Yann Morizet

The influence of H2O and CO2 on the glass transition temperature: insights into the effects of volatiles on magma viscosity

CO 2 can play an important role in eruptive processes; in particular, it has the potential to reach saturation at lower concentrations than H 2 O and initiate degassing. The effect of such CO 2 loss on magma viscosity is not well constrained, especially compared to the established effects of H 2 O loss. In terms of understanding the CO 2 solubility mechanism, recent spectroscopic studies have shown that CO 2 speciation is strongly temperature dependent and that CO 2 speciation preserved in quenched glasses below T g is different from the true CO 2 speciation observed in the melts. However, the effect of CO 2 on the glass transition temperature, and by inference the viscosity, has not been previously established. In this study, calorimetric measurements were conducted on synthetic H 2 O- and CO 2 -bearing phonolite and jadeite glasses in order to investigate the volatile’s effect on the glass transition interval, by defining a single glass transition temperature ( T g onset ). The samples were synthesised in a piston-cylinder apparatus between 1300 and 1550 °C, at 1.0 to 2.5 GPa, and contained up to 2.29 wt.% CO 2 and up to 5.49 wt.% H 2 O. For both compositions, H 2 O has a large effect in reducing T g onset , but CO 2 appears to have little or no effect. For the entire range of H 2 O contents, T g onset decreases exponentially with H 2 O content from 870 to 523 K and 1036 to 636 K for phonolite and jadeite, respectively, regardless of the CO 2 content. No measurable effect of CO 2 on T g onset was observed. These results suggest that compared to H 2 O, CO 2 contributes little to changes in the physical properties of the melt. They also provide strong evidence for the decoupling of CO 2 speciation from the bulk silicate melt structural relaxation process at T g .

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.

Solid-state NMR analysis of Fe-bearing minerals: implications and applications for Earth sciences

Solid-state nuclear magnetic resonance (NMR) is commonly used in the study of solid structures in Earth sciences; however, it suffers from the impossibility to analyse solid structures containing ferromagnetic particles or paramagnetic elements. We have attempted to decipher the effect of (1) ferromagnetic particles (Fe- Ti-bearing mineral phase) and (2) paramagnetic elements (Fe, Cr, Ni) on the signature of diamagnetic elements ( 1 H, 29 Si, 27 Al) in natural clino- and orthopyroxene from peridotite. The results obtained on these natural minerals have been compared with results obtained for a synthetic mixture of kaolinite + magnetite. The 29 Si, 27 Al Echo-MAS NMR spectra acquired for pyroxenes show signatures that are consistent with previous data. Weak additional anomalous peaks are detected in 29 Si spectra. Both elements show a broadening in the spectra, which is commonly observed when paramagnetic elements are present. The perturbations induced by paramagnetic elements are the result of several interactions: (1) pseudocontact shift and (2) Fermi contact shift. 1 H Echo-MAS NMR spectra for pyroxenes are dramatically affected by the presence of ferromagnetic impurities and are chemical shifted beyond the known range for 1 H in solids. The effect of ferromagnetic particles is also confirmed by the results obtained for the kaolinite + magnetite mixture showing increasing perturbation with increasing magnetite content. We suggest that the presence of paramagnetic elements and/or ferromagnetic particles is only weakly affecting the 29 Si and 27 Al NMR spectra. Thus, new perspectives on the use of NMR technique for mineralogy and geochemistry are envisaged.

17 O NMR evidence of free ionic clusters Mn+ CO3 2− in silicate glasses: Precursors for carbonate-silicate liquids immiscibility

Abstract Carbon dioxide is a ubiquitous component of low-silica melts such as kimberlites or melilitites. It is currently assumed that CO2 molecules dissolving in low-silica melts as carbonate groups (CO32−)

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

\rm(CO_{3}^{2-})

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

induce a strong polymerization of the silicate network; however, the exact molecular configuration of this dissolution mechanism is still debated. Using 17O MAS NMR spectroscopy, we have investigated the carbonate molecular environment in a series of synthesized low-silica (31–41 wt% SiO2), CO2-bearing (from 2.9 to 13.2 wt% CO2) silicate glasses analogous to melilitites and kimberlites. With the selective {13C}-, {27Al}-, and {29Si}-17O J HMQC NMR method, we show that CO2 dissolved in the studied low-silica glasses is totally disconnected from the silicate network, forming free ionic clusters (FIC) Mn+ (CO32−)

C–O–H fluid solubility in haplobasalt under reducing conditions: An experimental study

\rm(CO_{3}^{2-})

Raman study of methane clathrate hydrates under pressure: new evidence for the metastability of structure II

with Mn+, a charge compensating cation. The Mn+ (CO32−)

Phase equilibria in the H2O–CO2 system between 250–330 K and 0–1.7 GPa: Stability of the CO2 hydrates and H2O-ice VI at CO2 saturation

\rm(CO_{3}^{2-})

Raman quantification factor calibration for CO-CO2 gas mixture in synthetic fluid inclusions: Application to oxygen fugacity calculation in magmatic systems.

FIC are considered as precursors to immiscibility in between carbonate and silicate liquids. Observed in all studied compositions, we suggest that this immiscibility can be produced from moderately to strongly depolymerized silicate melt compositions.