
Keyword(s):  
Strain Rate ◽  
Grain Growth ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Streams ◽  
Antarctic Ice Sheet ◽  
Single Maximum ◽  
Fabric Analysis ◽  
Surface Ice ◽  
The Antarctic

AbstractForbes Glacier, one of the outlet ice streams from the Antarctic ice sheet, is located 20 km west of Mawson, Mac.Robertson Land, east Antarctica. In the uppermost part of the glacier near Casey Range, the velocity at the centre of the glacier is 59 m year−1 and the strain-rate at seven strain grids ranges from −6.7 to 6.7×10−3 year−1 on the surface of the glacier. The fabric types of this area are characterized by single-maximum and small-girdle fabrics. It is confirmed that the single-maximum fabric is an original pattern which changes gradually to a small girdle fabric about the maximum compressive axis in association with grain growth. The patterns predicted by Brace (1960) can be adapted to the small-girdle fabrics of this area.

scholarly journals Strain-Rate and Grain‒Size Effects in Ice

1987 ◽  
Vol 33 (115) ◽  
pp. 274-280 ◽  
Author(s):  
David M. Cole
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Transition Point ◽  
Boundary Migration ◽  
Peak Stress ◽  
Strain Rates ◽  
Thin Sections ◽  
Fine Grained ◽  
Lower Strain ◽  
Polycrystalline Ice

AbstractThis paper presents and discusses the results of constant deformation-rate tests on laboratory-prepared polycrystalline ice. Strain-rates ranged from 10−7to 10−1s−1, grain–size ranged from 1.5 to 5.8 mm, and the test temperature was −5°C.At strain-rates between 10−7and 10−3s−1, the stress-strain-rate relationship followed a power law with an exponent ofn= 4.3 calculated without regard to grain-size. However, a reversal in the grain-size effect was observed: below a transition point near 4 × 10−6s−1the peak stress increased with increasing grain-size, while above the transition point the peak stress decreased with increasing grain-size. This latter trend persisted to the highest strain-rates observed. At strain-rates above 10−3s−1the peak stress became independent of strain-rate.The unusual trends exhibited at the lower strain-rates are attributed to the influence of the grain-size on the balance of the operative deformation mechanisms. Dynamic recrystallization appears to intervene in the case of the finer-grained material and serves to lower the peak stress. At comparable strain-rates, however, the large-grained material still experiences internal micro-fracturing, and thin sections reveal extensive deformation in the grain-boundary regions that is quite unlike the appearance of the strain-induced boundary migration characteristic of the fine-grained material.

scholarly journals Recrystallization of ice enhances the creep and vulnerability to fracture of ice shelves 

2021 ◽  
Author(s):  
Meghana Ranganathan ◽  
Brent Minchew ◽  
Colin Meyer ◽  
Matej Pec
Keyword(s):  
Grain Size ◽  
Ice Sheet ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Model Parameters ◽  
Localized Deformation ◽  
Ice Shelves ◽  
Fine Grained ◽  
Initiation And Propagation ◽  
Rapid Deformation

<p>The initiation and propagation of fractures in floating regions of Antarctica has the potential to destabilize large regions of the ice sheet, leading to significant sea-level rise. While observations have shown rapid, localized deformation and damage in the margins of fast-flowing glaciers, there remain gaps in our understanding of how rapid deformation affects the creep and toughness of ice. Here we derive a model for dynamic recrystallization in ice and other rocks that includes a novel representation of migration recrystallization, which is absent from existing models but is likely to be dominant in warm areas undergoing rapid deformation within the ice sheet. We show that, in regions of elevated strain rate, grain sizes in ice may be larger than expected (~15 mm) due to migration recrystallization, a significant deviation from solid earth studies which find fine-grained rock in shear zones. This may imply that ice in shear margins deforms primarily by dislocation creep, suggesting a flow-law exponent of n=4 in these regions. Further, we find from existing models that this increase in grain size results in a decrease in tensile strength of ice by ~75% in the margins of glaciers. Thus, we expect that this increase in grain size makes the margins of fast-flowing glaciers less viscous and more vulnerable to fracture than we may suppose from standard model parameters.</p>

Effect of Silver on Superplastic Deformation in YBa2Cu3O7–x/Ag Composites

2002 ◽  
Vol 17 (5) ◽  
pp. 1172-1177
Author(s):  
Jondo Yun ◽  
Ye T. Chou ◽  
Martin P. Harmer
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Superplastic Deformation ◽  
Close Agreement ◽  
Silver Content ◽  
Strain Rates ◽  
Compression Tests ◽  
Fine Grained ◽  
Soft Inclusion ◽  
Activation Energy Of Deformation

Superplastic deformation was studied in fine-grained (0.7–1.1 μm) YBa2Cu3O7–x/Ag composites containing 2.5–25 vol% Ag. The compression tests were conducted in the temperature range of 750–875 °C and at strain rates of 10−5 to 10−3/s. For the YBa2Cu3O7−x/25%Ag composites with grain size of 0.7–1.1 μm, deformed at 800–850 °C and 10−5 to 10−3/s, the stress exponent, grain size exponent, and the activation energy of deformation were 2.0 ± 0.1, 2.5 ± 0.7, and 760 ± 100 kJ/mol, respectively. These values were the same as those of the pure YBa2Cu3O7−x, indicating that the deformation of the composite was controlled by that of the rigid YBa2Cu3O7−x phase. However, the strain rate was increased by the addition of silver as explained by the soft inclusion model of Chen. The dependence of the flow stress on the silver content was in close agreement with the prediction of the model.

