Priscille Lesne

Experimental parametrization of magma mixing : application to the 1530 AD eruption of La Soufrière, Guadeloupe (Lesser Antilles)

New petrological data on eruption products and experimental results are integrated and a model for the evolution of the La Soufriere (Guadeloupe, Lesser Antilles arc) magma reservoir prior to the 1530 AD eruption is presented. In comparison with recent volcanic crises in the Antilles, the 1530 AD eruption is distinctive. The eruptive pyroclastic sequence shows a continuous zonation in whole-rock composition from silicic (∼ 62 wt% SiO2) to mafic andesite (∼ 55 wt% SiO2). Mafic products are estimated to be 80% of the total eruption volume. All juvenile clasts are crystal-rich (46-60 vol.% phenocrysts), the crystallinity being inversely correlated with the bulk-rock SiO2 content. The phenocryst assemblage (plagioclase, orthopyroxene, clinopyroxene, magnetite) is constant throughout the sequence. Complexly zoned crystals are encountered, but An60-65, En56-59 and Mt66-68 compositions occur in all samples. Glass inclusions are rhyolitic with up to 5-5.5 wt % H2O. Matrix glasses are strongly heterogeneous, from ∼64 to > 76 wt % SiO2. The pre-eruptive evolution of the reservoir is dominated by the remobilization of a resident andesitic body following the arrival of a basaltic magma batch. Conditions of early remobilization are constrained from experiments on a basalt from the L’Echelle scoria cone. The arrival magma is a crystal-poor, moderately hot (975-1025 °C), wet (> 5 wt % H2O) and oxidized (NNO+1) low-MgO high alumina basalt similar to those involved in other Antilles volcanic centers. Geothermometry and experiments on a silicic andesite product of the eruption show that, for melt H2O contents between 5 and 5.5 wt %, phenocrysts and interstitial melt in the resident magma were in mutual equilibrium at ∼875 °C and NNO+0.8. However, matrix glass and glass inclusion compositions show that, locally, the andesite body was as cold as 825 °C. Melt volatile concentrations imply a minimum depth for the magma reservoir between 5.6 and 7.1 km, and the absence of amphibole phenocrysts indicates a maximum depth at 8.5 km. The 1530 AD eruption tapped an hybrid magma assembled by mixing approximately equal proportions of resident andesite and arrival basalt. Mineralogical indicators of the mixing event include An-rich layers in plagioclase, En-rich rims on orthopyroxene and core-rim zonation in magnetite, but overall phenocrysts were little modified during assembly of the hybrid magma. In comparison, matrix glasses were more severely affected. Mixing proceeded essentially by the addition of a mafic melt to the andesite body. The continuous chemical zonation observed in 1530 AD eruption products reflects mixing between three components (mafic melt, silicic melt, phenocryst assemblage). Timescales measured on different eruptive products range from several thousand years (U-Th-Ra disequilibria), 10s days (diffusion modelling in orthopyroxenes) to 10s hours (heterogeneous matrix glasses). Short timescales since mafic recharge, lack of extensive transformations of phenocrysts, continuous whole-rock chemical zonation and predominance of mafic products are all consistent with triggering of the 1530 AD eruption by a major mafic recharge event which originated in the middle to lower Lesser Antilles arc crust.

A Raman calibration for the quantification of SO42– groups dissolved in silicate glasses: Application to natural melt inclusions

Abstract Sulfur is an important volatile element involved in magmatic systems. Its quantification in silicate glasses relies on state-of-the-art techniques such as electronprobe microanalyses (EPMA) or X-ray absorption spectroscopy but is often complicated by the fact that S dissolved in silicate glasses can adopt several oxidation states (S6+ for sulfates or S2− for sulfides). In the present work, we use micro-Raman spectroscopy on a series of silicate glasses to quantify the S content. The database is constituted by 47 silicate glasses of various compositions (natural and synthetic) with S content ranging from 1179 to 13 180 ppm. Most of the investigated glasses have been synthesized at high pressure and high temperature and under fully oxidizing conditions. The obtained Raman spectra are consistent with these fO2 conditions and only S6+ is present and shows a characteristic peak located at ~1000 cm−1 corresponding to the symmetric stretch of the sulfate molecular group (ν1 SO42−

Experimental Simulation of Closed-System Degassing in the System Basalt–H2O–CO2–S–Cl

\begin{array}{} \text{SO}_4^{2-} \end{array}

SolEx: A model for mixed COHSCl-volatile solubilities and exsolved gas compositions in basalt

). The intensity of the ν1 SO42−

The H2O solubility of alkali basaltic melts: an experimental study

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Influence of glass polymerisation and oxidation on micro-Raman water analysis in alumino-silicate glasses

peak is linearly correlated to the parts per million of S6+ determined by EPMA. Using subsequent deconvolution of the Raman spectra, we established an equation using the ratio between the areas of the ν1 SO42−

The carbon dioxide solubility in alkali basalts: an experimental study

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The solubility of sulfur in hydrous basaltic melts

peak and the silicate network species (Qn) in the high-frequency region: ppm S6+=34371ASO42−AQn±609.

Experimental investigation on H2O, CO2, S and Cl degassing at Stromboli: from the magma chamber towards the surface. (Invited)

\begin{array}{} \text{ppm S}^{6+}=34371\frac{A\text{SO}_4^{2-}}{A\text Q^{\text n}}\pm609. \end{array}