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CATEGORIES:Department of Earth Sciences Seminars (downtown)
SUMMARY:Oxygen distribution in Earth's core - Tetsuya Koma
 bayashi\, University of Edinburgh
DTSTART;TZID=Europe/London:20161129T120000
DTEND;TZID=Europe/London:20161129T130000
UID:TALK66957AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/66957
DESCRIPTION:Since Francis Birch (1952) first proposed the idea
  that Earth’s core should contain light elements\,
  scientists have been trying to identify their nat
 ure and abundance. This is one of the biggest and 
 long standing arguments about the deep Earth. \n\n
 In the seminar I will talk about my recent high-pr
 essure experiments on pure iron in a newly develop
 ed internally resistive heated diamond anvil cell 
 (DAC) and thermodynamic modelling of the system Fe
 -FeO. I will discuss the implications of these res
 ults for the distribution of oxygen in the core of
  our planet. \n\nFor the pure iron experiments\, w
 e developed a new heating technique in the DAC\, n
 amely internal resistive heating system. This tech
 nique produces much higher temperature than extern
 al heating systems\, and much more stable heating 
 than the conventional laser heating technique. We 
 constrained the pressure (P)-temperature (T) locat
 ion of a phase transition boundary between the hex
 agonal close-packed (HCP) structure and face-centr
 ed cubic (FCC) structure. The thermodynamics of me
 lting relations in the system Fe-FeO was investiga
 ted to the outer core-inner core boundary conditio
 n from a self-consistent thermodynamic database\, 
 which was evaluated from the latest static high-P-
 T experiments including our own HCP-FCC boundary. 
 From the Gibbs free energy for the Fe-FeO liquids\
 , I calculated the density\, sound velocity\, and 
 isentropic temperature gradient of a hypothetical 
 oxygen-bearing outer core. \n\nUnder the outer cor
 e conditions\, the addition of oxygen reduces the 
 compressional wave velocity of iron liquid\, movin
 g it away from seismologically constrained values.
  An overall O-rich bulk outer core model is thus e
 xcluded. Seismological observations however\, sugg
 est the presence of a low-velocity layer with a th
 ickness of 60-70 km at the top of the outer core. 
 The origin of such a low-velocity layer can be exp
 lained by an enrichment of oxygen\, which might be
  a consequence of chemical interactions between th
 e core and mantle.\n
LOCATION:Tilley Lecture Theatre\, Department of Earth Scien
 ces
CONTACT:Sally Gibson
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