Al diffusion in quartz

Abstract

AbstractWe have measured Ti diffusion in quartz under dry 1-atm conditions. Experiments were performed using synthetic and naturalquartz and a TiO 2 powder source, with Ti profiles obtained by Rutherford Backscattering Spectrometry (RBS). Over thetemperature range 700–1150 °C, the following Arrhenius relation was obtained for diffusion parallel to (001):D Ti ¼ 7 10 −8 expð−273F12kJ mol −1 =RTÞm 2 sec −1 Similar diffusivities were obtained for both synthetic and natural quartz, and for a range of Ti source materials, including naturaltitanite powder and rutile–quartz single crystal diffusion couples. Although Ti diffusion appears slightly slower in the directionnormal to c, this difference is not great.Using these diffusion parameters, calculations indicate that distances over which diffusional alteration of Ti concentrations inquartz could occur in a million years would be on order of 500 μm at 800 °C, and ∼15 μm at 600 °C. The Arrhenius relation aboveshould be broadly applicable, and may find application in constraining metamorphic histories under conditions where the Ti-in-quartz geothermometer can be reasonably applied. This relation can also be used to constrain peak temperatures and coolinghistories from observations of exsolved rutile needles in quartz and the width of the Ti-depleted zone that develops around thegrowing needles. Finally, these findings may find utility in evaluating crystal residence times in magmatic systems when coupledwith observations of the sharpness of zoning patterns in quartz.© 2006 Elsevier B.V. All rights reserved.