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Solid Earth An interactive open-access journal of the European Geosciences Union

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Solid Earth, 7, 355-366, 2016
http://www.solid-earth.net/7/355/2016/
doi:10.5194/se-7-355-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
08 Mar 2016
Strain localization in ultramylonitic marbles by simultaneous activation of dislocation motion and grain boundary sliding (Syros, Greece)
A. Rogowitz1,2, J. C. White3, and B. Grasemann1 1Department for Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
2Natural History Museum, Burgring 7, 1010 Vienna, Austria
3Department of Earth Sciences, University of New Brunswick, 3 Bailey Dr, Fredericton, NB E3B 5A3, Canada
Abstract. Extreme strain localization occurred in the centre of the cross-cutting element of a flanking structure in almost pure calcite marbles from Syros, Greece. At the maximum displacement of 120 cm along the cross-cutting element, evidence of grain size sensitive deformation mechanisms can be found in the ultramylonitic marbles, which are characterized by (1) an extremely small grain size ( ∼  3 µm), (2) grain boundary triple junctions with nearly 120° angles, (3) a weak crystallographic preferred orientation with very low texture index (J = 1.4), (4) a random misorientation angle distribution curve and (5) the presence of small cavities. Using transmission electron microscopy, a deformation sequence is observed comprising recrystallization dominantly by bulging, resulting in the development of the fine-grained ultramylonite followed by the development of a high dislocation density ( ∼  1013 m−2) with ongoing deformation of the fine-grained ultramylonite. The arrangement of dislocations in the extremely fine-grain-sized calcite differs from microstructures created by classical dislocation creep mediated by combined glide and thermally activated climb. Instead, it exhibits extensive glide and dislocation networks characteristic of recovery accommodated by cross-slip and network-assisted dislocation movement without formation of idealized subgrain walls. The enabling of grain boundary sliding to dislocation activity is deemed central to initiating and sustaining strain softening and is argued to be an important strain localization process in calcite rocks, even at a high strain rate ( ∼  10−9 s−1) and low temperature (300 °C).

Citation: Rogowitz, A., White, J. C., and Grasemann, B.: Strain localization in ultramylonitic marbles by simultaneous activation of dislocation motion and grain boundary sliding (Syros, Greece), Solid Earth, 7, 355-366, doi:10.5194/se-7-355-2016, 2016.
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This paper discusses the processes resulting in extreme strain localization (gamma up to 1000) in an almost pure calcite marble located in Syros, Greece. We observed grain size reduction by bulging recrystallization, followed by the simultaneous activation of grain boundary sliding and a dislocation motion in conditions (high differential stress, high strain rate, low temperature) in which brittle deformation rather than ductile flow might be suspected.
This paper discusses the processes resulting in extreme strain localization (gamma up to 1000)...
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