STRONTIUM DIFFUSION IN SANIDINE AND ALBITE, AND GENERAL COMMENTS ON STRONTIUM DIFFUSION IN ALKALI FELDSPARS

Abstract

Strontium chemical diffusion has been measured in albite and sanidine under dry, 1 atm, and QFM buffered conditions. Strontium oxide-aluminosilicate powdered sources were used to introduce the diffusant and Rutherford Backscattering Spectroscopy (RBS) used to measure diffusion profiles. For the 1 atm experiments, the following Arrhenius relations were obtained: Sanidine (Or61), temperature range 725-1075°C, diffusion normal to (001):D = 8.4 exp(-450 +/- 13 kJ mol-1/RT) m2s-1. Albite (Or1), temperature range 675-1025°C, diffusion normal to (001):D = 2.9 x 10-9 exp(-224 +/- 11 kJ mol-1/RT) m2s-1. The alkali feldspars in this and earlier work display a broad range of activation energies for Sr diffusion, which may be a consequence of the thermodynamic non-ideality of the alkali feldspar system and/or the mixed alkali effect.