Fabrics of migmatites and the relationships between partial melting and deformation in high-grade transpressional shear zones: The Espinho Branco anatexite (Borborema Province,NE Brazil) |
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| Institution: | 1. Department of Earth Science, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan;2. Center for Northeast Asian Studies, Tohoku University, Aoba, Sendai 980-8576, Japan;3. Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan;1. Department of Geological Sciences, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa;2. Earth System Science Research Centre, Institute of Geoscience, University of Mainz, D-55099 Mainz, Germany |
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| Abstract: | The Espinho Branco anatexite, located within a transcurrent, high-temperature shear zone in NE Brazil, was the subject of a comprehensive petrostructural study (Anisotropy of Magnetic Susceptibility – AMS, Anisotropy of Anhysteretic Remanence – AAR, Electron Backscatter Diffraction – EBSD) to evaluate the compatibility of different fabrics with the kinematics of melt deformation. Magnetite dominates susceptibilities larger than 1 mSI and biotite displays 001] lattice directions consistent with AMS k3 axes. In contrast, migmatites with a susceptibility lower than 0.5 mSI and no visible mesoscopic foliation provide crystallographic fabrics distinct from AMS and AAR. However, AAR remains consistent with the regional strain field. These results suggest that the correlation of field, AMS and crystallographic fabrics is not always straightforward despite the relatively simple organisation of the magnetic fabric in the anatexite. We conclude that AMS recorded the final stages of the strain field in the migmatite irrespective of its complex mesoscale structures and contrasting crystallographic fabrics. |
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