Microstructural Evolution of Synthetic Forsterite Aggregates Deformed to High Strain

2004 ◽  
Vol 467-470 ◽  
pp. 579-584 ◽  
Author(s):  
A. Kellermann Slotemaker ◽  
J.H.P. de Bresser ◽  
C.J. Spiers ◽  
M.R. Drury
Keyword(s):  
Grain Size ◽  
Dynamic Recrystallization ◽  
Grain Growth ◽  
Microstructural Evolution ◽  
Large Scale ◽  
High Strain ◽  
Confining Pressure ◽  
Size Reduction ◽  
Coarse Grained ◽  
Fine Grained

Microstructures provide the crucial link between solid state flow of rock materials in the laboratory and large-scale tectonic processes in nature. In this context, microstructural evolution of olivine aggregates is of particular importance, since this material controls the flow of the Earth’s upper mantle and affects the dynamics of the outer Earth. From previous work it has become apparent that if olivine rocks are plastically deformed to high strain, substantial weakening may occur before steady state mechanical behaviour is approached. This weakening appears directly related to progressive modification of the grain size distribution through competing effects of dynamic recrystallization and syn-deformational grain growth. However, most of our understanding of these processes in olivine comes from tests on coarse-grained materials that show grain size reduction through dynamic recrystallization. In the present study we focused on fine-grained (~1 µm) olivine aggregates (i.e., forsterite/Mg2SiO4), containing ~0.5 wt% water and 10 vol% enstatite (MgSiO3), Samples were axially compressed to varying strains up to a maximum of ~45%, at 600 MPa confining pressure and a temperature of 950°C. Microstructures were characterized by analyzing full grain size distributions and textures using SEM/EBSD. We observed syndeformational grain growth rather than grain size reduction, and relate this to strain hardening seen in the stress-strain curves.

scholarly journals Seasonal changes in glacial polynya activity inferred from Weddell Sea varves

2013 ◽  
Vol 9 (5) ◽  
pp. 5123-5156 ◽  
Author(s):  
D. Sprenk ◽  
M. E. Weber ◽  
G. Kuhn ◽  
V. Wennrich ◽  
T. Hartmann ◽  
...  
Keyword(s):  
Grain Size ◽  
Bottom Water ◽  
Chemical Elements ◽  
Winter Season ◽  
Ice Sheet ◽  
Weddell Sea ◽  
Water Production ◽  
Thin Sections ◽  
Fine Grained ◽  
Coastal Polynya

Abstract. The Weddell Sea and the associated Filchner-Rønne Ice Shelf constitute key regions for global bottom-water production today. However, little is known about bottom-water production under different climate and ice-sheet conditions. Therefore, we studied core PS1795, which consists primarily of fine-grained siliciclastic varves that were deposited on contourite ridges in the southeastern Weddell Sea during the Last Glacial Maximum (LGM). We conducted high-resolution X-ray fluorescence (XRF) analysis and grain-size measurements with the RADIUS tool (Seelos and Sirocko, 2005) using thin sections to characterize the two seasonal components of the varves at sub-mm resolution to distinguish the seasonal components of the varves. Bright layers contain coarser grains that can mainly be identified as quartz in the medium to coarse silt grain size. They also contain higher amounts of Si, Zr, Ca, and Sr, as well as more ice-rafted debris (IRD). Dark layers, on the other hand, contain finer particles such as mica and clay minerals from the chlorite and illite groups. In addition, chemical elements, Fe, Ti, Rb, and K are elevated as well. Based on these findings as well as on previous analyses on neighbouring cores, we propose a model of glacially enhanced thermohaline convection in front of a grounded ice sheet that is supported by seasonally variable coastal polynya activity. Accordingly, katabatic (i.e. offshore blowing) winds removed sea ice from the ice edge, leading to coastal polynya formation. We suggest that glacial processes were similar to today with stronger katabatic winds and enhanced coastal polynya activity during the winter season. If this is correct, silty layers are likely glacial winter deposits, when brine rejection was increased, leading to enhanced bottom water formation and increased sediment transport. Vice versa, finer-grained clayey layers were then deposited during summer, when coastal polynya activity was likely reduced.

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