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Journal Article

Lithium and boron diffusivity and isotopic fractionation in hydrated rhyolitic melts

Authors

Spallanzani,  Roberta
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

Koga,  Kenneth T.
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

/persons/resource/cichy

Cichy,  Sarah Bettina
3.6 Chemistry and Physics of Earth Materials, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

/persons/resource/michawi

Wiedenbeck,  Michael
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

Schmidt,  Burkhard C.
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

Oelze,  Marcus
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

Wilke,  Max
External Organizations;
GFZ SIMS Publications, Deutsches GeoForschungsZentrum;

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5013063.pdf
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Citation

Spallanzani, R., Koga, K. T., Cichy, S. B., Wiedenbeck, M., Schmidt, B. C., Oelze, M., Wilke, M. (2022): Lithium and boron diffusivity and isotopic fractionation in hydrated rhyolitic melts. - Contributions to Mineralogy and Petrology, 177, 74.
https://doi.org/10.1007/s00410-022-01937-2


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5013063
Abstract
Lithium and boron are trace components of magmas, released during exsolution of a gas phase during volcanic activity. In this study, we determine the diffusivity and isotopic fractionation of Li and B in hydrous silicate melts. Two glasses were synthesized with the same rhyolitic composition (4.2 wt% water), having different Li and B contents; these were studied in diffusion-couple experiments that were performed using an internally heated pressure vessel, operated at 300 MPa in the temperature range 700–1250 °C for durations from 0 s to 24 h. From this we determined activation energies for Li and B diffusion of 57 ± 4 kJ/mol and 152 ± 15 kJ/mol with pre-exponential factors of 1.53 × 10–7 m2/s and 3.80 × 10–8 m2/s, respectively. Lithium isotopic fractionation during diffusion gave β values between 0.15 and 0.20, whereas B showed no clear isotopic fractionation. Our Li diffusivities and isotopic fractionation results differ somewhat from earlier published values, but overall confirm that Li diffusivity increases with water content. Our results on B diffusion show that similarly to Li, B mobility increases in the presence of water. By applying the Eyring relation, we confirm that B diffusivity is limited by viscous flow in silicate melts. Our results on Li and B diffusion present a new tool for understanding degassing-related processes, offering a potential geospeedometer to measure volcanic ascent rates.