HR: 1340h
AN: MR13B-1262    [Abstracts]
TI: Thermal diffusivity of pyroxene, feldspar, and silica melts, glasses, and single-crystals at high temperature
AU: * Pertermann, M
EM: maik.pertermann@rice.edu
AF: Dept. Earth Sci., Rice University, Houston, TX 77005, United States
AU: Branlund, J
EM: joyb@wustl.edu
AF: Dept. EPSc, Washington U., St. Louis, MO 63130, United States
AU: Whittington, A
EM: whittingtona@missouri.edu
AF: Dept. Geological Sci., University of Missouri, Columbia, MO 65211, United States
AU: Hofmeister, A
EM: hofmeist@wustl.edu
AF: Dept. EPSc, Washington U., St. Louis, MO 63130, United States
AB: Thermal diffusivity (D) due to phonon transport (the lattice component) was measured using laser-flash analysis from oriented single-crystals and of glasses above the glass transition, which proxy as melts. Compositions include SiO₂, CaMgSi₂O₆, LiAlSi₂O₆, NaAlSi₃O₈, and CaAl₂Si₂O₈. KAlSi₃O₈ was studied previously. Viscosity measurements of the supercooled liquids, in the range 10^6.8 to 10^12.3 Pas, confirm near-Arrhenian behavior. For all compositions and for crystal and glass, D decreases with T, approaching a constant generally near 1000 K: D_sat, which is larger in the crystal than in the glass. A rapid decrease in D as T is increased further (ca 1400 K for orthoclase) is consistent with crossing the glass transition, verified from our viscosity data on these systems. The amount of the decrease depends on the chemical composition and similar to the relative decrease observed in heat capacity. Orthoclase values for D_sat are 0.65± 0.3 mm²/s for bulk crystal and 0.53+/-0.03 mm²/s for the glass. Constant D = 0.475+/-.01 mm²/s represents melt. Thermal conductivity (k_lat) of orthoclase glass, calculated using previous results for heat capacity (C_P) and our density data, increases with T due to C_P strongly increasing with T, reaching a plateau near 1.45 W/m-K for melt, but is always below k_lat of the crystal. Similar results were obtained from the other systems studied. Melting of silica, pyroxene, and feldspars impedes heat transport, providing positive thermal feedback that may promote further melting in the continental crust. The consistency of the behavior for these different compositions and structures suggests that our results are universal, holding for oceanic lithosphere as well. Melts, due to being disordered, are poor transporters of heat via vibrations. However, d(ln k_lat)/dP depends inversely on bulk modulus, suggesting that at some high pressure, the thermal conductivity of the melt and corresponding crystal become equal so that retention of heat by melts may not occur deep inside the Earth.
DE: 3619 Magma genesis and partial melting (1037)
DE: 3924 High-pressure behavior
DE: 5139 Transport properties
DE: 8130 Heat generation and transport
DE: 8145 Physics of magma and magma bodies
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting