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



Kovaleva, Elizaveta, Kloetzli, Urs, Wheeler, John ORCID: 0000-0002-7576-4465 and Habler, Gerlinde
(2018) Mechanisms of strain accommodation in plastically-deformed zircon under simple shear deformation conditions during amphibolite-facies metamorphism. JOURNAL OF STRUCTURAL GEOLOGY, 107. pp. 12-24.

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Abstract

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 have <c> axis oriented parallel to the foliation plane, with the majority of deformed grains having <c> axis 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 <1¯10>{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 <1¯10>{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.

Item Type: Article
Uncontrolled Keywords: Zircon, Elastic anisotropy, Strain accommodation, Slip, Crystal-plastic deformation
Depositing User: Symplectic Admin
Date Deposited: 12 Jan 2018 15:02
Last Modified: 19 Jan 2023 06:45
DOI: 10.1016/j.jsg.2017.11.015
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3015963