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2010
Pommier, A, Tarits P, Hautot S, Pichavant M, Scaillet B, Gaillard F.  2010.  A new petrological and geophysical investigation of the present-day plumbing system of Mount Vesuvius. Geochemistry Geophysics Geosystems. 11   10.1029/2010gc003059   AbstractWebsite

A model of the electrical resistivity of Mt. Vesuvius has been elaborated to investigate the present structure of the volcanic edifice. The model is based on electrical conductivity measurements in the laboratory, on geophysical information, in particular, magnetotelluric (MT) data, and on petrological and geochemical constraints. Both 1-D and 3-D simulations explored the effect of depth, volume and resistivity of either one or two reservoirs in the structure. For each configuration tested, modeled MT transfer functions were compared to field transfer functions from field magnetotelluric studies. The field electrical data are reproduced with a shallow and very conductive layer (similar to 0.5 km depth, 1.2 km thick, 5 ohm. m resistive) that most likely corresponds to a saline brine present beneath the volcano. Our results are also compatible with the presence of cooling magma batches at shallow depths (<3-4 km depth). The presence of a deeper body at similar to 8 km depth, as suggested by seismic studies, is consistent with the observed field transfer functions if such a body has an electrical resistivity > similar to 100 ohm. m. According to a petro-physical conductivity model, such a resistivity value is in agreement either with a low-temperature, crystal-rich magma chamber or with a small quantity of hotter magma interconnected in the resistive surrounding carbonates. However, the low quality of MT field data at long periods prevent from placing strong constraints on a potential deep magma reservoir. A comparison with seismic velocity values tends to support the second hypothesis. Our findings would be consistent with a deep structure (8-10 km depth) made of a tephriphonolitic magma at 1000 degrees C, containing 3.5 wt%H2O, 30 vol.% crystals, and interconnected in carbonates in proportions similar to 45% melt -55% carbonates.

2008
Pommier, A, Gaillard F, Pichavant M, Scaillet B.  2008.  Laboratory measurements of electrical conductivities of hydrous and dry Mount Vesuvius melts under pressure. Journal of Geophysical Research-Solid Earth. 113   10.1029/2007jb005269   AbstractWebsite

[1] Quantitative interpretation of MT anomalies in volcanic regions requires laboratory measurements of electrical conductivities of natural magma compositions. The electrical conductivities of three lava compositions from Mount Vesuvius (Italy) have been measured using an impedance spectrometer. Experiments were conducted on both glasses and melts between 400 and 1300 degrees C, at both ambient pressure in air and high pressures (up to 400 MPa). Both dry and hydrous (up to 5.6 wt % H2O) melt compositions were investigated. A change of the conduction mechanism corresponding to the glass transition was systematically observed. The conductivity data were fitted by sample-specific Arrhenius laws on either side of Tg. The electrical conductivity increases with temperature and is higher in the order tephrite, phonotephrite to phonolite. For the three investigated compositions, increasing pressure decreases the conductivity, although the effect of pressure is relatively small. The three investigated compositions have similar activation volumes (Delta V= 16-24 cm(3) mol(-1)). Increasing the water content of the melt increases the conductivity. Comparison of activation energies (Ea) from conductivity and sodium diffusion and use of the Nernst-Einstein relation allow sodium to be identified as the main charge carrier in our melts and presumably also in the corresponding glasses. Our data and those of previous studies highlight the correlation between the Arrhenius parameters Ea and sigma(0). A semiempirical method allowing the determination of the electrical conductivity of natural magmatic liquids is proposed, in which the activation energy is modeled on the basis of the Anderson-Stuart model, sigma(0) being obtained from the compensation law and Delta V being fitted from our experimental data. The model enables the electrical conductivity to be calculated for the entire range of melt compositions at Mount Vesuvius and also satisfactorily predicts the electrical response of other melt compositions. Electrical conductivity data for Mount Vesuvius melts and magmas are slightly lower than the electrical anomaly revealed by MT studies.