Role of Elastic Anisotropy in the Development of Deformation Microstructures in Zircon

he deformation of zircon by various mechanisms, including brittle fracture, dislocation creep, twinning, and transformation to a high-pressure polymorph (reidite), is preceded by elastic behavior. This study presents new visualizations of the anisotropy of elastic properties of zircon as a function of radiation damage and pressure, and investigates the links between elastic properties and deformation microstructures in zircon. Zircon is highly anisotropic in Young's modulus (E), shear modulus (G), and Poisson's ratio (ν) elasticity. Anisotropy of E, G, and ν decreases by radiation damage and increases with pressure from 0 to 24 GPa, with a peak in elastic stiffness at ~8 GPa. A switch in dislocation line energy factor K could indicate that (001)<100>dislocations are energetically more favorable than {100}<010> above ~17 GPa. Shock twinning of zircon occurs via plane of invariant shear K 1 = {112} and shear direction η 1 = <111>, which corresponds to the lowest values of G <111> (~98 GPa) and ν(≈0) in zircon. Minima in G <111> at ~4 and ~16 GPa could indicate favorable pressures for twinning. Reduction of E and G associated with radiation damage inhibits propagation of reidite lamellae during shock metamorphism because sufficient pressures to permit phase transformation cannot be supported.