Colloquium: Anne Pommier

Abstract: The transport properties of magmas govern their mobility and depend critically on several parameters, such as composition, temperature, pressure, and oxygen fugacity. These parameters affect important Earth and planetary processes, such as subduction, convection, magma crystallization and differentiation, therefore furthering our understanding of the state of crust and upper mantle. Laboratory experiments provide important clues as regards the physics and chemistry of melts, and present implications to different disciplines, such as geophysics, geodynamics, volcanology, and planetary sciences.

Laboratory measurements of electrical conductivity of melts provide insights into the conditions of melt at depth. Measured in the field (magnetotellurics) as well as in the laboratory (impedance spectroscopy), electrical conductivity is a tool with unique potential for bridging different scales of observations. Laboratory electrical measurements on melts and deformed partially molten rocks can be used to interpret electrical conductivity models yielded by field electromagnetic soundings. A conductivity-viscosity model for naturally-occurring melt compositions will be presented, providing a rheological component to the interpretation of field electromagnetic anomalies caused by melt and partially molten rocks. Conductivity measurements can also be used as a probe to infer chemical reactions within magmas, constraining diffusion mechanisms and therefore

documenting kinetics of chemical reactions (e.g. redox changes) in silicate melts.

 

To probe the physical and chemical properties of silicate melts also relates to phase equilibria experiments, with applications regarding in particular the evolution of terrestrial planetary interiors (Mars). Two scientific questions will be addressed adopting this experimental approach: 1) how to investigate the role of water's influence on the melting and differentiation processes of the early Mars; 2) how to investigate the crystallization and differentiation processes of a possible magma ocean. Other applications combining laboratory results, geophysical data analysis and petrological considerations for terrestrial bodies (such as the Moon) will be briefly presented.