TY - JOUR

T1 - CO2 diffusion in dry and hydrous leucititic melt

AU - Koch, Lennart

AU - Schmidt, Burkhard C.

N1 - Publisher Copyright: © 2023 Lennart Koch.

PY - 2023/2/27

Y1 - 2023/2/27

N2 - Using the diffusion couple technique, diffusion of CO2 in a leucititic melt from the Colli Albani Volcanic District in Italy was investigated at temperatures between 1200 and 1350gg C in an internally heated pressure vessel at 300gMPa. To examine the effect of dissolved H2O in the melt, experiments were performed for a nominally dry melt (0.18±g0.03gwtg% H2O) and for a hydrous melt containing 3.36±g0.28gwtg% H2O. Diffusion experiments were run for 40 to 120gmin and terminated by rapid quench. CO2 concentration profiles were subsequently measured via attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and fitted with error functions to obtain individual diffusion coefficients. For the anhydrous and hydrous sample series, seven diffusion coefficients were determined each. Diffusivity was found to increase exponentially with temperature for both melts following an Arrhenius behaviour. The Arrhenius equation for the nominally dry leucititic melt is described by (Formula present), where DCO2 is the diffusion coefficient ingm2gs-1 and T is the temperature in K. In the experimental temperature range, H2O has an accelerating effect on CO2 diffusion. At 1200gg C, diffusivity increases from 1.94g×g10-12gm2gs-1 in the dry melt to 1.54g×g10-11gm2gs-1 in the hydrous melt. The Arrhenius equation for the leucititic melt containing 3.36±0.28gwtg% H2O is given by (Formula present). The activation energies for CO2 were determined to be 275±g47gkJgmol-1 for the anhydrous melt and 209±g58gkJgmol-1 for the hydrous melt. The high CO2 activation energy in the leucititic melt indicates that the diffusion might be partly attributed to the carbonate species. At high magmatic temperatures above 1200gg C, CO2 diffusivity in the leucititic melt is only slightly lower than CO2 diffusion in rhyolitic and basaltic melts, suggesting that CO2 diffusion in natural melts is relatively independent from the bulk melt composition at such temperatures. CO2 diffuses slower than other volatile components such as halogens and H2O in depolymerized silicate melts. Thus, a fractionation of volatiles can occur during magma ascent and degassing. The experimental data on CO2 diffusion can be used for modelling the degassing mechanisms of ultrapotassic mafic melts.

AB - Using the diffusion couple technique, diffusion of CO2 in a leucititic melt from the Colli Albani Volcanic District in Italy was investigated at temperatures between 1200 and 1350gg C in an internally heated pressure vessel at 300gMPa. To examine the effect of dissolved H2O in the melt, experiments were performed for a nominally dry melt (0.18±g0.03gwtg% H2O) and for a hydrous melt containing 3.36±g0.28gwtg% H2O. Diffusion experiments were run for 40 to 120gmin and terminated by rapid quench. CO2 concentration profiles were subsequently measured via attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and fitted with error functions to obtain individual diffusion coefficients. For the anhydrous and hydrous sample series, seven diffusion coefficients were determined each. Diffusivity was found to increase exponentially with temperature for both melts following an Arrhenius behaviour. The Arrhenius equation for the nominally dry leucititic melt is described by (Formula present), where DCO2 is the diffusion coefficient ingm2gs-1 and T is the temperature in K. In the experimental temperature range, H2O has an accelerating effect on CO2 diffusion. At 1200gg C, diffusivity increases from 1.94g×g10-12gm2gs-1 in the dry melt to 1.54g×g10-11gm2gs-1 in the hydrous melt. The Arrhenius equation for the leucititic melt containing 3.36±0.28gwtg% H2O is given by (Formula present). The activation energies for CO2 were determined to be 275±g47gkJgmol-1 for the anhydrous melt and 209±g58gkJgmol-1 for the hydrous melt. The high CO2 activation energy in the leucititic melt indicates that the diffusion might be partly attributed to the carbonate species. At high magmatic temperatures above 1200gg C, CO2 diffusivity in the leucititic melt is only slightly lower than CO2 diffusion in rhyolitic and basaltic melts, suggesting that CO2 diffusion in natural melts is relatively independent from the bulk melt composition at such temperatures. CO2 diffuses slower than other volatile components such as halogens and H2O in depolymerized silicate melts. Thus, a fractionation of volatiles can occur during magma ascent and degassing. The experimental data on CO2 diffusion can be used for modelling the degassing mechanisms of ultrapotassic mafic melts.

UR - http://www.scopus.com/inward/record.url?scp=85149437582&partnerID=8YFLogxK

U2 - 10.5194/ejm-35-117-2023

DO - 10.5194/ejm-35-117-2023

M3 - Article

VL - 35

SP - 117

EP - 132

JO - European Journal of Mineralogy

JF - European Journal of Mineralogy

SN - 1617-4011

IS - 1

ER -