Details
| Original language | English |
|---|---|
| Pages (from-to) | 243-262 |
| Number of pages | 20 |
| Journal | Chemical geology |
| Volume | 169 |
| Issue number | 1-2 |
| Early online date | 7 Aug 2000 |
| Publication status | Published - 15 Aug 2000 |
Abstract
H2O diffusion plays a major role in bubble growth and volcanic eruption. We report a comprehensive study of H2O diffusion in rhyolitic melts and glasses. This new study and previous investigations together cover a wide range of conditions: 400-1200°C, 0.1-810 MPa, and 0.1-7.7 wt.% total H2O content (H2O). In order to constrain how the diffusivity depends on H2O(t), both the diffusion-couple experiments and the dehydration experiments are carried out in a cold-seal vessel (CSV), an internally heated pressure vessel, and a piston cylinder. H2O concentration profiles are measured by infrared (IR) spectroscopy. Although there are still some experimental and analytical difficulties, our data represent a major improvement over earlier data. The diffusion data have been used to quantify H2O diffusivity as a function of temperature, pressure, and H2O(t). Assuming that molecular H2O (H2O(m)) is the diffusing species, the H2O(m) diffusivity (in μm2/s) can be expressed as: D(H(2)O(m)) = exp[(14.08 - 13,128/T - 2.796 P/T) + (-27.21 + 36,892/T + 57.23 P/T)X], where T is in Kelvin, P is in mPa, and X is the mole fraction of H2O(t) on a single oxygen basis. The pressure dependence is not so well-resolved compared to the dependence on T and X. The dependence of D(H(2)O(m)) on X increases with increasing pressure. The results are consistent with the data of Nowak and Behrens (1997) [Nowak, M., Behrens, H., 1997. An experimental investigation on diffusion of water in haplogranitic melts. Contrib. Mineral. Petrol. 126, 365-376.], but different from the assumption of Zhang et al. (1991a) [Zhang, Y., Stolper, E.M., Wasserburg, G.J., 1991a. Diffusion of water in rhyolitic glasses. Geochim. Cosmochim. Acta 55, 441-456.], because the dependence cannot be resolved from their low-H2O(t) diffusion data, and because the dependence is not so strong at low pressures. The activation energy for H2O(m) diffusion decreases as H2O(t) increases and depends on P (increases with P at X <0.05 and decreases with P at X > 0.05). The results roughly reconcile the different activation energies of Zhang et al. (1991a) and Nowak and Behrens (1997). The total (or bulk) H2O diffusivity (D(H2O(t)) can be calculated from D(H2O(t)) = D(H2O(m)) dX(m)/dX, where X(m) is the mole fraction of H2O(m). This approach can reproduce the D(H2O(t)) values to within a factor of 2 in the range of 400-1200°C, 0.1-810 MPa, and 0-7.7% H2O(t). An explicit formula for calculating D(H2O(t)) at H2O(t) ≤ 2% is: where C is H2O(t) content by weight, and C0 equals 1% H2O(t). A formula for calculating D(H2O(t)) at all conditions covered by this work is: where m = -20.79 - 5030/T - 1.4 P/T. The diffusivities obtained in this work can be used to model bubble growth in explosive and nonexplosive rhyolitic volcanic eruptions in all commonly encountered T, P, and H2O(t) conditions. (C) 2000 Elsevier Science B.V. All rights reserved.
Keywords
- Diffusion coefficients, Rhyolitic melt, Speciation, Volatiles, Volcanic eruptions, Water diffusion
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: Chemical geology, Vol. 169, No. 1-2, 15.08.2000, p. 243-262.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - H2O diffusion in rhyolitic melts and glasses
AU - Zhang, Youxue
AU - Behrens, Harald
N1 - Funding Information: We thank O. Navon and A. Proussevitch for careful and insightful reviews. This research is supported by German Christian Kuhlemann Foundation (Germany), German DAAD, and US NSF grant EAR-9972937.
