HR: 1340h
AN: MR13A-0063    [Abstracts]
TI: Sound Speed and Compressibility Measurements for CaO-MgO-Al2O3-SiO2 Liquids
AU: * Ai, Y
EM: yuhui@umich.edu
AF: Department of geological sciences, University of Michigan, Ann Arbor, 2534 C.C.Little Building 1100 N. University , Ann Arbor, MI 48109-1005 United States
AU: Lange, R A
EM: becky@umich.edu
AF: Department of geological sciences, University of Michigan, Ann Arbor, 2534 C.C.Little Building 1100 N. University , Ann Arbor, MI 48109-1005 United States
AB: Sound speeds in 11 liquids in the CaO-MgO-Al2O3-SiO2 system were measured with a frequency sweep acoustic interferometer between 1410 and 1620°C at one bar. Frequencies varied from 4MHz to 7 MHz, which permitted a test of whether the sound speed data were fully relaxed. In all cases, the sound speeds in the liquids either remain constant or decrease with increasing temperature. The adiabatic and isothermal compressibility of each liquid was deduced accordingly, given the density of each of the liquid measured by Lange and Carmichael (1987). Relaxed sound speed data for three CaO-MgO-SiO2 and three MgO-Al2O3-SiO2 liquids were combined to fit a regression model in which the partial molar sound speed of each oxide component adds linearly. The results led to the following fitted partial molar sound speeds (ñ one sigma) at 1673 K: SiO2 = 2345 ñ 26 m/s, Al2O3 = 3547 ñ 67 m/s, MgO = 3061 ñ 24 m/s and CaO = 4390 ñ 24 m/s. The only component that has a thermal dependence to its sound speed is CaO: -0.72 ñ 0.10 m/s per K. The model recovers all measurements with a standard error of 10 m/s and an average deviation of 0.24 %. The fitted partial molar sound speed for the Al2O3 component in MgO-SiO2 liquids (~3550 m/s) is distinctly different from that found in Na2O-SiO2 liquids (~4500 m/s; Kress et al., 1988) and CaO-SiO2 liquids (~2250 m/s; Rivers and Carmichael, 1987; Webb and Courtial, 1996; this study) for liquids with ≥ 25 mol % SiO2. Our sound speed measurements on three CaO-MgO-Al2O3-SiO2 liquids indicate an average partial molar sound speed for Alª2O3 of ~2563 ñ 286 m/s, which is broadly intermediate between that in MgO-Al2O3-SiO2 and CaO-Al2O3-SiO2 liquids. For all the liquids considered, the partial molar volume of Al2O3 (and all other oxide components) was shown to be independent of both composition and temperature at one bar (Lange and Carmichael, 1987; Lange, 1997). However, the results of the sound speed measurements require that the sound speed and thus compressibility of the Al2O3 component changes with melt composition and is most compressible in CaO-Al2O3-SiO2 liquids and least compressible in Na2O-Al2O3-SiO2 liquids. This in turn indicates that the partial molar volume of the Al2O3 component is no longer independent of composition at elevated pressure. Thus the partial molar volumes of the oxide components in aluminosilicate liquids do not mix ideally at mantle pressures.
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3630 Experimental mineralogy and petrology
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005