HR: 0830h
AN: T11C-0408    [PDF]
TI: The Viscosity of Peridotite Liquid up to 6.9 GPa Measured by in-situ Falling Sphere Viscometry
AU: Schmickler, B
EM: bettina.schmickler@uni-bayreuth.de
AF: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, 95440 Germany
AU: * Liebske, C
EM: christian.liebske@uni-bayreuth.de
AF: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, 95440 Germany
AU: Terasaki, H
EM: hidenori.terasaki@uni-bayreuth.de
AF: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, 95440 Germany
AU: Suzuki, A
EM: a-suzuki@mail.cc.tohoku.ac.jp
AF: Tohoku University, Institut of Mineralogy, Petrology and Economic Geology, Sendai, 980-8578 Japan
AU: Poe, B T
EM: poe@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, Rom, 00143 Italy
AU: Funakoshi, K
EM: funakosi@spring8.or.jp
AF: Japan Synchrotron Radiation Institute, Mikazuki-cho, Sayo-gun, Hyogo, 679-5198 Japan
AU: Ando, R
AF: Tohoku University, Institut of Mineralogy, Petrology and Economic Geology, Sendai, 980-8578 Japan
AU: Rubie, D C
EM: david.rubie@uni-bayreuth.de
AF: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, 95440 Germany
AB: The viscosity of silicate melts plays an important role in controlling magmatic processes in the Earth. In particular, the viscosity of molten peridotite at mantle pressures is a crucial parameter for modeling the dynamics and crystallization of a deep magma ocean and early differentiation processes within the Earth. The viscosity of peridotite liquid has been measured between 2.5 and 6.9 GPa and temperatures between 2043 K and 2323 K. by in-situ falling sphere viscometry involving a x-ray- radiographic method with a high resolution CCD camera. Experiments were conducted in a multianvil apparatus at SPring-8 synchrotron facility in Japan. In order to avoid the sphere dropping while heating through the broad sub-liquidus region (around 400 K) we have developed a new capsule design which delays the drop of the sphere until stable temperature conditions above the liquidus are reached. This is achieved by initially locating the rhenium sphere outside the hotspot of the furnace at the end of a stepped molybdenum capsule. In addition, the sphere is embedded in a mixture of forsterite (Fo) and Enstatite (En) with the same Si/Mg ratio as the peridotite composition but with a higher melting temperature. Restricting the volume of the Fo-En mixture to 6% of the total sample minimizes its effect in contaminating the peridotite liquid. Experiments were performed between 2.5 and 6.9 GPa. Measured viscosities range from 0.13 Pa$\cdot$ s at 2093 K and 2.5 GPa to 0.02 Pa$\cdot$ s at 2223 K and 3.4 GPa. An Arrhenius equation was fitted to the data, giving an activation energy of 256 $\pm$ 44 kJ/mol. The viscosity increases with pressure, giving a positive activation volume of 6.0 $\pm$ 2 $\rm cm^3/mol$ in the investigated pressure range. Using these parameters to extrapolate our experimental data indicates that the viscosity of a magma ocean will increase by three orders of magnitude at constant temperature when the pressure increases to 30 GPa (depth of about 800 km). A decrease in viscosity of about 1.2 log units is expected if the temperature increases from 2573 to 3273 K. Our results are compared with recent viscosity data for diopside liquid which has been considered as a simple analog for a peridotitic composition.
DE: 1749 Volcanology, geochemistry, and petrology
DE: 8439 Physics and chemistry of magma bodies
SC: Tectonophysics [T]
MN: 2003 Fall Meeting