HR: 0800h
AN: V41A-1351    [Abstracts]
TI: A partial molar volume for ZnO in silicate melts.
AU: Ledda, B
AF: Scienze della Terra, Universit  di Camerino, Camerino, 62032 Italy
AU: * Potuzak, M
AF: Earth and Environment, University of Munich, Theresienstr. 41/III, Munich, 80333 Germany
AU: Dingwell, D B
EM: Dingwell@lmu.de
AF: Earth and Environment, University of Munich, Theresienstr. 41/III, Munich, 80333 Germany
AU: Courtial, P
AF: Earth and Environment, University of Munich, Theresienstr. 41/III, Munich, 80333 Germany
AB: Trace elements in igneous petrology have, in comparison with major elements, a relevance in the petrogenetic modelling of magmatic differentiation that far outweighs their relative abundance. Optimal use of the information contained in trace element variations within igneous phases requires an accurate description of their partitioning behaviour as a function of phase composition and structure, as well as temperature and pressure. In this manner, the partial molar thermodynamic properties of trace elements in silicate melts may contribute to the petrogenetic modelling of such systems. With this in mind, a series of investigations into the partial molar properties of trace elements in silicate melts have been carried out in recent years. Here we extend this work to the analysis of the volumetric properties of ZnO in silicate melts. Densities of 8 Zn-bearing silicate melts have been determined in air in the temperature range of 1363 to 1850 K. The compositional joins investigated (sodium disilicate (NS2) - ZnO; anorthite-diopside 1 bar eutectic (AnDi) - ZnO; and diopside - petedunnite) were chosen based on the pre-existing experimental density data set, their petrological relevance and to provide a test for significant compositionally induced variations in the structural role of ZnO. The ZnO concentrations investigated range up to 25 mol% for sodium disilicate, 20 mol% for the anorthite-diopside 1 atm eutectic and 100 mol% petedunnite. Molar volumes and expansivities of all melts have been derived. The molar volumes of the present liquids all decrease with increasing ZnO content. The partial molar volume of ZnO derived here from the volumetric measurements for each binary system is the same within error. A multicomponent fit to the volumetric data for all compositions yields a value of 14.141(0.730) cm$^{3}$.mol$^{-1}$ at 1300 K. We find, herewith, no volumetric evidence for compositionally-induced coordination number variations for ZnO in alkali-bearing versus alkali-free silicate melts.
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting