Ti diffusion in quartz

doi:10.1016/j.chemgeo.2006.09.001

2007-01-01

227

PRE

D. J. Cherniak *

E. Bruce Watson

D. A. Wark

DOI：10.1016/j.chemgeo.2006.09.001

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摘要

En 中文

We have measured Ti diffusion in quartz under dry 1-atm conditions. Experiments were performed using synthetic and natural quartz and a TiO2 powder source, with Ti profiles obtained by Rutherford Backscattering Spectrometry (RBS). Over the temperature range 700-1150 degrees C, the following Arrhenius relation was obtained for diffusion parallel to (001): D-Ti = 7 x 10(-8)exp(-273 +/- 12kJ mol(-1)/RT)m(2)sec(-1) Similar diffusivities were obtained for both synthetic and natural quartz, and for a range of Ti source materials, including natural titanite powder and rutile-quartz single crystal diffusion couples. Although Ti diffusion appears slightly slower in the direction normal to c, this difference is not great. Using these diffusion parameters, calculations indicate that distances over which diffusional alteration of Ti concentrations in quartz could occur in a million years would be on order of 500 mu m at 800 degrees C, and similar to 15 pm at 600 degrees C. The Arrhenius relation above should 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 cooling histories from observations of exsolved rutile needles in quartz and the width of the Ti-depleted zone that develops around the growing needles. Finally, these findings may find utility in evaluating crystal residence times in magmatic systems when coupled with observations of the sharpness of zoning patterns in quartz. (c) 2006 Elsevier BY All rights reserved.

Keyword:

quartz

diffusion

titanium

RBS