Details
| Original language | English |
|---|---|
| Pages (from-to) | 275-289 |
| Number of pages | 15 |
| Journal | Chemical Geology |
| Volume | 174 |
| Issue number | 1-3 |
| Publication status | Published - 2001 |
Abstract
The solubility of water in melts of alkali feldspar endmember compositions (MAlSi3O8, M = Li, Na, K, Rb) was investigated at temperatures 825-1420°C and pressures 50-800 MPa. Water contents of isobarically quenched glasses were determined by Karl-Fischer titration (KFT) and/or by near-infrared (NIR) spectroscopy. At given P and T conditions, the mole fraction of dissolved water decreases with increasing alkali radius from Li to K. The water solubility differences between Li-,Na- and K-feldspar compositions are more pronounced at low than at high temperature. For instance, at 500 MPa, the solubility ratio is 1:0.84:0.71 at 900°C and 1:0.87:0.82 at 1200°C. The trend of a decreasing water solubility with increasing alkali radius, however, does not hold for Rb. At 1200°C and 400 and 500 MPa, we found a minimum water solubility for K compared to the other alkali (Li, Na,Rb). This result contrasts with the effect of excess alkali oxide on increasing the water solubility in haplogranitic melts which is according to Dingwell et al. [Dingwell, D.B., Holtz, F., Behrens, H., 1997. The solubility of water in peralkaline and peraluminous granitic melts. Am. Mineral. 82,434-437] on a molar equivalent basis the same for Cs, Rb, K, and Na whereas it is smaller for Li. With increasing pressure, the water solubility the water solubility turns over from a retrograde to a prograde T-dependence at constant pressure. Normalizing the solubility by the fugacity of H2O a negative dependence on temperature is observed in the whole PT range of our experiments indicating regardless of whether OH groups or molecular H2O are the dominating water species in the melt the dissolution enthalpy of water in the melt is positive. The pressure, Pneutral, at which water solubility is independent on T decreases from 700 ± 100 MPa for LiAlSi3O8 (water content ≈ 16.5 wt.%) to 500 ± 50 MPa for Na (water content 11.5 wt.%) to 200 ± 50 MPa for K (water content 5.2 wt.%). For Rb, quench bubbles indicate Pneutral ≪ 300 MPa. P neutral might be related to the critical behavior of the silicate-water system. From the observed trend, we infer that the critical curves of the MAlSi3O8-H2O system in the investigated pressure range progressively shift towards higher T with decreasing ionic radius of the alkali.
Keywords
- Alkali feldspathic Composition, Critical point, Silicate melts, Water solubility
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. 174, No. 1-3, 2001, p. 275-289.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The effect of alkali ionic radius, temperature, and pressure on the solubility of water in MAlSi3O8 melts (M=Li, Na, K, Rb)
AU - Behrens, Harald
AU - Meyer, Michaela C.
AU - Holtz, Francois
AU - Benne, Darja
AU - Nowak, Marcus
N1 - Funding Information: The study has been supported by the European Community (TMR project ERBFMRX-CT96-0063 G). The authors thank C. Romano and D. Dingwell for critically reviewing the paper and giving helpful comments. Copyright: Copyright 2011 Elsevier B.V., All rights reserved.
