High-Pressure, High-Temperature Equations of State for Fe, Ni, and Co Silicates, Oxides and Metals: Constructing a Deep Earth Electrochemical Series.

Abstract:

Redox thermodynamics of core and mantle materials at planetary interior conditions govern which elements tend to be oxidized and which tend to be reduced by their relative positions on a planetary-interior electrochemical series. Here we present integrated results of equation of state measurements for Fe, Co, and Ni silicates, oxides and metals, showing relative energy differences between oxidized and reduced phases. Measurements of high pressure and temperature equations of state were performed using X-ray diffraction in the laser-heated diamond anvil cell. Using our data and others’, we measure equations of state of Fe, Co and Ni metals, oxides and silicates, showing their relative redox potentials as a function of pressures and temperatures.

Our results for the relative oxidation energetics of Co and Ni ringwoodite silicates with respect to their metals suggests a crossover between the relative oxidation potentials of Ni and Co at mid-mantle pressures and temperatures (Figure 1). This result agrees with our predictions of the metal-oxide systems, and mirrors measurements of pressure-dependent metal-silicate distribution coefficients.