JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT22] [EE] Interaction and Coevolution of the Core and Mantle in the Earth and Planets

Mon. May 22, 2017 3:30 PM - 5:00 PM Convention Hall B (International Conference Hall 2F)

convener:Taku Tsuchiya(Geodynamics Research Center, Ehime University), Hidenori Terasaki(Graduate School of Science, Osaka University), Madhusoodhan Satish-Kumar(Department of Geology, Faculty of Science, Niigata University), Tetsuo Irifune(Geodynamics Research Center, Ehime University), John Hernlund(Earth-Life Science Institute, Tokyo Institute of Technology), Eiji Ohtani(Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University), Chairperson:Taku Tsuchiya(Geodynamics Research Center, Ehime University)

3:30 PM - 3:45 PM

[SIT22-37] Iron-carbonate interaction in the lower mantle and at the core-mantle boundary

★Invited papers

*Konstantin Litasov1, Naira Martirosyan1, Hiroaki Ohfuji2, Sergey Lobanov3, Alexander Goncharov3 (1.V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia, 2.Geodynamic Research Center, Ehime University, Matsuyama, Japan, 3.Geophysical Laboratory, Carnegie Institution of Washington, Washington DC, USA)

Keywords:Mg-carbonate, carbide, diamond, lower mantle, core-mantle boundary

The presence of carbonates in the deep Earth strongly depends on the oxygen fugacity, controlled by oxidation state of iron in minerals and melts. A large part of the lower mantle can be significantly reduced with detectable amount of Fe0. Therefore, subducted carbonates would interact with Fe0 dispersed in the ambient mantle. However, the mechanism of this interaction remains controversial. We investigated the MgCO3–Fe0 system at 70–145 GPa and 800–2600K using in situ X-ray diffraction in a diamond anvil cell. MgCO3 crystals and Fe foil (99,9%) were used as the starting materials. Formation of wustite (FeO), ferropericlase (Mg0.6Fe0.4)O, carbide (Fe7C3) and diamond was observed. Three different modifications of FeO were detected: B1 at T = 1100–2600K and 70–145 GPa, rB1 at T<1100 K and P<136GPa; and B8 at P = 143-145 GPa. Interestingly, we observed coexistence of wüstite and ferropericlase, which may suggest an existence of immiscibility gap in FeO-MgO system at P > 70 GPa. Mg-carbonate reduction can be presented by following reaction: 6MgCO3 + 19Fe = 8FeO + 10(Mg0.6Fe0.4)O + Fe7C3 + 3C. The formation of diamond was confirmed by TEM study of run products at 100-145 GPa. The studied carbonate-iron reaction supports formation of the (Fe,Mg)O, carbide and diamond in the lower mantle and at the Earth’s core-mantle boundary indicating that subducted carbonates transported to the core-mantle boundary would be reduced to carbide or diamond. Similar reaction may occur in the Fe-CaMg-carbonate systems. Using these data we propose that core-mantle boundary is important to produce diamond and Fe-carbide.