PY - 2001
Y1 - 2001
N2 - The solubility of water in melts of alkali feldspar endmember compositions (MAlSi3O8, M = Li, Na, K, Rb) was investigated at temperatures 825-1420°C and pressures 50-800 MPa. Water contents of isobarically quenched glasses were determined by Karl-Fischer titration (KFT) and/or by near-infrared (NIR) spectroscopy. At given P and T conditions, the mole fraction of dissolved water decreases with increasing alkali radius from Li to K. The water solubility differences between Li-,Na- and K-feldspar compositions are more pronounced at low than at high temperature. For instance, at 500 MPa, the solubility ratio is 1:0.84:0.71 at 900°C and 1:0.87:0.82 at 1200°C. The trend of a decreasing water solubility with increasing alkali radius, however, does not hold for Rb. At 1200°C and 400 and 500 MPa, we found a minimum water solubility for K compared to the other alkali (Li, Na,Rb). This result contrasts with the effect of excess alkali oxide on increasing the water solubility in haplogranitic melts which is according to Dingwell et al. [Dingwell, D.B., Holtz, F., Behrens, H., 1997. The solubility of water in peralkaline and peraluminous granitic melts. Am. Mineral. 82,434-437] on a molar equivalent basis the same for Cs, Rb, K, and Na whereas it is smaller for Li. With increasing pressure, the water solubility the water solubility turns over from a retrograde to a prograde T-dependence at constant pressure. Normalizing the solubility by the fugacity of H2O a negative dependence on temperature is observed in the whole PT range of our experiments indicating regardless of whether OH groups or molecular H2O are the dominating water species in the melt the dissolution enthalpy of water in the melt is positive. The pressure, Pneutral, at which water solubility is independent on T decreases from 700 ± 100 MPa for LiAlSi3O8 (water content ≈ 16.5 wt.%) to 500 ± 50 MPa for Na (water content 11.5 wt.%) to 200 ± 50 MPa for K (water content 5.2 wt.%). For Rb, quench bubbles indicate Pneutral ≪ 300 MPa. P neutral might be related to the critical behavior of the silicate-water system. From the observed trend, we infer that the critical curves of the MAlSi3O8-H2O system in the investigated pressure range progressively shift towards higher T with decreasing ionic radius of the alkali.
AB - The solubility of water in melts of alkali feldspar endmember compositions (MAlSi3O8, M = Li, Na, K, Rb) was investigated at temperatures 825-1420°C and pressures 50-800 MPa. Water contents of isobarically quenched glasses were determined by Karl-Fischer titration (KFT) and/or by near-infrared (NIR) spectroscopy. At given P and T conditions, the mole fraction of dissolved water decreases with increasing alkali radius from Li to K. The water solubility differences between Li-,Na- and K-feldspar compositions are more pronounced at low than at high temperature. For instance, at 500 MPa, the solubility ratio is 1:0.84:0.71 at 900°C and 1:0.87:0.82 at 1200°C. The trend of a decreasing water solubility with increasing alkali radius, however, does not hold for Rb. At 1200°C and 400 and 500 MPa, we found a minimum water solubility for K compared to the other alkali (Li, Na,Rb). This result contrasts with the effect of excess alkali oxide on increasing the water solubility in haplogranitic melts which is according to Dingwell et al. [Dingwell, D.B., Holtz, F., Behrens, H., 1997. The solubility of water in peralkaline and peraluminous granitic melts. Am. Mineral. 82,434-437] on a molar equivalent basis the same for Cs, Rb, K, and Na whereas it is smaller for Li. With increasing pressure, the water solubility the water solubility turns over from a retrograde to a prograde T-dependence at constant pressure. Normalizing the solubility by the fugacity of H2O a negative dependence on temperature is observed in the whole PT range of our experiments indicating regardless of whether OH groups or molecular H2O are the dominating water species in the melt the dissolution enthalpy of water in the melt is positive. The pressure, Pneutral, at which water solubility is independent on T decreases from 700 ± 100 MPa for LiAlSi3O8 (water content ≈ 16.5 wt.%) to 500 ± 50 MPa for Na (water content 11.5 wt.%) to 200 ± 50 MPa for K (water content 5.2 wt.%). For Rb, quench bubbles indicate Pneutral ≪ 300 MPa. P neutral might be related to the critical behavior of the silicate-water system. From the observed trend, we infer that the critical curves of the MAlSi3O8-H2O system in the investigated pressure range progressively shift towards higher T with decreasing ionic radius of the alkali.
KW - Alkali feldspathic Composition
KW - Critical point
KW - Silicate melts
KW - Water solubility
UR - http://www.scopus.com/inward/record.url?scp=0035088965&partnerID=8YFLogxK
U2 - 10.1016/S0009-2541(00)00320-X
DO - 10.1016/S0009-2541(00)00320-X
M3 - Article
AN - SCOPUS:0035088965
VL - 174
SP - 275
EP - 289
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
IS - 1-3
ER -