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| Titel |
Grain growth and experimental deformation of fine-grained ice aggregates |
| VerfasserIn |
Sabrina Diebold, Hans De Bresser, Chris Spiers, William B. Durham, Laura Stern |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041742
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| Zusammenfassung |
| Ice is one of the most abundant materials in our solar system. It is the principal constituent of
most of the moons of the outer solar system. Thus, the flow behavior of ice is of great interest
when studying geodynamic processes on icy moons. Grain growth is an elementary process
that is assumed to be important in the ice sheet layering of planetary moons, where
temperatures 100-273 K exist. We concentrate on the questions to what extent grain growth
may influence the evolution of strength of deforming ice and if the grain growth process is
independent or dependent of deformation. The answers to these questions will help us to
quantitatively test the hypothesis that the progressive evolution of the grain (crystal) size
distribution of deforming and recrystallizing ice directly affects its rheological
behaviour in terms of composite grain-size-sensitive (GSS) and grain-size-insensitive
(GSI) creep, and that this might, after time, result in a steady state balance between
mechanisms of GSS and GSI creep. We performed static grain growth experiments at
different temperatures and a pressure (P) of 1 atm, and deformation experiments at
P = 30-100 MPa starting in the GSS-creep field. The starting material ice Ih has
a grain size < 2 μm and was generated by a special pressure-release technique
described by Stern et al. (1997) resulting in dense ice aggregates. The ice grains of the
polycrystalline starting samples were randomly oriented and the material has a porosity of <
0.5%. For the grain growth tests a Hart Scientific temperature bath was filled with
d-Limonene as cooling medium. The ice specimens were put into sealed alumina
cylinders. For the grain growth tests, temperatures (T) between 213 K and 268 K were
chosen. The durations of these tests varied between one day and two weeks. For
the deformation experiments, temperatures of > 170 K and strain rates between
10-8 s-1 and 10-4 s-1 were chosen. Grain sizes, grain size distributions and grain
topologies were measured by cryogenic SEM and image analysis techniques. We found
clear evidence of grain growth and a significantly T-dependent variation of grain
size distributions. The observations allow us to calibrate values for the grain size
exponent n and the activation energy Q as used in conventional grain growth laws. We
simulated grain growth of ice based on the microphysical model of Kellermann
Slotemaker (2006). This model takes into account full grain size distributions and
allows grain boundary migration driven by different acting forces. We will show the
importance of these driving forces for grain growth and deformation in polycrystalline ice
aggregates.
References
Kellermann Slotemaker, A., 2006. Dynamic recrystallization and grain growth in olivine
rocks. PhD Thesis, Utrecht University, Utrecht, 187 pp.
Stern, L., 1997. Grain-size-inducedweakening of H2O ices I and II and associated
anisotropic recrystallization. Journal of Geophysical Research, 102 (B3): 5313-5325. |
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