Self diffusion of network formers (silicon and oxygen) in naturally occurring basaltic liquid

• Published in: Geochimica et cosmochimica acta 1996-02, Vol.60 (3), p.405-413
• Main Authors: Lesher, C.E., Hervig, R.L., Tinker, D.
• Format: Article
• Language: English
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/0016-7037(95)00400-9

Self diffusion coefficients (D*) for silicon and oxygen in anhydrous basaltic liquid [O/(Si + Al) = 2.5] were measured at 1 and 2 GPa and temperatures between 1320 and 1600°C. Simple diffusion couples were composed of isotopically normal basaltic glass synthesized from chemical reagents mated to chemically identical glass enriched in 18O and 30Si. Concentrations of 18O and 30Si across the interfacial region of the couples were analyzed by ion microprobe. At 1 and 2 GPa, Do* is consistently larger than DSi* for a given diffusion couple, but only at the highest temperature (1600°C) is the difference outside the small uncertainties for the analytical measurements. At 1 GPa the self diffusivities for both Si and O are well-described by the Arrhenius relationship InD(Si.O)*=(−12.5±0.2)−(170000±2000)/RT, where T is temperature in K, R is the gas constant in J K−1 mole−1, and D* is expressed in m2 s−1. Self diffusion coefficients at 2 GPa are a factor of 1.5 greater and at 1400°C the activation volume (Va) is −6.7 cm3 mol−1. The similarity in self diffusion coefficients, small activation energies (