Self diffusion of Si and O in dacitic liquid at high pressures
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David Tinker
und
Charles E. Lesher
Abstract
Laboratory experiments have been conducted to determine simultaneously the self diffusivities of Si and O in synthetic dacite melt (NBO/T = 0.1) from 1 to 5.7 GPa and from 1355 to 1662 °C. Glasses enriched in 18O and 28Si were synthesized and mated to their isotopically normal counterparts to form diffusion couples used in the piston cylinder device (1 and 2 GPa) and multi-anvil apparatus (4 to 5.7 GPa). Profiles of isotope abundances were measured by secondary ion mass spectrometry. Self-diffusion coefficients for Si (D*Si) are significantly lower than self-diffusion coefficients for O (D*0) at all run conditions; for example, D*0 = 6.45 ± 0.65 × 10-14 m2/s and D*Si = 1.45 ± 0.45 × 10-14 m2/s at 1 GPa and 1355 °C. The temperature dependence is similar, but not identical, for Si and O self diffusion at all pressures, yielding activation energies of 293-380 kJ/mol at 1 GPa, 264-305 kJ/mol at 2 GPa, and 155-163 kJ/mol at 4 GPa. The pressure dependence is similar for Si and O at all temperatures, giving activation volumes for Si and O that are -14.5 to -17.1 cm3/mol at 1460 °C, -9.8 to -8.7 cm3/mol at 1561 °C, and -8.8 to -9.3 cm3/mol at 1662 °C. Self-diffusion coefficients for Si and O reach maximum values at roughly 5 GPa. The mode of Si and O self diffusion in dacitic liquids is constrained by the large activation volumes, D*0 ≈ 2 D*Si, and predictions using the Eyring equation, which suggest that Si and O diffuse as molecular species at 1460 °C. At 1561 and 1662 °C, less negative activation volumes and predictions of the Eyring equation are consistent with diffusion of Si and O by a combination of mechanisms, including the formation of a high-coordinated intermediate species.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Self diffusion of Si and O in dacitic liquid at high pressures
- The effect of anhydrous composition on water solubility in granitic melts
- Stability and phase relations of Ca[ZnSi3]O8, a new phase with feldspar structure in the system CaO-ZnO-SiO2
- Magmatic Na-rich phlogopite in a suite of gabbroic crustal xenoliths from Volcán San Pedro, Chilean Andes: Evidence for a solvus relation between phlogopite and aspidolite
- The influence of T, aSiO₂, and fO₂ on exsolution textures in Fe-Mg olivine: An example from augite syenites of the Ilimaussaq Intrusion, South Greenland
- An experimental study of the external reduction of olivine single crystals
- Determination of site population in olivine: Warnings on X-ray data treatment and refinement
- Structural properties of ferromagnesian cordierites
- A calorimetric study of zoisite and clinozoisite solid solutions
- Mineralogy of lead in a soil developed on a Pb-mineralized sandstone (Largentière, France)
- Experimental mixtures of smectite and rectorite: Re-investigation of “fundamental particles” and “interparticle diffraction”
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