Some garnet microstructures: an illustration of the potential of orientation maps and misorientation analysis in microstructural studies |
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| Institution: | 1. Department of Earth Sciences, Liverpool University, Liverpool L69 3BX, UK;2. Dipartimento di Mineralogia e Petrologia, Corso Garibaldi 37, 35137 Padova, Italy;3. Department of Geology, University of Leicester, Leicester LE1 7RH, UK;1. Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Straße 24–25, 14476, Potsdam–Golm, Germany;2. Münster Isotope Research Centre, Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstraße 24, 48149, Münster, Germany;3. Department of Geological Sciences, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa;4. Earth Dynamics Research Group, ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS), The Institute for Geoscience Research (TIGeR), School of Earth and Planetary Sciences, Curtin University, GPO Box U1987, WA, 6845, Australia;5. Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Str. 49b, D-50674, Köln, Germany;1. Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS)/GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney NSW 2109, Australia;2. Géosciences Environnement Toulouse (GET), CNRS, CNES, IRD, Université Toulouse III, 14 avenue E. Belin, 31400 Toulouse, France;3. Department of Geophysics, Division of Earth and Planetary Sciences, Kyoto University, Kyoto 606-8502, Japan;4. Institute for Earth Sciences (ISTE), University of Lausanne, UNIL Mouline, Géopolis, 1015 Lausanne, Switzerland;1. Department of Earth and Atmospheric Science, The City College of New York, 160 Convent Ave, New York, NY 10031, USA;2. Department of Geological Sciences, Brown University, Providence, RI 02912, USA;3. California Institute of Technology, MC 100-23, 1200 E. California Blvd, Pasadena, CA 91125, USA;4. Department of Geological Sciences, Jackson School of Geosciences, University of Texas, Austin, TX 78712, USA;1. GeoSoilEnviroCARS, Center for Advanced Radiation Sources, The University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637, USA;2. Unité Matériaux et Transformations, UMR 8207 – CNRS – Université de Lille-ENSCL-INRA Bat. C6, 59655 Villeneuve d''Ascq, France;3. Laboratoire de Géologie, UMR8538 – École Normale Supérieure, 24 rue Lhomond, 75005, Paris, France;1. School of Geography, Environment & Earth Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand;2. Department of Geology, University of Otago, P.O. Box 56, Dunedin, New Zealand |
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| Abstract: | The microstructures of two contrasting garnet grains are mapped using automated electron backscatter diffraction. In both cases there is a very strong crystallographic preferred orientation, with measurements clustered round a single dominant orientation. Each garnet grain is divided into domains with similar orientations, limited by boundaries with misorientations of 2° or more. In both samples most of misorientation angles measured across orientation domain boundaries are significantly lower than those measured between random pairs of orientation domains. One sample is a deformed garnet that shows considerable distortion within the domains. Lines of orientation measurements within domains and across domain boundaries show small circle dispersions around rational crystallographic axes. The domain boundaries are likely to be subgrain boundaries formed by dislocation creep and recovery. The second sample is a porphyroblast in which the domains have no internal distortion and the orientation domain boundaries have random misorientation axes. These boundaries probably formed by coalescence of originally separate garnets. We suggest that misorientations across these boundaries were reduced by physical relative rotations driven by boundary energy. The data illustrate the potential of orientation maps and misorientation analysis in microstructural studies of any crystalline material. |
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