Viscosity of Evolving Magmas: A case study of the Glass House Mountains, Australia

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The volcanoes known as the Glass House Mountains (GHM) illustrate a compositional series of magmas produced by fractional crystallisation of a magma chamber which is associated with the Australian continent passing over a mantle plume 26 million years ago. There is little information on the emplacement of these magmas or the temperature of the magma chamber. As a first approach to addressing the occurrence of the Glass House Mountains volcanic plugs and the processes occurring in the magma chamber, the viscosity of the different magma compositions will be determined. The compositional series provide a textbook case for the determination of viscosity of a magma chamber undergoing fractional crystallisation and discharge. The rheology of the Glass House Mountains magmas will be determined at high viscosity conditions using the micro-penetration technique. The viscosities will be extrapolated to low viscosity conditions using heat capacity data and the Adam-Gibbs relationship between viscosity and configurational entropy and temperature.