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2015
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.

2014
Pichavant, M, Scaillet B, Pommier A, Iacono-Marziano G, Cioni R.  2014.  Nature and evolution of primitive Vesuvius magmas: An experimental study. Journal of Petrology. 55:2281-2309.   10.1093/petrology/egu057   AbstractWebsite

Two mafic eruptive products from Vesuvius, a tephrite and a trachybasalt, have been crystallized in the laboratory to constrain the nature of primitive Vesuvius magmas and their crustal evolution. Experiments were performed at high temperatures (from 1000 to a parts per thousand yen1200A degrees C) and both at 0 center dot 1 MPa and at high pressures (from 50 to 200 MPa) under H2O-bearing fluid-absent and H2O- and CO2-bearing fluid-present conditions. Experiments started from glass except for a few that started from glass plus San Carlos olivine crystals to force olivine saturation. Melt H2O concentrations reached a maximum of 6 center dot 0 wt % and experimental fO(2) ranged from NNO - 0 center dot 1 to NNO + 3 center dot 4 (where NNO is nickel-nickel oxide buffer). Clinopyroxene (Mg# up to 93) is the liquidus phase for the two investigated samples; it is followed by leucite for H2O in melt < 3 wt %, and by phlogopite (Mg# up to 81) for H2O in melt > 3 wt %. Olivine (Fo(85)) crystallized spontaneously in only one experimental charge. Plagioclase was not found. Upon progressive crystallization of clinopyroxene, glass K2O and Al2O3 contents strongly increase whereas MgO, CaO and CaO/Al2O3 decrease; the residual melts follow the evolution of Vesuvius whole-rocks from trachybasalt to tephrite, phonotephrite and to tephriphonolite. Concentrations of H2O and CO2 in near-liquidus 200 MPa glasses and primitive melt inclusions from the literature overlap. The earliest evolutionary stage, corresponding to the crystallization of Fo-rich olivine, was reconstructed by the olivine-added experiments. They show that the primitive Vesuvius melts are trachybasalts (K2O similar to 4 center dot 5-5 center dot 5 wt %, MgO = 8-9 wt %, Mg# = 75-80, CaO/Al2O3 = 0 center dot 9-0 center dot 95) that crystallize Fo-rich olivine (90-91) as the liquidus phase between 1150 and 1200A degrees C and from 300 to < 200 MPa. Primitive Vesuvius melts are volatile-rich (1 center dot 5-4 center dot 5 wt % H2O and 600-4500 ppm CO2 in primitive melt inclusions) and oxidized (from NNO + 0 center dot 4 to NNO + 1 center dot 2). Assimilation of carbonate wall-rocks by ascending primitive magmas can account for the disappearance of olivine from crystallization sequences and explains the lack of rocks representative of olivine-crystallizing magmas. A correlation between carbonate assimilation and the type of feeding system is proposed: carbonate assimilation is promoted for primitive magma batches of small volumes. In contrast, for longer-lived, large-volume, less frequently recharged, hence more evolved, cooler reservoirs, magma-carbonate interaction is limited. Primitive magmas from Vesuvius and other Campanian volcanoes have similar redox states. However, the Cr# of Vesuvius spinels is distinctive and therefore the peridotitic component in the mantle source of Vesuvius differs from that of the other Campanian magmas.