HR: 13:40h
AN: T42D-01    [PDF]
TI: Viscosity of a molten mantle: experimental data for liquid peridotite.
AU: * Dingwell, D B
EM: Dingwell@lmu.de
AF: University of Munich, Theresienstr. 41, Munich, 80333 Germany
AU: Courtial, P
AF: University of Munich, Theresienstr. 41, Munich, 80333 Germany
AU: Giordano, D
AF: University of Munich, Theresienstr. 41, Munich, 80333 Germany
AU: Nichols, A
AF: University of Munich, Theresienstr. 41, Munich, 80333 Germany
AB: The debate surrounding Earth evolution accompanied by a largely molten magma is increasingly reliant on the results of models for physico-chemical processes in such a scenario. To date, the primary emphasis in the physical characterisation of molten peridotite has been the determination of a PVT equation of state with contributions from shock-wave and buoyancy studies. Determinations or other melt properties are largely lacking. The viscosity, in particular, has received too little attention. Here, the Newtonian viscosity of molten peridotite has been determined experimentally at superliquidus and supercooled conditions. The high temperature determinations were obtained using a concentric cylinder technique employing constant high-speed deformation. The low temperature determinations have been obtained from the analysis of the glass transition in scanning calorimetric traces and conversion via published shift factors into viscosity data. These latter measurements were made possible by the experimental synthesis of peridotite glass using a splat-quenching device. Taken together the superliquidus and supercooled data provide the first quantitative description of the viscosity of molten peridotite. The temperature-dependence of the viscosity of molten peridotite is extremely non-Arrhenian. As a result, molten peridotite, despite having an extremely low viscosity near its liquidus temperature, exhibits a very high glass transition temperature. The extrapolation of viscosity in terms of temperature is of central importance to the application of these data to nature. The viscosity data presented here cover over 12 log units of viscosity and 800K. As a result, this data set provides a robust basis for the extrapolation of melt viscosity to the even higher temperatures expected to exist where molten peridotite is or was present in the mantle. Further influences on the viscosity of peridotite, such as volatiles and pressure, are expected to play a relatively minor role. Extrapolated values of these peridotite viscosity data are compared with those estimated for nonsilicate liquids at pressure-temperature conditions for a molten mantle in the Earth.
DE: 8439 Physics and chemistry of magma bodies
SC: Tectonophysics [T]
MN: 2003 Fall Meeting