Original paper
The estimation of NaSi-CaAl interdiffusion rates in peristerite by homogenization experiments
Baschek, Gabriele; Johannes, Wilhelm
European Journal of Mineralogy Volume 7 Number 2 (1995), p. 295 - 308
24 references
published: Mar 21, 1995
manuscript accepted: Nov 24, 1994
manuscript received: Mar 24, 1994
DOI: 10.1127/ejm/7/2/0295
Abstract
Abstract Average NaSi-CaAl interdiffusion coefficients (D̃) were determined for two peristerites from Steiermark (Austria) and Burma at 1 GPa, 800 and 900 °C, using an additional N2-H2O fluid phase with xH2O = 0.5,0.3,0.1, and 0.0, by means of the homogenization method. The results at 900 °C show that the D̃ values of both peristerites are a function of the N2-H2O fluid composition;. An increase in xH2O of 0.1 leads to an increase in the diffusion coefficient by a factor of 2.2. The estimated D̃ values of the different peristerites using the homogenization method (Grove et al, 1984) differ by more than one order of magnitude from each other at the same experimental conditions. These results can be explained by the weakness of the homogenization method for the estimation of diffusion data for plagioclases with respect to the determination of the homogenization time (th). The time th is usually measured by the change in lamellar microstructure of the experimental products in TEM photographs. In this study, corrections for the determination of th are proposed on the basis of calculated concentration curves for the peristerites as a function of diffusion time. With these corrections, nearly identical D̃ values for both peristerites are obtained
Keywords
peristerite • interdiffusion coefficients (D̃) • homogenization method • transmission electron microscopy