HEMI Seminar: Paul Asimow (Caltech)

 Towards a comprehensive thermal equation of state for silicate liquids at lower mantle pressure (and beyond)

Paul Asimow is the Eleanor and John R. McMillan professor of Geology and Geochemistry at Caltech and the principal investigator of the Lindhurst Laboratory for Experimental Geophysics. He has a bachelor’s degree in Geological Science from Harvard College and a Ph.D. in geology from Caltech. After a postdoc at the Lamont-Doherty Geological Observatory of Columbia University, he returned to Caltech as assistant professor and has been there ever since. His research interests are in igneous petrology and high-pressure mineral physics, especially the properties of liquids in deep planetary interiors and their consequences for dynamical and differentiation processes. His approaches combine static and shock wave compression, thermodynamic modeling, and analysis of magmatic rocks from Earth and meteorites.

Understanding the complete thermal equation of state of silicate melts at pressures above ~100 GPa is essential for describing the evolution of early terrestrial magma oceans, for interpreting the state of the modern core mantle boundary, and for speculating about the interior structure of super-earth exoplanets. The EoS must be accurate enough to assess the the density difference between melts and their coexisting solids and to extrapolate free energies as a function of composition, temperature, and pressure well enough to model phase equilibria. I am extending my database of direct shock wave measurements of P-V-E points from pre-heated silicate liquids by measuring shock temperature and bulk sound velocity in the liquid in the shock state. These define the heat capacity at high pressure and a direct, local measurement of the Grüneisen parameter. Improved knowledge of heat capacity and Grüneisen parameter allow the shock EoS to be confidently applied to crystal/liquid buoyancy and phase equilibrium calculations at actual lower mantle liquidus and solidus temperatures. Long term, these data can be used to assess whether a formulation of the Helmholtz free energy (in V, T space) is in fact the best way to fit the EoS of a silicate liquid or whether an enthalpy formulation (in P, S space) works better.