Oxygen exchange experiments have been performed between single crystals of sanidine feldspar and water enriched in17O and180; temperatures were in the range 550-850 C and total pressure 1 kbar. Oxygen isotope diffusion profiles in a direction perpendicular to (001) were determined with an ion microprobe. The diffusion data for both isotopes followed a single Arrhenius relationship described by D = 3-95 x 10-12exp(-109-7 ±4kJmol-1/RT)m2s-1Combining concentration-distance data for17O and18O simultaneously for each profile in the form of a double ‘inverse error function plot’ enabled the ratio D17/D18)ls of diffusion coefficients to be obtained directly, and the isotope mass effect Eα βto be estimated. At 550 and 650°C Eα βvalues were in the range 0-85-1 -03, suggesting an interstitial mechanism for oxygen diffusion in sanidine feldspar, although the uncertainties (±0-10) do not preclude a vacancy mechanism. A methodology and mathematical analysis has been developed for isotope-mass-effect studies using infinite reservoir geometry, but the degree of precision attainable is limited by analytical techniques and procedures.
|Number of pages||19|
|Journal||Philosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties|
|Publication status||Published - 1 Feb 1997|