Diffusion of dissolved SiO2 in H2O at 1 GPa, with implications for mass transport in the crust and upper mantle

Article Abstract:

A research simulating geologic pressure and time (P-T) conditions were performed on SiO2 to elucidate the mechanisms of dissolved-solute diffusion in aqueous fluids. The extremely temperature-dependent solubility of quartz, together with the influence of high diffusivity for SiO2 at crustal conditions indicated that there may be substantial diffusive fluxes via an unmoving fluid in a normal geothermal gradient. The results also seem to support an inverse relationship between P-T viscosity and diffusion for SiO2.

Measurement, Viscosity, Rheology, Quartz, Metasomatism (Mineralogy), Metasomatism

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Magnesium self-diffusion in orthoenstatite

Article Abstract:

Research was conducted on three crystallographic directions in orhtoenstatite to determine its magnesium self-diffusion coefficients. A thin film approach was used to create the diffusion couples, while an ion microprobe was used to measure very short diffusional penetration profiles. Results showed a very small directional anisotropy for the self-diffusion of magnesium in the orthopyroxene at temperatures less than 1,000 degrees Centigrade.

Usage, Magnesium, Magnesium (Metal), Field ion microscope, Field ion microscopes

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Diffusion of tetravalent cations in zircon

Article Abstract:

Degrees of diffusion for three tetravalent cations U, Th and Hf were gauged in synthetic zircon using such diffusant sources as ground pre-synthesized silicates and oxide powders. Depth outlines were estimated by Rutherford backscattering spectrometry (RBS). Results indicated that diffusivity increases as the ionic radius decreases, confirming the findings of a previous study of rare earth diffusion in zircon.

Cations, Zircon

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