The structure of silicate magmas, melts and glasses

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Understanding the behaviour of molten rock or melts under the conditions found deep in the Earth is important if we are to understand how the Earth formed, how magmas evolve, and their chemical and dynamical behaviour below the surface of the Earth. I am studying such molten materials under these conditions. I investigate how the structure of such liquids change under ambient conditions (using quenched liquids or glasses) as well as extreme conditions. I primarily use state-of-the-art synchrotron based techniques in addition to techniques such as Raman spectroscopy. In particular, experimental beamlines at the Canadian Light Source and other international light sources are used to study the environment around elements commonly found in geological melts and magmas such as Si, O, Al, alkalis and alkaline-earths. In collaboration with a number of international research groups we probe the structure of simple synthetic melts of geological interest, including model basalts and granites. The findings of these studies greatly enhance our understanding of how the Earth initially formed, as well as the physical and chemical behaviour melts. We recently showed free oxygen (O2-) occurs in simple melts and is a critical component for the melting and crystallization of chain and sheet silicates. Our proposed melting model (the first in over 100 years) explains how these minerals melt and crystallize. Furthermore studieson the high frequency region of Raman spectra of glasses and melts show so called "Q species" vibrations have consistent and predictable peaks positions and shapes. Extra peaks observed in the spectra are due to the presence of MBOs (bridging oxygens with an alkali or alkaline earth "attached"). These "species" have not been considered in previous studies on silicate glasses and melts, rendering nearly all previous Raman studies of glasses and melts moot. These MBO vibrations must be considered when fitting spectroscopic data. The current proposal focusses primarily on the structural role of light elements and oxygen in glasses and melts and builds on these findings. I intend to continue investigating the role of O2- in melting reactions with an emphasis on considering the presence of Al. In the melting studies it is clear that melts initially polymerize before depolymerizing and crystallizing. I will investigate why they initially polymerize and if this somehow "stabilizes" the melt. In order to better understand the behaviour of the MBO and Q species in alkali silicate glasses I will investigate select compositions in small alkali increments (0-15 mol% and 30-50 mol% in 1 mol% steps) using Raman spectroscopy in order to elucidate the explicit nature of the relationship between peak positions and shapes with composition.