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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.

Caricchi, L, Pommier A, Pistone M, Castro J, Burgisser A, Perugini D.  2011.  Strain-induced magma degassing: insights from simple-shear experiments on bubble bearing melts. Bulletin of Volcanology. 73:1245-1257.   10.1007/S00445-011-0471-2   AbstractWebsite

Experiments have been performed to determine the effect of deformation on degassing of bubble-bearing melts. Cylindrical specimens of phonolitic composition, initial water content of 1.5 wt.% and 2 vol.% bubbles, have been deformed in simple-shear (torsional configuration) in an internally heated Paterson-type pressure vessel at temperatures of 798-848 K, 100-180 MPa confining pressure and different final strains. Micro-structural analyses of the samples before and after deformation have been performed in two and three dimensions using optical microscopy, a nanotomography machine and synchrotron tomography. The water content of the glasses before and after deformation has been measured using Fourier Transform Infrared Spectroscopy (FTIR). In samples strained up to a total of gamma similar to 2 the bubbles record accurately the total strain, whereas at higher strains (gamma similar to 10) the bubbles become very flattened and elongate in the direction of shear. The residual water content of the glasses remains constant up to a strain of gamma similar to 2 and then decreases to about 0.2 wt.% at gamma similar to 10. Results show that strain enhances bubble coalescence and degassing even at low bubble volume-fractions. Noticeably, deformation produced a strongly water under-saturated melt. This suggests that degassing may occur at great depths in the volcanic conduit and may force the magma to become super-cooled early during ascent to the Earth's surface potentially contributing to the genesis of obsidian.