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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.

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.