Grain growth of ε-iron: Implications to grain size and its evolution in the Earth's inner core

Daisuke Yamazaki, Noriyoshi Tsujino, Akira Yoneda, Eiji Ito, Takashi Yoshino, Yoshinori Tange, Yuji Higo

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Knowledge of grain growth rate of ε-iron can put constraint on estimation of the grain size in the inner core. We determined grain growth rate of ε-iron at ∼55 GPa and 1200–1500 K by means of in-situ X-ray diffraction observation to be Gn−G0 n=kt, where G (m) is the grain size at time t (s), G0 (m) is the initial grain size, n is growth exponent (fixed to 2) and k is the growth constant expressed as k=k0exp⁡(−H/RT) with log k0(mn/s)=−5.8(±2.4) and activation enthalpy H=221(±61) kJ/mol, and R is the gas constant and T is the absolute temperature. Extrapolation of the grain growth law of ε-iron to the inner core conditions suggests that the grain size in the inner core is in a range from several hundred meters to several kilometers, which is intermediate among the previous estimations, and hence the dominant deformation mechanism is considered to be Harper–Dorn creep rather than diffusion creep as pointed out by the previous work. This indicates the relatively uniform viscosity in the entire inner core.

Original languageEnglish
Pages (from-to)238-243
Number of pages6
JournalEarth and Planetary Science Letters
Volume459
DOIs
Publication statusPublished - Feb 1 2017

Keywords

  • grain growth
  • inner core
  • ε-iron

ASJC Scopus subject areas

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

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