Giada Iacono-Marziano

Carbonatite Melts and Electrical Conductivity in the Asthenosphere

Electrically conductive regions in Earths mantle have been interpreted to reflect the presence of either silicate melt or water dissolved in olivine. On the basis of laboratory measurements, we show that molten carbonates have electrical conductivities that are three orders of magnitude higher than those of molten silicate and five orders of magnitude higher than those of hydrated olivine. High conductivities in the asthenosphere probably indicate the presence of small amounts of carbonate melt in peridotite and can therefore be interpreted in terms of carbon concentration in the upper mantle. We show that the conductivity of the oceanic asthenosphere can be explained by 0.1 volume percent of carbonatite melts on average, which agrees with the carbon dioxide content of mid-ocean ridge basalts.

Role of non-mantle CO2 in the dynamics of volcano degassing: The Mount Vesuvius example

Mount Vesuvius, Italy, quiescent since A.D. 1944, is a dangerous volcano currently characterized by elevated CO2 emissions of debated origin. We show that such emissions are most likely the surface manifestation of the deep intrusion of alkalic-basaltic magma into the sedimentary carbonate basement, accompanied by sidewall assimilation and CO2 volatilization. During the last eruptive period (1631–1944), the carbonate-sourced CO2 made up 4.7–5.3 wt% of the vented magma. On a yearly basis, the resulting CO2 production rate is comparable to CO2 emissions currently measured in the volcanic area. The chemical and isotopic composition of the fumaroles supports the predominance of this crust-derived CO2 in volatile emissions at Mount Vesuvius.

Quantification of dissolved CO2 in silicate glasses using micro-Raman spectroscopy

Abstract This study investigates the potential use of confocal micro-Raman spectroscopy for the quantification of CO2 in geologically relevant glass compositions. A calibration is developed using a wide range of both natural and synthetic glasses that have CO2 dissolved as carbonate (CO32-) in the concentration range from 0.2 to 16 wt%. Spectra were acquired in the 200 and 1350 cm-1 frequency region that includes the ν1 Raman active vibration for carbonate at 1062-1092 cm-1 and the intensity of this peak is compared to various other peaks representing the aluminosilicate glass structure. The most precise and accurate calibration is found when carbonate peaks are compared to aluminosilicate spectral features in the high-frequency region (HF: 700-1200 cm-1), which can be simulated with several Gaussian peaks, directly related to different structural species in the glass. In some samples the “dissolved” CO32- appears to have two different Raman bands, one sharper than the other. This may be consistent with previous suggestions that CO32- has several structural environments in the glass, and is not related to any precipitation of crystalline carbonate from the melt during quenching. The calibration derived using the HF peaks appears linear for both the full range of glass composition considered and the range of CO2 concentrations, even when multiple carbonate peaks are involved. We propose the following, compositionally independent linear equation to quantify the CO2 content in glass with micro-Raman spectroscopy wt% CO2 = 15.17 × CO3/HF where CO3/HF is the area ratio of the fitted ν1 carbonate peak(s) at 1062-1092 cm-1 to the remaining area of the fitted aluminosilicate envelope from 700-1200 cm-1. This is similar to the Raman calibration developed for water, but is complicated by the overlapping of these two fitted components. Using error propagation, we propose the calibration accuracy is better than ±0.4 wt% CO2 for our data set. The ν1 Raman peak position for carbonate is not constant and appears to be correlated with the density of the melt (or glass) in some way rather than the chemical composition.

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−

New experimental data and semi-empirical parameterization of H2O–CO2 solubility in mafic melts

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The H2O solubility of alkali basaltic melts: an experimental study

). The intensity of the ν1 SO42−

Geochemical evidence for mixing between fluids exsolved at different depths in the magmatic system of Mt Etna (Italy)

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Noble gas solubilities in silicate melts: New experimental results and a comprehensive model of the effects of liquid composition, temperature and pressure

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−

Extremely reducing conditions reached during basaltic intrusion in organic matter-bearing sediments

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The redox geodynamics linking basalts and their mantle sources through space and time

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