Other
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59.3697f&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 59, Issue 18, pp.3697-3705
Other
3
Scientific paper
Interphase boundary diffusion rates of oxygen and potassium in fine-grained K-feldspar/ quartz aggregates were determined experimentally at 450-700°C and 100 MPa (hydrothermal). The starting materials were hot-pressed and crystallized using equal weights of natural quartz fragments and orthoclase (KAlSi 3 O 8 ) composition glass. The technique employed isotopic tracers ( 18 O, 41 K) in an aqueous solution surrounding the sample, and depth profiling using an ion microprobe (SIMS). From the depth profiles, the product of the average boundary diffusion coefficient ( D ') and average effective boundary width ( ) was calculated using numerical solutions to the appropriate diffusion equation. Potassium and oxygen profiles measured in the same samples are different, confirming a diffusional transport mechanism. Potassium diffusion in the K-feldspar/quartz aggregate has a greater activation energy than oxygen (218 vs. 75 kJ/mol), and the Arrhenius relations cross at ~600°C. The D ' values in the K-feldspar/quartz aggregates are about a factor of four greater than both oxygen and potassium D ' values previously determined in monomineralic K-feldspar aggregates, and a factor of 20-40 greater than oxygen D ' values in monomineralic quartz aggregates. The Arrhenius relations show the activation energies for both oxygen and potassium are similar for the K-feldspar/quartz and monomineralic K-feldspar aggregates, and significantly lower for oxygen in K-feldspar/quartz versus monomineralic quartz aggregates.
Farver John R.
Yund Richard A.
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