Mathematics – Logic
Scientific paper
Jan 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978gecoa..42...45g&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 42, Issue 1, pp.45-57
Mathematics
Logic
37
Scientific paper
Self-diffusion of oxygen in adularia, anorthite, albite, oligoclase and labradorite has been measured by isotope exchange of oxygen between natural feldspars and hydrothermal water enriched in 18 O. The analysis consisted of measuring the 18 O/ 16 O gradient inward from the feldspar surface using an ion microprobe, and fitting a solution of the diffusion equation to the data. Depth of the sputtered hole was measured with an optical interferometer. Linear Arrhenius plots were obtained: The results for two intermediate plagioclases (Ab 82.5 and Ab 35.7 ) between 550 and 800°C are similar to these, and hence all the feldspars have very similar oxygen exchange behavior. Diffusion coefficients for albite at 800°C measured normal to the (001), (010), ( 11), and (130) faces are the same within a factor of four. Owing to the low activation energy, there is no single "closure temperature" for exchange of oxygen. The feldspars are susceptible to diffusional exchange of oxygen in geological settings to comparatively low temperatures.
Giletti Bruno J.
Semet Michel P.
Yund Richard A.
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