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

Sat. May 20, 2017 9:00 AM - 10:30 AM A05 (Tokyo Bay Makuhari Hall)

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:Madhusoodhan Satish-Kumar(Department of Geology, Faculty of Science, Niigata University)

10:00 AM - 10:15 AM

[SIT22-05] Experimental investigation of high-pressure phase transitions in AlOOH and FeOOH

*Masayuki Nishi1,2, Yasuhiro Kuwayama3, Jun Tsuchiya1,2, Taku Tsuchiya1,2 (1.Geodynamics Research Center, Ehime University, 2. Earth-Life Science Institute, Tokyo Institute of Technology, 3.Department of Earth Planetary Science, University of Tokyo)

Keywords:hydrous mineral, high pressure

Hydrogen is transported into deep Earth’s mantle regions as a form of hydrous minerals via subduction of oceanic plates. Recently discovered CaCl2-type hydroxides such as (Mg,Si)OOH phase H, delta-AlOOH, and their solid solutions were reported to have large P–T stability fields that encompass conditions representative of the lower mantle, implying the possibility that surface water may be transported as far as the core–mantle boundary. However, although Epsilon-FeOOH has CaCl2-type structure as well, the solid solution of FeOOH component in CaCl2-type structure has not been studied. Since FeOOH was recently reported to decompose under the lower-mantle conditions to form FeO2 releasing H2, FeOOH could be a key component that strongly affect the stability of CaCl2-type hydroxide. Here, we report the results of in-situ X-ray diffraction and theoretical studies on AlOOH and FeOOH using a laser-heated diamond anvil cell technique at up to ~200 GPa. In contrast to the previous work suggesting the dehydration of FeOOH in the middle of the lower mantle, we report the formation of a pyrite-type FeOOH that is significantly denser than the surrounding mantle and stable to conditions representative of its base. Furthermore, delta-AlOOH and CaCl2-type (Al,Fe)OOH also transform to a pyrite-type structure at higher pressures. Based on these experimental and theoretical results, the stability of hydrous phase in the lower mantle and deep interiors of icy planets will be discussed.