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High-temperature diffusion of oxygen in synthetic diopside measured by nuclear reaction analysis

Published online by Cambridge University Press:  05 July 2018

L. Pacaud
Affiliation:
Laboratoire d'étude des mécanismes de transfert en géologie, UMR CNRS 5563. Minéralogie, 39 allées Jules Guesde, F-31000 Toulouse, France
J. Ingrin
Affiliation:
Laboratoire d'étude des mécanismes de transfert en géologie, UMR CNRS 5563. Minéralogie, 39 allées Jules Guesde, F-31000 Toulouse, France
O. Jaoul
Affiliation:
Laboratoire d'étude des mécanismes de transfert en géologie, UMR CNRS 5563. Minéralogie, 39 allées Jules Guesde, F-31000 Toulouse, France

Abstract

We have performed O self-diffusion experiments in synthetic diopside single crystals along the b-axis at temperatures ranging from 1473–1643 K, under controlled O partial pressure (10−11–10−2 atm). The 18O tracer diffusion was imposed by solid/gas exchange between 16O in diopside and 18O2-enriched argon-hydrogen-H2O gas mixture. Diffusion profiles of 18O were measured by Nuclear Reaction Analysis 18O (p,α) 15N. The diffusion coefficients are described by , with log D0(m2/s)=−9.2 ± 1.0 and E 310 ± 30 kJ/mol.

Our results are in agreement with Ryerson and McKeegan's (1994) data and Farver's (1989) data along a direction perpendicular to the c direction. Experiments performed in a wide pO2 range show that D is independent of pO2.

We observe no change in the diffusion regime up to 1643 K (i.e. 22 K prior to melting temperature). This result differs from the diffusion study of Ca in diopside by Dimanov and Ingrin (1995), where a strong enhancement of Ca mobility, attributed to an excess disorder in the Ca-sublattice, was observed above 1523 K. We conclude that O diffusion in diopside is not affected by this premelting phenomenon.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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