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SUMMARY:Oxygen distribution in Earth's core - Tetsuya Komabayashi\, Univer
 sity of Edinburgh
DTSTART:20161129T120000Z
DTEND:20161129T130000Z
UID:TALK66957@talks.cam.ac.uk
CONTACT:Sally Gibson
DESCRIPTION:Since Francis Birch (1952) first proposed the idea that Earth
 ’s core should contain light elements\, scientists have been trying to i
 dentify their nature and abundance. This is one of the biggest and long st
 anding arguments about the deep Earth. \n\nIn the seminar I will talk abou
 t my recent high-pressure experiments on pure iron in a newly developed in
 ternally resistive heated diamond anvil cell (DAC) and thermodynamic model
 ling of the system Fe-FeO. I will discuss the implications of these result
 s for the distribution of oxygen in the core of our planet. \n\nFor the pu
 re iron experiments\, we developed a new heating technique in the DAC\, na
 mely internal resistive heating system. This technique produces much highe
 r temperature than external heating systems\, and much more stable heating
  than the conventional laser heating technique. We constrained the pressur
 e (P)-temperature (T) location of a phase transition boundary between the 
 hexagonal close-packed (HCP) structure and face-centred cubic (FCC) struct
 ure. The thermodynamics of melting relations in the system Fe-FeO was inve
 stigated to the outer core-inner core boundary condition from a self-consi
 stent thermodynamic database\, which was evaluated from the latest static 
 high-P-T experiments including our own HCP-FCC boundary. From the Gibbs fr
 ee energy for the Fe-FeO liquids\, I calculated the density\, sound veloci
 ty\, and isentropic temperature gradient of a hypothetical oxygen-bearing 
 outer core. \n\nUnder the outer core conditions\, the addition of oxygen r
 educes the compressional wave velocity of iron liquid\, moving it away fro
 m seismologically constrained values. An overall O-rich bulk outer core mo
 del is thus excluded. Seismological observations however\, suggest the pre
 sence of a low-velocity layer with a thickness of 60-70 km at the top of t
 he outer core. The origin of such a low-velocity layer can be explained by
  an enrichment of oxygen\, which might be a consequence of chemical intera
 ctions between the core and mantle.\n
LOCATION:Tilley Lecture Theatre\, Department of Earth Sciences
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