TY  - JOUR
A1  - Spallanzani, Roberta
A1  - Koga, Kenneth T.
A1  - Cichy, Sarah B.
A1  - Wiedenbeck, Michael
A1  - Schmidt, Burkhard C.
A1  - Oelze, Marcus
A1  - Wilke, Max
T1  - Lithium and boron diffusivity and isotopic fractionation in hydrated rhyolitic melts
T2  - Contributions to mineralogy and petrology
N2  - 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 degrees 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 x 10(-7) m(2)/s and 3.80 x 10(-8) m(2)/s, respectively.
Lithium isotopic fractionation during diffusion gave beta 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.
KW  - stable isotopes
KW  - diffusion
KW  - isotopic fractionation
KW  - hydrated silicate
KW  - melts
Y1  - 2022
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/64114
SN  - 0010-7999
SN  - 1432-0967
VL  - 177
IS  - 8
PB  - Springer
CY  - New York
ER  -