• Mechanisms of strain accommodation in plastically-deformed zircon under simple shear deformation conditions during amphibolite-facies metamorphism

    • Elizaveta Kovaleva
      Department of Lithospheric Research, Faculty of Earth Sciences, Geography and Astronomy, University of Vienna
    • Urs Klötzli
      Department of Lithospheric Research, Faculty of Earth Sciences, Geography and Astronomy, University of Vienna
    • John Wheeler
      Department of Earth, Ocean and Ecological Sciences, University of Liverpool
    • Gerlinde Habler
      Department of Lithospheric Research, Faculty of Earth Sciences, Geography and Astronomy, University of Vienna
  • This study documents the strain accommodation mechanisms in zircon under amphibolite-facies metamorphic conditions in simple shear. Microstructural data from undeformed, fractured and crystal-plastically deformed zircon crystals are described in the context of the host shear zone, and evaluated in the light of zircon elastic anisotropy. Our work challenges the existing model of zircon evolution and shows previously undescribed rheological characteristics for this important accessory mineral. Crystal-plastically deformed zircon grains haveaxis oriented parallel to the foliation plane, with the majority of deformed grains havingaxis parallel to the lineation. Zircon accommodates strain by a network of stepped low-angle boundaries, formed by switching between tilt dislocations with the slip systems<100>{010} and<110>{110} and rotation axis [001], twist dislocations with the rotation axis [001], and tilt dislocations with the slip system<100>{001} and rotation axis [010]. The slip system<110>{110} is newly described for zircon. Most misorientation axes in plastically-deformed zircon grains are parallel to the XY plane of the sample and have [001] crystallographic direction. Such behaviour of strained zircon lattice is caused by elastic anisotropy that has a direct geometric control on the rheology, deformation mechanisms and dominant slip systems in zircon. Young's modulus and P wave velocity have highest values parallel to zircon [001] axis, indicating that zircon is elastically strong along this direction. Poisson ratio and Shear modulus demonstrate that zircon is also most resistant to shearing along [001]. Thus, [001] axis is the most common rotation axis in zircon. The described zircon behaviour is important to take into account during structural and geochronological investigations of (poly)metamorphic terrains. Geometry of dislocations in zircon may help reconstructing the geometry of the host shear zone(s), large-scale stresses in the crust, and, possibly, the timing of deformation, if the isotopic systems of deformed zircon were reset.

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  • http://phaidra.univie.ac.at/o:923763

  • Article

  • Accepted Version

  • 2018

  • 107

  • 12-24

  • Elsevier BV

  • English

  • Embargoed access

  • 02.12.2019

  • I471-N19 – Austrian Science Fund (FWF)

  • 0191-8141

  • crystal-plastic deformation; slip; strain accomodation; elastic anisotropy; Zircon

  • Dewey Decimal Classification → Science → Earth sciences & geology → Earth sciences