Multicomponent diffusion in the molten system K2O-Na2O-Al2O3-SiO2-H2O

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doi: 10.2138/am-1998-7-802
Authors:Mungall, James E.; Romano, Claudia; Dingwell, Donald B.
Author Affiliations:Primary:
Universität Bayreuth, Bayerisches Geoinstitut, Bayreuth, Federal Republic of Germany
Other:
Ixion Research, Canada
Universita di Roma Tre, Italy
Volume Title:American Mineralogist
Source:American Mineralogist, 83(7-8), p.685-699. Publisher: Mineralogical Society of America, Washington, DC, United States. ISSN: 0003-004X
Publication Date:1998
Note:In English. 44 refs.; illus., incl. 4 tables
Summary:We have measured multicomponent chemical diffusion coefficients in a melt near to the low pressure water-saturated eutectic granite composition in the system K2O-Na2O-Al2O3-SiO2-H2O at 1.0 GPa and temperatures of 1300 and 1600°C. The measured diffusion profiles can be accounted for within the analytical error by diffusion coefficients, which are not dependent on composition within the range of compositions accessed by our experiments. The multicomponent diffusion coefficient matrix [D] has a highly degenerate set of real, positive eigenvalues that show a regular relation to melt viscosity on an Arrhenius diagram. The smallest eigenvalue is that associated predominantly with Si-Al exchange. The larger two eigenvalues are those associated predominantly with Si-Al exchange. The larger two eigenvalues are those associated with Si-Na and Si-K exchange and are effectively degenerate, with the result that exchanges of alkalis for silica or for each other can proceed in pseudo-binary fashion without inducing fluxes of other components. The eigenvalue associated with H-Si exchange is smaller than the alkali-silica eigenvalues, but analytical uncertainties make it also effectively degenerate with the alkalis. Uphill diffusion, notably of water and alkalis, was observed in several experiments, and this would lead to transient partitioning of water and alkalis across diffusion interfaces showing large Al2O3 concentration gradients. Such partitioning in natural systems would persist until Al concentration gradients were erased by continued, much slower Al-Si interdiffusion.
Sections:Experimental mineralogy
Subsections:General
Subjects:Alkali granites; Diffusion; Eigenvalues; Geochemistry; Granites; High pressure; High temperature; Igneous rocks; Magmas; Melts; Phase transitions; Plutonic rocks; Pressure; Quantitative analysis; Temperature; Thermodynamic properties
Abstract Numbers:99M/1479
Record ID:1998054258
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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