Behaviour of Trace Elements at Shock Transformation of Zircon to Reidite

Large single crystals of natural zircon were shock-loaded at 13.6 and 51.3 GPa in planar geometry. No structural transformations are observed after the loading at 13.6 GPa. In the experiment at 51.3 GPa zircon transforms to its denser polymorph – reidite, with sheelite-like structure. Investigation of the reidite sample using -ray diffraction, Raman spectroscopy, photo- and cathodoluminescence revealed segregation of some trace elements cations (such as REE) on planar defects. Importantly, the segregation has occurred in a laboratory-scale experiment without long-term annealing of the sample after the shock loading. Plausible mechanism of segregation of three-valent trace elements implies local violation of charge balance in course of reconstructive transformation of zircon to reidite. As a result of related changes in topology of polyhedra and in second (Si–Zr) coordination sphere, a fraction of trace elements is expelled into energetically expensive interstitial positions with high diffusivities even at low temperatures.