Anisotropy of oxygen diffusion in diopside

• Published in: Earth and planetary science letters 2001, Vol.192 (3), p.347-361
• Main Authors: Ingrin, Jannick, Pacaud, Laure, Jaoul, Olivier
• Format: Article
• Language: English
• Subjects: cooling; diffusion; diopside; O-18/O-16; oxygen; Sciences of the Universe
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/S0012-821X(01)00460-5

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 ( m 2 s −1)=−10.0±0.6−(259±15 kJ mol −1)/2.303 RT, and D b≪D a,c