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Pommier, A, Leinenweber K, Tasaka M.  2015.  Experimental investigation of the electrical behavior of olivine during partial melting under pressure and application to the lunar mantle. Earth and Planetary Science Letters. 425:242-255.   10.1016/j.epsl.2015.05.052   AbstractWebsite

Electrical conductivity measurements were performed during melting experiments of olivine compacts (dry and hydrous Fo(77) and Fo(90)) at 4 and 6 GPa in order to investigate melt transport properties and quantify the effect of partial melting on electrical properties. Experiments were performed in the multi-anvil apparatus and electrical measurements were conducted using the impedance spectroscopy technique with the two-electrode method. Changes in impedance spectra were used to identify the transition from an electrical response controlled by the solid matrix to an electrical response controlled by the melt phase. This transition occurs slightly above the solidus temperature and lasts until T-solidus + 75 degrees C (+/- 25). At higher temperature, a significant increase in conductivity (corresponding to an increase in conductivity values by a factor ranging from similar to 30 to 100) is observed, consistent with the transition from a tube-dominated network to a structure in which melt films and pools become prominent features. This increase in conductivity corresponds to an abrupt jump for all dry samples and to a smoother increase for the hydrous sample. It is followed by a plateau at higher temperature, suggesting that the electrical response of the investigated samples lacks sensitivity to temperature at an advanced stage of partial melting. Electron microprobe analyses on quenched products indicated an increase in Mg# (molar Mg/(Mg + Fe)) of olivine during experiments (similar to 77-93 in the quenched samples with an initial Fo(77) composition and similar to 92-97 in the quenched samples with an initial Fo(90) composition) due to the partitioning of iron to the melt phase. Assuming a respective melt fraction of 0.10 and 0.20 before and after the phase of significant increase in conductivity, in agreement with previous electrical and permeability studies, our results can be reproduced satisfactorily by two-phase electrical models (the Hashin and Shtrikman bounds and the modified brick layer model), and provide a melt conductivity value of 78 (+/- 8) S/m for all Fo(77) samples and 45 (+/- 5) S/m for the Fo(90) sample. Comparison of our results with electromagnetic sounding data of the deep interior of the Moon supports the hypothesis of the presence of interconnected melt at the base of the lunar mantle. Our results underline that electrical conductivity can be used to investigate in situ melt nucleation and migration in the interior of terrestrial planets. (C) 2015 Elsevier B.V. All rights reserved.

Pommier, A, Le-Trong E.  2011.  "SIGMELTS": A web portal for electrical conductivity calculations in geosciences. Computers & Geosciences. 37:1450-1459.   10.1016/J.Cageo.2011.01.002   AbstractWebsite

Electrical conductivity measurements in the laboratory are critical for interpreting geoelectric and magnetotelluric profiles of the Earth's crust and mantle. In order to facilitate access to the current database on electrical conductivity of geomaterials, we have developed a freely available web application (SIGMELTS) dedicated to the calculation of electrical properties. Based on a compilation of previous studies, SIGMELTS computes the electrical conductivity of silicate melts, carbonatites, minerals, fluids, and mantle materials as a function of different parameters, such as composition, temperature, pressure, water content, and oxygen fugacity. Calculations on two-phase mixtures are also implemented using existing mixing models for different geometries. An illustration of the use of SIGMELTS is provided, in which calculations are applied to the subduction zone-related volcanic zone in the Central Andes. Along with petrological considerations, field and laboratory electrical data allow discrimination between the different hypotheses regarding the formation and rise from depth of melts and fluids and quantification of their storage conditions. (C) 2011 Elsevier Ltd. All rights reserved.