• Localization of submicron inclusion re-equilibration at healed fractures in host garnet

    • T. A. Griffiths
      Department für Lithosphärenforschung, Fakultät für Geowissenschaften, Geographie und Astronomie, Universität Wien
    • G. Habler
      Department für Lithosphärenforschung, Fakultät für Geowissenschaften, Geographie und Astronomie, Universität Wien
    • D. Rhede
      GFZ Potsdam
    • R. Wirth
      GFZ Potsdam
    • F. Ram
      Max-Planck-Institut für Eisenforschung
    • R. Abart
      Department für Lithosphärenforschung, Fakultät für Geowissenschaften, Geographie und Astronomie, Universität Wien
  • Microstructures in Permian inclusion-bearing meta-pegmatite garnets from the Koralpe (Eastern Alps, Austria) reveal re-equilibration by coarsening of abundant submicron-sized inclusions (1 µm – 2 nm diameter) at the site of healed brittle cracks. The microstructures developed during Cretaceous eclogite facies deformation and the related overprinting of the host-inclusion system. Trails of coarsened inclusions (1 – 10 µm diameter) crosscut the garnet, defining traces of former fractures with occasional en-echelon overlaps. Trails are flanked by 10 – 100 µm wide ‘bleaching zones’ characterized by the absence of ≤1 µm sized inclusions in optical and SE images. FEG-microprobe data show that trails and bleaching zones can form isochemically, although some trails exhibit non-isochemical coarsening. Cross correlation EBSD reveals subtle garnet lattice rotation of up to 0.45° around consistent misorientation axes, spatially correlated with bleaching zones. Elevated dislocation density within these zones is confirmed by TEM observations. Brittle fracture enhanced diffusion rates in the lattice adjacent to crack planes, priming these areas to behave differently to the bulk of the garnet during Cretaceous metamorphism and facilitating localized coarsening of inclusions. The preferred mechanism for this is increased dislocation density near former cracks, with the dislocations interpreted as a plastic wake originating from crystal plastic deformation at the crack tip. This partially closed host-inclusion system clearly records the influence of deformation mechanisms on re-equilibration and contributes to a wider understanding of the interaction between deformation and chemical reaction during metamorphism.

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  • http://phaidra.univie.ac.at/o:397967

  • Wissenschaftlicher Artikel

  • Angenommene Version

  • 2014

  • 168

  • 6

  • 1-21

  • Springer Science + Business Media

  • Englisch

  • Frei zugänglich

  • 15.11.2015

  • I471-N19 – Fonds zur Förderung der wissenschaftlichen Forschung (FWF)

  • 0010-7999

  • Diffusion; EBSD; Garnet; Inclusions; Fracturing; Re-equilibration

  • Dewey Dezimal Klassifikation → Naturwissenschaften und Mathematik → Geowissenschaften, Geologie → Petrology