Anisotropy of oxygen diffusion in diopside

Jannick Ingrin , Laure Pacaud , Olivier Jaoul

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 ₂^0.04). 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

Domains: Sciences of the Universe [physics]

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⟩