Abstract
We studied the evolution of the microstructure of ice-Ih during static recrystallization by stepwise annealing experiments. We alternated thermal annealing and electron backscatter diffraction (EBSD) analyses on polycrystalline columnar ice pre-deformed in uniaxial compression at temperature of −7 °C to macroscopic strains of 3.0–5.2. Annealing experiments were carried out at −5 °C and −2 °C up to a maximum of 3.25 days, typically in 5–6 steps. EBSD crystal orientation maps obtained after each annealing step permit the description of microstructural changes. Decrease in average intragranular misorientation at the sample scale and modification of the misorientation across subgrain boundaries provide evidence for recovery from the earliest stages of annealing. This initial evolution is similar for all studied samples irrespective of their initial strain or annealing temperature. After an incubation period ≥1.5 h, recovery is accompanied by recrystallization (nucleation and grain boundary migration). Grain growth proceeds at the expense of domains with high intragranular misorientations, consuming first the most misorientated parts of primary grains. Grain growth kinetics fits the parabolic growth law with grain growth exponents in the range of 2.4–4.0. Deformation-induced tilt boundaries and kink bands may slow down grain boundary migration. They are stable features during early stages of static recrystallization, only erased by normal growth, which starts after >24 h of annealing.
Highlights
Unless exhumed rapidly due to tectonic processes, rocks deformed in the middle crust and deeper in the Earth remain at high temperature for extended time spans after the cessation of deformation
A close-up of the porphyroclasts reveals that in the outer part of the grains the misorientation gradients are spatially related to the sinuosity of grain boundaries, with subgrain boundaries often 'closing' a misorientated domain in a grain boundary bulge. This suggests that dynamic recrystallization in the present experiments involved grain boundary migration and nucleation and subgrain rotation
Stepwise static annealing experiments and coupled electron backscatter diffraction (EBSD) analyses of laboratory-made, pre-deformed polycrystalline columnar ice show that recovery starts at the earliest stages of annealing
Summary
Unless exhumed rapidly due to tectonic processes, rocks deformed in the middle crust and deeper in the Earth remain at high temperature for extended time spans after the cessation of deformation This results in annealing of the deformation microstructure by a series of thermally activated, diffusion-based processes, namely: recovery and static recrystallization, which may modify the crystal preferred orientation (CPO) or texture. Numerous studies have dealt with annealing phenomena in metals and alloys (see Humphreys and Hatherly, 2004 for a review) and in situ static recrystallization has been extensively studied in halite (Bestmann et al, 2005; Piazolo et al, 2006; Borthwick and Piazolo, 2010) Most of these studies focused on cubic materials, which due to their high symmetry have a large number of possible slip systems with similar strengths and, deform more homogeneously than most common minerals in the Earth crust and mantle. This behavior makes ice-Ih an excellent analogue material for silicate minerals that compose the Earth
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
