Interaction between iron and post‐perovskite at core‐mantle boundary and core signature in plume source region

Abstract

Interaction between the lower mantle and core is essential for understanding the nature of D″ layer at the core‐mantle boundary (CMB). Here, we report the reaction between post‐perovskite (PPv) and metallic iron under the condition of the CMB, for example, 139 GPa and 3000 Kelvin. Analytical transmission electron microscope (ATEM) analysis revealed that significant amount of oxygen up to 6.3 weight percent (wt.%) and silicon up to 4.0 wt.% can be dissolved into molten iron. The dihedral angle between PPv and molten iron is 67 degrees. Thus, a small amount of core metal of about 2 volume percent (vol.%) can be trapped without separation in the PPv region at the CMB. The amount of core metal trapped by this mechanism can produce the isotopic signature of the outer core in the plume source at the base of the lower mantle.

A seismologically consistent compositional model of Earth’s core

“…The solubility of these elements in molten iron coexisting with silicate melt would be several percent (9), even at low pressures. On the other hand, oxygen solubility is much more limited at low pressures, and DAC experiments show that oxygen can be introduced in the core by reaction with the molten mantle at high pressures and temperatures (10,11). Oxygen thus became a natural candidate with the introduction of the "deep magma ocean" models (12-15) of core formation.…”

“…We calculated ρ CMB , ρ ICB , V ϕ,CMB , and V ϕ,ICB for various outer core compositional models in the literature, derived from both experimental and theoretical models (2,7,8,10,11). These are reported in Fig.…”

“…The literature offers a wide range (3,2,7,8,10,11,18,19) of plausible estimates for the light-element composition of the core (SI Appendix, section 1). To constrain these further, we need to assess whether the compositional model for the core matches the seismically observed density and sound velocity of the core.…”

High-pressure experimental geosciences: state of the art and prospects

“…major constituents of rocks at ambient P), have been shown to partition into molten Fe above 70 GPa (Jeanloz and Knittle, 1991) and even more in the P-stability field of the post-perovskite phase (Sakai et al, 2006). It follows that there are likely to be the most abundant light elements in the core, sulphur being a siderophile element at all investigated P-T conditions but too volatile to be present in more than a few % (Dreibus and Palme, 1996).…”

Melting relations in the Fe–S–Si system at high pressure and temperature: implications for the planetary core

“…An investigation of the high-pressure phases of iron alloys also helps us to understand the structure of the solid inner core. Among the candidate light elements in the core, sulfur and silicon are considered as major light element components based on geochemical models (e.g., Allégre et al 1995;Javoy 1995;McDonough 2014) and high-pressure partitioning experiments (e.g., Hillgren et al 2000;Sakai et al 2006). Additionally, some geochemical studies and high-pressure experiments have predicted that sulfur and silicon could be present not only in the core of the Earth but also in the cores of other terrestrial planets such as Mars and Mercury (e.g., Bertka and Fei 1998;Malavergne et al 2010).…”