HR: 1340h
AN: MR13A-0074    [Abstracts]
TI: The Albite Fusion Curve Re-examined: New Experiments and the Density and Compressibility of NaAlSi₃O₈ Liquid With Pressure
AU: * Tenner, T J
EM: tenn0047@umn.edu
AF: University of Michigan, Department of Geoligical Sciences 1100 N. University Ave., Ann Arbor, MI 48109 United States
AU: Lange, R A
EM: becky@umich.edu
AF: University of Michigan, Department of Geoligical Sciences 1100 N. University Ave., Ann Arbor, MI 48109 United States
AB: Two half-reversals on the melting temperature of high albite (NaAlSi₃O₈) were determined at 2.3 GPa (1360-1370 °C) and 2.8 GPa (1383-1389 °C) in a piston-cylinder apparatus with NaAlSi₃O₈ glass as the starting material. A detailed thermal gradient across the sample capsule was mapped, which showed a 3.5 °C gradient across the upper third of the sample capsule and a 30 °C gradient across the lower two-thirds. A calibration against the melting curve of NaCl showed a -5 % pressure correction for the BaCO3/MgO/graphite pressure medium used in these experiments. In addition to the glass-crystal half-reversals, a crystal-glass half-reversal at 2.73 GPa was obtained (1389-1399 °C) using high albite as the starting material. All run products that quenched to a glass were analyzed by Fourier-transform infrared spectroscopy and were found to contain < 0.045 wt% H₂O. Our experimental constraints on the albite fusion curve are in excellent agreement with those of Birch and LeComte (1960) and Boyd and England (1963), but deviate from those of Boettcher et al. (1982). Our new data on the albite fusion curve at high pressure are compared with the calculated melting reaction based on the best available thermodynamic data at one bar (Lange, 2003), and various values for the pressure dependence of liquid compressibility (K' = dK_T,0/dP, where K_T,0 = 1/β_T,0) for NaAlSi₃O₈ liquid, using the 3rd-order Birch-Murnaghan equation of state. Our phase-equilibrium data match the fusion curve calculated with a liquid value of 10.0 ± 1.0. This allows the density of NaAlSi₃O₈ liquid to be calculated at 1500 °C and 3.0 GPa (2.551 ± 0.01 g/cm₃), with an uncertainty that is ~0.3 %. The results of this study show that the density and compressibility of this viscous and fully polymerized liquid can be calculated to high pressure (~3 GPa) with a remarkably high precision. Owing to the absence of any coordination change in NaAlSi₃O₈ liquid to ~8 GPa, calculations of its density and compressibility can likely be extended to this pressure.
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005