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Melt Energetics at High Temperature and Pressure

Published online by Cambridge University Press:  10 February 2011

Martin C. Wilding  and
Alexandra Navrotsky
Martin C. Wilding
Affiliation:
Thermochemistry Facility, University of California at Davis, Davis, CA 95616–8779, mcwilding@ucdavis.edu
Alexandra Navrotsky
Affiliation:
Thermochemistry Facility, University of California at Davis, Davis, CA 95616–8779, mcwilding@ucdavis.edu
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Abstract

The physical behavior of silicate liquids at high pressure is important in modeling the dynamic processes of the deep earth. The density of the silicate liquids determines the transport properties of silicate melts and volumetric properties of silicate melts are therefore of prime importance. However, the partial molar volumes of melt components are difficult to evaluate since it is difficult to observe the molten state at high pressure. A variety of approaches are used to investigate silicate melt properties. Individual melt components can be used and complex mixing terms used to describe mixing behavior. Alternatively the melt species themselves can be investigated, although there is little information as to what these actually are. In both cases the accurate determination of the dP/dT slope of the melting curves is critical.

Speciation reactions can be studied in situ at one atmosphere through high temperature calorimetry. An approach has been developed where the dissolution of melt components which are readily soluble in silicate solvents and which have a large heat effect can be used to determine the dependence of the activities of these components on melt structure. In addition the high temperature calorimetrie data can be used in combination with solution calorimetrie data at lower temperatures to evaluate the temperature-dependent stability of these melt species. These studies are independent of and complementary to spectroscopie determinations and provide a description of the temperature-dependence of melt structure at one atmosphere. Recent studies have focused on the solution of La2O3 and TiO2 in model silicate melts to assess the role of melt structure in the complexing of these components. The next obvious step is to extrapolate to high pressure. One possible approach is to combine one atmosphere data with existing melting relationships to determine the optimized melt compositions for a model natural systems. The next step is to then assess the stability of melt species from the partial molar properties and the partitioning of the elements between coexisting melts and mineral phases at pressures and temperatures of interest.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 499: Symposium DD – High Pressure Materials Research , 1997 , 185
Copyright
Copyright © Materials Research Society 1998

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References

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