Hf-Zr interdiffusion in single crystal zircon

Abstract

Interdifrusivity of Hf and Zr in the zircon (ZrSiO4)-hafnon (HfSiO4) solid solution system was measured by (1) coupled annealing of synthetic hafnon and natural zircon and (2) heating of zircon crystal with a layer of hafnon epitaxially grown over the surface of zircon crystal. Because of the unexpectedly low diffusivity of Hf-Zr pair, practically usable value of diffusion coefficient was not obtained by the conventional coupled annealing technique. By use of the sample prepared by an epitaxial over-growth technique the upper limit of diffusion coefficient for Hf-Zr inter-diffusion in the zircon-hafnon system was found to be 5 1 x l(T15 cm2-sec-1at 1600°C. The observed low diffusivity of Hf-Zr pair in the zircon-hafnon system implies that diffusion of U, Th and radiogenic daughters does not affect lo age of zircon significantly during its residence in the parental magma, assum-ing that the diffusivities of those elements do not differ significantly from that observed for Hf-Zr. © 1992, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.