Shock Wave Studies of Liquids in Earth's Core and Mantle

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This award will provide continued support for the Caltech shock wave laboratory to enable the measurement of physical properties of silicate and metallic liquids under conditions matching those in the deepest parts of the Earth. This information is critical to interpreting geophysical observations of the lower mantle and core in terms of composition, temperature, heat flow, and evolution over time. It also allows speculative ideas about an early molten earth (i.e., primordial magma ocean) to be developed into detailed theories. Shock compression is the only experimental method that can simultaneously measure density, pressure, temperature, energy, and sound speed of liquids at such extreme conditions. As part of this study, the team will undertake experimental developments to achieve much higher initial pre-heating temperatures than were previously possible, enabling the direct study of high-melting point liquid compositions most relevant to the primordial magma ocean and lower mantle petrology. The experimental and science agenda includes: 1) building on advances in shock temperature measurement techniques to look at temperatures of shocked silicate liquids, constraining their heat capacity at lower mantle pressures and thereby completing our ability to describe their equation of state in pressure-temperature-density-energy space; 2) furthering the development of new methods to achieve much higher initial pre-heating temperatures than were previously possible to enable the study of the equation of state of ultramafic liquid compositions most relevant to the early magma ocean and lower mantle petrology; and 3) initiating measurements of the sound speeds and densities of liquid iron alloys along actual outer core temperature profiles in order to make the well-defined observed gradient in sound speed with depth in the outer core a new and critical constraint on outer core composition.