PY - 2000/8/15
Y1 - 2000/8/15
N2 - H2O diffusion plays a major role in bubble growth and volcanic eruption. We report a comprehensive study of H2O diffusion in rhyolitic melts and glasses. This new study and previous investigations together cover a wide range of conditions: 400-1200°C, 0.1-810 MPa, and 0.1-7.7 wt.% total H2O content (H2O). In order to constrain how the diffusivity depends on H2O(t), both the diffusion-couple experiments and the dehydration experiments are carried out in a cold-seal vessel (CSV), an internally heated pressure vessel, and a piston cylinder. H2O concentration profiles are measured by infrared (IR) spectroscopy. Although there are still some experimental and analytical difficulties, our data represent a major improvement over earlier data. The diffusion data have been used to quantify H2O diffusivity as a function of temperature, pressure, and H2O(t). Assuming that molecular H2O (H2O(m)) is the diffusing species, the H2O(m) diffusivity (in μm2/s) can be expressed as: D(H(2)O(m)) = exp[(14.08 - 13,128/T - 2.796 P/T) + (-27.21 + 36,892/T + 57.23 P/T)X], where T is in Kelvin, P is in mPa, and X is the mole fraction of H2O(t) on a single oxygen basis. The pressure dependence is not so well-resolved compared to the dependence on T and X. The dependence of D(H(2)O(m)) on X increases with increasing pressure. The results are consistent with the data of Nowak and Behrens (1997) [Nowak, M., Behrens, H., 1997. An experimental investigation on diffusion of water in haplogranitic melts. Contrib. Mineral. Petrol. 126, 365-376.], but different from the assumption of Zhang et al. (1991a) [Zhang, Y., Stolper, E.M., Wasserburg, G.J., 1991a. Diffusion of water in rhyolitic glasses. Geochim. Cosmochim. Acta 55, 441-456.], because the dependence cannot be resolved from their low-H2O(t) diffusion data, and because the dependence is not so strong at low pressures. The activation energy for H2O(m) diffusion decreases as H2O(t) increases and depends on P (increases with P at X <0.05 and decreases with P at X > 0.05). The results roughly reconcile the different activation energies of Zhang et al. (1991a) and Nowak and Behrens (1997). The total (or bulk) H2O diffusivity (D(H2O(t)) can be calculated from D(H2O(t)) = D(H2O(m)) dX(m)/dX, where X(m) is the mole fraction of H2O(m). This approach can reproduce the D(H2O(t)) values to within a factor of 2 in the range of 400-1200°C, 0.1-810 MPa, and 0-7.7% H2O(t). An explicit formula for calculating D(H2O(t)) at H2O(t) ≤ 2% is: where C is H2O(t) content by weight, and C0 equals 1% H2O(t). A formula for calculating D(H2O(t)) at all conditions covered by this work is: where m = -20.79 - 5030/T - 1.4 P/T. The diffusivities obtained in this work can be used to model bubble growth in explosive and nonexplosive rhyolitic volcanic eruptions in all commonly encountered T, P, and H2O(t) conditions. (C) 2000 Elsevier Science B.V. All rights reserved.
AB - H2O diffusion plays a major role in bubble growth and volcanic eruption. We report a comprehensive study of H2O diffusion in rhyolitic melts and glasses. This new study and previous investigations together cover a wide range of conditions: 400-1200°C, 0.1-810 MPa, and 0.1-7.7 wt.% total H2O content (H2O). In order to constrain how the diffusivity depends on H2O(t), both the diffusion-couple experiments and the dehydration experiments are carried out in a cold-seal vessel (CSV), an internally heated pressure vessel, and a piston cylinder. H2O concentration profiles are measured by infrared (IR) spectroscopy. Although there are still some experimental and analytical difficulties, our data represent a major improvement over earlier data. The diffusion data have been used to quantify H2O diffusivity as a function of temperature, pressure, and H2O(t). Assuming that molecular H2O (H2O(m)) is the diffusing species, the H2O(m) diffusivity (in μm2/s) can be expressed as: D(H(2)O(m)) = exp[(14.08 - 13,128/T - 2.796 P/T) + (-27.21 + 36,892/T + 57.23 P/T)X], where T is in Kelvin, P is in mPa, and X is the mole fraction of H2O(t) on a single oxygen basis. The pressure dependence is not so well-resolved compared to the dependence on T and X. The dependence of D(H(2)O(m)) on X increases with increasing pressure. The results are consistent with the data of Nowak and Behrens (1997) [Nowak, M., Behrens, H., 1997. An experimental investigation on diffusion of water in haplogranitic melts. Contrib. Mineral. Petrol. 126, 365-376.], but different from the assumption of Zhang et al. (1991a) [Zhang, Y., Stolper, E.M., Wasserburg, G.J., 1991a. Diffusion of water in rhyolitic glasses. Geochim. Cosmochim. Acta 55, 441-456.], because the dependence cannot be resolved from their low-H2O(t) diffusion data, and because the dependence is not so strong at low pressures. The activation energy for H2O(m) diffusion decreases as H2O(t) increases and depends on P (increases with P at X <0.05 and decreases with P at X > 0.05). The results roughly reconcile the different activation energies of Zhang et al. (1991a) and Nowak and Behrens (1997). The total (or bulk) H2O diffusivity (D(H2O(t)) can be calculated from D(H2O(t)) = D(H2O(m)) dX(m)/dX, where X(m) is the mole fraction of H2O(m). This approach can reproduce the D(H2O(t)) values to within a factor of 2 in the range of 400-1200°C, 0.1-810 MPa, and 0-7.7% H2O(t). An explicit formula for calculating D(H2O(t)) at H2O(t) ≤ 2% is: where C is H2O(t) content by weight, and C0 equals 1% H2O(t). A formula for calculating D(H2O(t)) at all conditions covered by this work is: where m = -20.79 - 5030/T - 1.4 P/T. The diffusivities obtained in this work can be used to model bubble growth in explosive and nonexplosive rhyolitic volcanic eruptions in all commonly encountered T, P, and H2O(t) conditions. (C) 2000 Elsevier Science B.V. All rights reserved.
KW - Diffusion coefficients
KW - Rhyolitic melt
KW - Speciation
KW - Volatiles
KW - Volcanic eruptions
KW - Water diffusion
UR - http://www.scopus.com/inward/record.url?scp=0033821709&partnerID=8YFLogxK
U2 - 10.1016/S0009-2541(99)00231-4
DO - 10.1016/S0009-2541(99)00231-4
M3 - Article
AN - SCOPUS:0033821709
VL - 169
SP - 243
EP - 262
JO - Chemical geology
JF - Chemical geology
SN - 0009-2541
IS - 1-2
ER -