Microstructures and Fabric Transitions of Natural Ice from the Styx Glacier, Northern Victoria Land, Antarctica
Abstract
:1. Introduction
2. Materials and Methods
2.1. Geological Outline and Sample Descriptions
2.2. Analytical Methods
3. Results
4. Discussion
4.1. Stress Regimes and CPO Development
4.2. Recrystallization Processes and Slip Systems
4.3. Origin of Extensional Stress Regime and Implications for Ice Sheet Dynamics
5. Conclusions
- With increasing depth, the analyzed samples show a systematic change from a weak single cluster of c-axes at 50 m, to a single cluster with weak multi-maxima between 80–110 m, and to a single cluster with a girdle between 140–170 m. An a-axis cluster occurs normal to the c-axis girdle. The formation of the girdle that accompanied the strong single cluster is characterized by an abrupt increase in fabric indices, and a decrease in the shape factor; thus, suggesting the extension began to occur at the depth of <140 m.
- Straight grain boundaries, relatively uniform grain size, triple junction of ~120°, and a weak single cluster of c-axes at 50 m (Figure 4 and Figure 6) are typically regarded as products of polygonization under compression, mainly due to bubble extraction. With an increased depth of burial, grain size increased, fabric strengthened, and the irregularity increased in grain shape (Figure 5 and Figure 6). At the depth of 140 m, highly curved grain shapes, abrupt increase of fabric indices, and the occurrence of a girdled c-axes (K < 1) suggest dynamic recrystallization dominated by GBM.
- The ice generally flows at ca. 2.3 m yr−1 from the northwest (NW) to the SE, dominated under the finite longitudinal and horizontal shear regimes. The presence of a nunatak located ~4 km far from the sample location in the SE direction, and a low surface velocity of ice, allowed the appearance of a girdle of c-axes between 140–170 m. The girdle was the result of an extensional stress regime generated at that depths. These results suggest the occurrence of changeable stress regimes as a response to diverse environments, such as an abrupt appearance of a small peak in the bedrock.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Sample Numbers | Location (Latitude, Longitude) | Depth (m) | Density (kg/m3) a | Age (kyr) b | Temperature (°C) c | Finite Longitudinal Strain d | Longitudinal Strain Rate (s−1) | Upper Bound Horizontal Shear Strain Rate (s−1) e | Lower Bound Horizontal Shear Strain Rate (s−1) f | Lower Bound Horizontal Shear Strain |
---|---|---|---|---|---|---|---|---|---|---|
SG_50 | Styx Glacier (73° 51′ 6.0″S, 163° 41′ 13.2″E) | 50.03–50.08 | 783 | 0.26 | −31.2 | 0.81 | 9.82 × 10−11 | 1.3 × 10−10 | 1.02 × 10−13 | 0.00 |
SG_80 | 79.97–80.02 | 884 | 0.55 | −30.8 | 0.93 | 5.34 × 10−11 | 5.10 × 10−13 | 0.01 | ||
SG_110 | 109.91–109.96 | 900 | 0.90 | −30.3 | 0.94 | 3.33 × 10−11 | 1.52 × 10−12 | 0.04 | ||
SG_140 | 140.47–140.52 | 917 | 1.31 | −29.8 | 0.96 | 2.33 × 10−11 | 3.49 × 10−12 | 0.14 | ||
SG_170 | 170.19–170.24 | 922 | 1.83 | −28.9 | 0.97 | 1.68 × 10−11 | 6.90 × 10−12 | 0.40 |
Sample Numbers | Step Size (μm) | Success Rate (%) a | Mean Grain Size with std. dev. (μm) | Fabric Strength | Seismic Anisotropy (%) | Number of Crystals | Number of Indexed Pixels | ||
---|---|---|---|---|---|---|---|---|---|
J-index | M-index | AVP | AVS | ||||||
SG_50 | 40 | 84.46 | 1240 ± 550 | 1.4618 | 0.0372 | 0.7 | 1.92 | 385 | 257,290 |
SG_80 | 40 | 93.46 | 1580 ± 970 | 1.9663 | 0.0725 | 1 | 2.68 | 242 | 349,756 |
SG_110 | 40 | 96.21 | 1790 ± 1200 | 2.1067 | 0.0853 | 0.7 | 2.07 | 185 | 373,586 |
SG_140 | 40 | 93.12 | 2000 ± 1280 | 5.0772 | 0.3009 | 2.8 | 6.87 | 101 | 159,714 |
SG_170 | 40 | 97.40 | 2060 ± 1400 | 4.2485 | 0.2327 | 2.2 | 5.77 | 129 | 343,550 |
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Kim, D.; Prior, D.J.; Han, Y.; Qi, C.; Han, H.; Ju, H.T. Microstructures and Fabric Transitions of Natural Ice from the Styx Glacier, Northern Victoria Land, Antarctica. Minerals 2020, 10, 892. https://doi.org/10.3390/min10100892
Kim D, Prior DJ, Han Y, Qi C, Han H, Ju HT. Microstructures and Fabric Transitions of Natural Ice from the Styx Glacier, Northern Victoria Land, Antarctica. Minerals. 2020; 10(10):892. https://doi.org/10.3390/min10100892
Chicago/Turabian StyleKim, Daeyeong, David J. Prior, Yeongcheol Han, Chao Qi, Hyangsun Han, and Hyeon Tae Ju. 2020. "Microstructures and Fabric Transitions of Natural Ice from the Styx Glacier, Northern Victoria Land, Antarctica" Minerals 10, no. 10: 892. https://doi.org/10.3390/min10100892
APA StyleKim, D., Prior, D. J., Han, Y., Qi, C., Han, H., & Ju, H. T. (2020). Microstructures and Fabric Transitions of Natural Ice from the Styx Glacier, Northern Victoria Land, Antarctica. Minerals, 10(10), 892. https://doi.org/10.3390/min10100892