Melting behavior of the lower-mantle ferropericlase across the spin crossover

Implication for the ultra-low velocity zones at the lowermost mantle

Suyu Fu, Jing Yang, Youjun Zhang, Jiachao Liu, Eran Greenberg, Vitali B. Prakapenka, Takuo Okuchi, Jung Fu Lin

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Preferential iron partitioning into melt during melting and crystallization of lower mantle minerals – bridgmanite and ferropericlase – can play a critical role in our understanding of the origin of the early Earth and its evolution to form chemically and seismically distinct regions in the present lowermost mantle. Of particular interest is the consequence of iron spin crossover in ferropericlase on the physical and chemical properties of the molten materials under relevant pressure–temperature (P–T) conditions of the lowermost mantle. However, the spin crossover in liquid (Mg, Fe)O and its effects on melting curves, iron partitioning, melt density – and thus the evolution of an early basal magma ocean – remain poorly studied. Here we conducted high P–T melting experiments on ferropericlase with a starting composition of (Mg0.86Fe0.14)O using synchrotron X-ray diffraction up to ∼120 GPa and ∼5400 K in laser-heated diamond anvil cells, together with chemical analyses on quenched samples using focused ion beam and energy dispersive spectroscopy technique. An ideal solid solution model could be satisfactorily used to fit the experimental data of the liquidus and solidus of (Mg, Fe)O for pure high-spin (HS, below ∼83 GPa), and low-spin (LS, above ∼120 GPa) states, respectively. The experimental solidus and liquidus at 99 GPa and ∼4000–5200 K strongly deviate from ideal solid solution behavior for pure HS and LS states alone, but can be qualitatively explained using a thermodynamics model for a mixture of HS and LS states across the spin crossover. We found that LS (Mg, Fe)O exhibits ∼6–8% lower solidus and liquidus temperature than its HS counterpart. Furthermore, our results show that iron preferentially partitions into melt within the spin crossover to generate iron-rich LS melt. Such iron-rich LS (Mg, Fe)O is ∼27(±5)% denser than materials expected for lowermost mantle and could potentially persist as residual melt in the lowermost mantle at the late stage of magma ocean crystallization. Modeled results indicate that the existence of the dense, iron-rich LS (Mg, Fe)O melt in the lowermost mantle could provide plausible explanations for characteristic seismological signatures of ultra-low velocity zones (ULVZs).

Original languageEnglish
Pages (from-to)1-9
Number of pages9
JournalEarth and Planetary Science Letters
Volume503
DOIs
Publication statusPublished - Dec 1 2018

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low velocity zone
lower mantle
low speed
crossovers
Earth mantle
Melting
Iron
melting
mantle
iron
melt
solidus
liquidus
Crystallization
solid solution
magma
Solid solutions
oceans
crystallization
solid solutions

Keywords

  • ferropericlase
  • lower mantle
  • melting behavior
  • spin crossover

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Melting behavior of the lower-mantle ferropericlase across the spin crossover : Implication for the ultra-low velocity zones at the lowermost mantle. / Fu, Suyu; Yang, Jing; Zhang, Youjun; Liu, Jiachao; Greenberg, Eran; Prakapenka, Vitali B.; Okuchi, Takuo; Lin, Jung Fu.

In: Earth and Planetary Science Letters, Vol. 503, 01.12.2018, p. 1-9.

Research output: Contribution to journalArticle

Fu, Suyu ; Yang, Jing ; Zhang, Youjun ; Liu, Jiachao ; Greenberg, Eran ; Prakapenka, Vitali B. ; Okuchi, Takuo ; Lin, Jung Fu. / Melting behavior of the lower-mantle ferropericlase across the spin crossover : Implication for the ultra-low velocity zones at the lowermost mantle. In: Earth and Planetary Science Letters. 2018 ; Vol. 503. pp. 1-9.
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