Temperature of Earth's core constrained from melting of Fe and Fe0.9Ni0.1 at high pressures

Abstract

The melting points of fcc-and hcp-structured Fe 0.9 Ni 0.1 and Fe are measured up to 125 GPa using laser heated diamond anvil cells, synchrotron Mössbauer spectroscopy, and a recently developed fast temperature readout spectrometer. The onset of melting is detected by a characteristic drop in the time-integrated synchrotron Mössbauer signal which is sensitive to atomic motion. The thermal pressure experienced by the samples is constrained by X-ray diffraction measurements under high pressures and temperatures. The obtained best-fit melting curves of fcc-structured Fe and Fe 0.9 Ni 0.1 fall within the wide region bounded by previous studies. We are able to derive the γ-ǫ-l triple point of Fe and the quasi triple point of Fe 0.9 Ni 0.1 to be 110±5 GPa, 3345±120 K and 116±5 GPa, 3260±120 K, respectively. The measured melting temperatures of Fe at similar pressure are slightly higher than those of Fe 0.9 Ni 0.1 while their one sigma uncertainties overlap. Using previously measured phonon density of states of hcp-Fe, we calculate melting curves of hcp-structured Fe and Fe 0.9 Ni 0.1

Sound velocity and density of magnesiowüstites: Implications for ultralow‐velocity zone topography

“…Looking ahead, better knowledge of temperature at the core-mantle boundary is important, as estimates of the CMB temperature fall right around the melting point of very FeO rich assemblages [Zhang et al, 2016]. Iron enrichment has the potential to explain large velocity drops at the base of the mantle, and the consequences of the physical state of this boundary layer on mantle evolution, core-mantle interaction, and magnetic coupling have yet to be fully explored.…”

“…The storage ring was operated in low-emittance top-up mode with 24 bunches separated by 153 ns. In these experiments, X-rays are monochromatized to 1 meV bandwidth [Toellner, 2000], scanned around the nuclear resonance energy of 14.4125 keV, and focused to 10 × 11μm 2 [Zhang et al, 2016] on an 57 Fe-containing sample. The delayed emission of nuclear resonant fluorescence radiation into a large solid angle is observed using avalanche photodiode detectors [Sturhahn and Jackson, 2007].…”

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

“…On the outer core side of the ICB, κ is estimated to be 104-131 W/m · K relying on the current uncertainties in ICB temperatures (5,500-6,000 K; e.g., Anzellini et al, 2013). On the core side of the CMB, we estimate κ to be between 65 and 73 W/m · K assuming that temperatures at CMB are in the range 4,000-4,500 K (e.g., Badro et al, 2014;Zhang, Jackson, et al, 2016) and ρ of~150 μΩcm. These estimates are in a reasonable agreement with the lower end of the recent theoretically and experimentally obtained values (e.g., Gomi et al, 2013Gomi et al, , 2016Gomi & Hirose, 2015;de Koker et al, 2012;Pozzo et al, 2012Pozzo et al, , 2013Seagle et al, 2013;Xu et al, 2018).…”

Melting at the Edge of a Slab in the Deepest Mantle

“…There is a large amount of uncertainty in temperature at the CMB (Anzellini et al, 2013;Zhang et al, 2016), but, of the possible lower mantle constituents, subducted mid-ocean ridge basalt (MORB), is predicted to have the lowest melting temperature (Andrault et al, 2014;Pradhan et al, 2015). As the D″ region may be the final resting place of subducted slabs (Fukao et al, 2001;Grand et al, 1997), partial melting of MORB has been suggested as a source of partially molten ULVZs.…”