In addition to temperature, pressure and main chemical components, volatiles exert a strong influence on the physical properties of magmas. In particular, water plays a fundamental role in the dynamics and evolution of magmas in the deep interior and during volcano eruption. However, water speciation in silicate melts is not fully understood. Infrared spectroscopy had provided some valuable information about the H2O/OHspeciation. We know that this speciation is a function of temperature and water contents of melts. It can be very interesting to know it from in situ experiments. This can be done using Raman spectroscopy. Raman spectra are composed of i) a low-wavenumber region which corresponds to vibrations of the silicate network (0-1500 cm-1), and ii) a high-wavenumber region which correspond to the OH- stretching vibration and H2O molecular vibration (3100-3750 cm-1). We have performed a first set of in situ experiments using a micro-furnace at ambient pressure. We have observed an evolution of the high-wavenumber region as a function of time and temperature. New Raman peaks can be distinguished, particularly near 3650-3700 cm-1. In this communication, we will present our first results on this subject and then discuss them in terms of relation between water and the silicate network.
Water speciation in silicate melts: an high temperature Raman spectroscopy study.
MORETTI, Roberto;
2010
Abstract
In addition to temperature, pressure and main chemical components, volatiles exert a strong influence on the physical properties of magmas. In particular, water plays a fundamental role in the dynamics and evolution of magmas in the deep interior and during volcano eruption. However, water speciation in silicate melts is not fully understood. Infrared spectroscopy had provided some valuable information about the H2O/OHspeciation. We know that this speciation is a function of temperature and water contents of melts. It can be very interesting to know it from in situ experiments. This can be done using Raman spectroscopy. Raman spectra are composed of i) a low-wavenumber region which corresponds to vibrations of the silicate network (0-1500 cm-1), and ii) a high-wavenumber region which correspond to the OH- stretching vibration and H2O molecular vibration (3100-3750 cm-1). We have performed a first set of in situ experiments using a micro-furnace at ambient pressure. We have observed an evolution of the high-wavenumber region as a function of time and temperature. New Raman peaks can be distinguished, particularly near 3650-3700 cm-1. In this communication, we will present our first results on this subject and then discuss them in terms of relation between water and the silicate network.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
