Intragranular dynamic recrystallization in naturally deformed calcite marble: diffusion accommodated grain boundary sliding as a result of subgrain rotation recrystallization |
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| Institution: | 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;1. Experimental Rock Deformation Laboratory, Department of Earth Sciences, Indian Institute of Technology Kanpur, Uttar Pradesh, 208 016, India;2. Department of Geological Sciences, Jadavpur University, West Bengal, 700 054, India;1. Steinmann Institute of the University Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany;2. GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany;3. Institute of Geosciences of the University of Kiel, Otto-Hahn-Platz 1, 24118 Kiel, Germany;4. Bayerisches Geoinstitut of the University Bayreuth, Germany |
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| Abstract: | Intragranular microshear zones within a greenschist facies calcite marble were studied to try to constrain better the processes of dynamic recrystallization as well as the deformation processes that occur within newly recrystallized grains. Intragranular recrystallized grains within large, twinned calcite porphyroclasts can be related to the host from which they have recrystallized and are the focus of an electron backscatter diffraction study. Lattice distortions, low angle boundaries and some high angle boundaries (>15°) in the microshears within a porphyroclast have the same misorientation axes suggesting that deformation occurred by climb-accommodated dislocation creep involving subgrain rotation recrystallization. Changes in the ratio of host and twin domain, as the deformation zone is entered, show that twin boundary migration also occurred. Recrystallized grains have similar sizes (10–60 μm) to subgrains, suggesting that they formed by subgrain rotation. However, within the intragranular microshear zones the misorientations between recrystallized grains and porphyroclasts are considerably larger than 15° and misorientation axes are randomly oriented. Moreover recrystallized grain orientations average around the porphyroclast orientation. We suggest that the recrystallized grains, once formed, are able to deform partly by diffusion accommodated grain boundary sliding, which is consistent with predictions made from lab flow laws. |
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