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Microstructural Evidence for Grain Boundary Migration and Dynamic Recrystallization in Experimentally Deformed Forsterite Aggregates

1
Bayerisches Geoinstitut, Universität Bayreuth, D-95445 Bayreuth, Germany
2
Department of Earth and Planetary Sciences, Washington University in Saint Louis, Saint Louis, MO 63117, USA
3
University of Lille, CNRS, INRA, ENSCL, UMR 8207-UMET-Unité Matériaux et Transformations, F-59000 Lille, France
4
Institute of Physical Metallurgy and Metal Physics, RWTH Aachen University, 52074 Aachen, Germany
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(1), 17; https://doi.org/10.3390/min9010017
Received: 21 October 2018 / Revised: 27 November 2018 / Accepted: 21 December 2018 / Published: 27 December 2018
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Abstract

Plastic deformation of peridotites in the mantle involves large strains. Orthorhombic olivine does not have enough slip systems to satisfy the von Mises criterion, leading to strong hardening when polycrystals are deformed at rather low temperatures (i.e., below 1200 °C). In this study, we focused on the recovery mechanisms involving grain boundaries and recrystallization. We investigated forsterite samples deformed at large strains at 1100 °C. The deformed microstructures were characterized by transmission electron microscopy using orientation mapping techniques (ACOM-TEM). With this technique, we increased the spatial resolution of characterization compared to standard electron backscatter diffraction (EBSD) maps to further decipher the microstructures at nanoscale. After a plastic strain of 25%, we found pervasive evidence for serrated grain and subgrain boundaries. We interpreted these microstructural features as evidence of occurrences of grain boundary migration mechanisms. Evaluating the driving forces for grain/subgrain boundary motion, we found that the surface tension driving forces were often greater than the strain energy driving force. At larger strains (40%), we found pervasive evidence for discontinuous dynamic recrystallization (dDRX), with nucleation of new grains at grain boundaries. The observations reveal that subgrain migration and grain boundary bulging contribute to the nucleation of new grains. These mechanisms are probably critical to allow peridotitic rocks to achieve large strains under a steady-state regime in the lithospheric mantle. View Full-Text
Keywords: olivine; plastic deformation; ACOM-TEM; grain boundary migration; recrystallization; recovery olivine; plastic deformation; ACOM-TEM; grain boundary migration; recrystallization; recovery
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Bollinger, C.; Nzogang, B.C.; Mussi, A.; Bouquerel, J.; Molodov, D.A.; Cordier, P. Microstructural Evidence for Grain Boundary Migration and Dynamic Recrystallization in Experimentally Deformed Forsterite Aggregates. Minerals 2019, 9, 17.

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