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Anisotropy of oxygen diffusion in diopside

Abstract : 18O diffusion coefficients have been measured by nuclear reaction analysis (NRA) in Fe-free synthetic diopside single crystals along the three crystallographic directions and in Fe-bearing natural diopside single crystals along the c direction at room pressure in the range 1050-1370°C and under controlled oxygen partial pressure (10 -3-10 -12 atm). Diffusion along a and c crystallographic directions is one order of magnitude faster than along b direction. Diffusion along c in natural diopside is about two times faster than in the synthetic sample. The activation energy along b is 323±27 kJ mol -1 and diffusion is insensitive to oxygen fugacity. For a and c directions activation energies are around 250 kJ mol -1 and the diffusion coefficients are slightly dependent on fO 2 (≈ fO 20.04). We suggest that the observed diffusion anisotropy is related to the oxygen diffusion paths within the crystallographic structure that prefer the under-bonded O2 oxygen sites. We propose a single law to describe diffusion along the two fast crystallographic directions a and c in diopside for natural conditions close to the QFM buffer: log D a,c ( m2s-1)=-10.0±0.6-(259±15 kJ mol-1)/2.303 RT, and D b≪D a,c
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Jannick Ingrin, Laure Pacaud, Olivier Jaoul. Anisotropy of oxygen diffusion in diopside. EARTH AND PLANETARY SCIENCE LETTERS, 2001, 192, pp.347-361. ⟨10.1016/S0012-821X(01)00460-5⟩. ⟨insu-03642944⟩



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