| Autor: |
Allabar, Anja, Petri, Patricia L., Eul, Dennis, Nowak, Marcus |
| Předmět: |
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| Zdroj: |
Contributions to Mineralogy & Petrology; May2022, Vol. 177 Issue 5, p1-17, 17p |
| Abstrakt: |
The H2O solubility in peralkaline haplogranitic melts has been experimentally determined as a function of pressure (27–200 MPa) and temperature (1123–1523 K). The compositions were based on Ab38Or34Qz28 (AOQ) with 4 and 8 wt% Na2O in excess. H2O solubility experiments were performed in an internally heated pressure vessel and quenched to glasses for analysis. For quantification of H2O contents in the glasses using FTIR analysis, the linear molar absorption coefficients as a function of Na2O excess with respect to AOQ composition were determined, as well as the glass densities as a function of H2O concentration. The H2O solubility increases with increasing pressure, decreasing temperature, and with increasing peralkalinity. A linear dependence between Na2O excess (wt%) and H2O solubility (wt%) was found. It has been previously shown that on a molar basis the different alkalis contribute similarly to the H2O solubility increase so that H2O solubility increases linearly with excess alkali (difference between mole fractions of alkalis and that of alumina). Thus, the dependence of H2O solubility on pressure, temperature and excess alkali obtained from the new data of this study allow a simple prediction of H2O solubility for peralkaline rhyolitic melts based on the excess alkali content. This new empirical model was tested with H2O solubility data from literature for peralkaline haplogranitic and natural peralkaline rhyolitic melt compositions, yielding good agreement (< 10% deviation) between predicted and observed H2O solubility, which is an improvement compared to previous models. The model can be applied to natural peralkaline rhyolitic melts that occur, e.g. on Pantelleria, Gran Canaria, or the East African Rift. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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