Microstructural evidence for the transition from dislocation creep to dislocation-accommodated grain boundary sliding in naturally deformed plagioclase |
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| Institution: | 1. Department of Geological Sciences, California State University Northridge, 18111 Nordhoff St, Northridge, CA 91330-8266, USA;2. Department of Earth, Environmental and Planetary Sciences, Brown University, Box 1846, 324 Brook St., Providence, RI 02912, USA;3. Department of Geology and Geophysics, University of Wyoming, 1000 E. University Ave., Dept. 3006, Laramie, WY 82071, USA;1. Univ. Grenoble Alpes, CNRS, IRD, G-INP, IGE, F-38000 Grenoble, France;2. ARC Center of Excellence for Core to Crust Fluid Systems (CCFS) and GEMOC, Department of Earth and Planetary Science, Macquarie University, NSW 2109, Australia;3. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK;4. Department of Earth and Ocean Sciences, School of Environmental Science, University of Liverpool, Liverpool L69 3GP, UK;5. Geosciences Montpellier, Université de Montpellier/CNRS, F-34095 Montpellier, France;1. Laboratory of Environmental Geology, Department of Earth Sciences, University of Dschang, P.O. Box 67, Dschang, Cameroon;2. Department of Earth Sciences, Faculty of Sciences, University of Maroua, P.O. Box 46, Maroua, Cameroon;3. Department of Geology & Geophysics, Indian Institute of Technology, Kharagpur, 721302, India;4. Ministry of Scientific Research and Innovation, DPSP/CCAR, P.O. Box 1457, Yaoundé, Cameroon;5. Laboratory of Geology, Higher Teacher Training College, University of Yaoundé I, P.O. Box 47, Yaoundé, Cameroon;6. CEREGE UMR7330 Aix–Marseille Université CNRS, 13545, Aix–en–provence, France;1. Department of Environmental Sciences, Basel University, Switzerland;2. Department of Geosciences, UiT the Arctic University of Norway, Norway;3. Institut des Sciences de la Terre d’Orléans (ISTO), Université d’Orléans, France;4. Department of Earth Sciences, Utrecht University, The Netherlands;1. Department of Geological Sciences, California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330-8266, USA;2. Department of Geology, Delehanty Hall, University of Vermont, 180 Colchester Ave., Burlington, VT 05405-1758, USA |
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| Abstract: | We use quantitative microstructural analysis including misorientation analysis based on electron backscatter diffraction (EBSD) data to investigate deformation mechanisms of naturally deformed plagioclase in an amphibolite gabbro mylonite. The sample is from lower oceanic crust exposed near the Southwest Indian Ridge, and it has a high ratio of recrystallized matrix grains to porphyroclasts. Microstructures preserved in porphyroclasts suggest that early deformation was achieved principally by dislocation creep with subgrain rotation recrystallization; recrystallized grain (average diameter ～8 μm) microstructures indicate that subsequent grain boundary sliding (GBS) was active in the continued deformation of the recrystallized matrix. The recrystallized matrix shows four-grain junctions, randomized misorientation axes, and a shift towards higher angles for neighbor-pair misorientations, all indicative of GBS. The matrix grains also exhibit a shape preferred orientation, a weak lattice preferred orientation consistent with slip on multiple slip systems, and intragrain microstructures indicative of dislocation movement. The combination of these microstructures suggest deformation by dislocation-accommodated GBS (DisGBS). Strain localization within the recrystallized matrix was promoted by a transition from grain size insensitive dislocation creep to grain size sensitive GBS, and sustained by the maintenance of a small grain size during superplasticity. |
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| Keywords: | Plagioclase Electron backscatter diffraction Grain boundary sliding DisGBS Lattice preferred orientation Misorientation analysis |
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