HR: 0800h
AN: MR31B-0365    [Abstracts]
TI: Fe-Mg partitioning between perovskite, post-perovskite, and ferropericlase at the lowermost mantle
AU: * Sakai, T
EM: sakai@ganko.tohoku.ac.jp
AF: International Advanced Research and Education Organization, Tohoku University, Aoba-ku, Aramaki, Aoba, Sendai, 980-8578, Japan
AU: Ohtani, E
EM: ohtani@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology, and Economic Geology, Tohoku University, Aoba-ku, Aramaki, Aoba, Sendai, 980-8578, Japan
AU: Miyahara, M
EM: miyahara@ganko.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology, and Economic Geology, Tohoku University, Aoba-ku, Aramaki, Aoba, Sendai, 980-8578, Japan
AU: Nishijima, M
EM: ni_shi@imr.tohoku.ac.jp
AF: Institute for material Research, Tohoku University, Aoba-ku, Katahira, Sendai, 980-9877, Japan
AU: Terasaki, H
EM: terasaki@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology, and Economic Geology, Tohoku University, Aoba-ku, Aramaki, Aoba, Sendai, 980-8578, Japan
AU: Kondo, T
EM: tdskondo@ess.sci.osaka-u.ac.jp
AF: Graduate School of Science, Osaka University, 1-1 Mashkaneyama, Toyonaka, Osaka, 560- 0043, Japan
AU: Kikegawa, T
EM: kikegawa@post.kek.jp
AF: Photon Factory, 1-1 Ohho, Tsukuba, 305-0801, Japan
AU: Hirao, N
EM: hirao@spring8.or.jp
AF: Japan Synchrotron Radiation research Institute, 1-1-1 Kouto Sayo, Hyogo, 679-5198, Japan
AU: Ohishi, Y
EM: ohishi@spring8.or.jp
AF: Japan Synchrotron Radiation research Institute, 1-1-1 Kouto Sayo, Hyogo, 679-5198, Japan
AB: The lower mantle consists mainly of iron-bearing magnesium silicate perovskite and ferropericlase. The Fe-Mg partition coefficient between these minerals is important to understand the chemical and physical properties of the mantle. The lowermost 200 km of the mantle is called D" layer and it is considered to be a thermal and chemical boundary layer between the silicate mantle and outer core. Recent high pressure studies [e.g., Murakami et al., 2004] revealed that (Mg, Fe)SiO3 perovskite transformed to post-perovskite phase at the pressure and temperature conditions of D" layer. In this study, high pressure and high temperature partitioning experiments were performed up to 140 GPa at 2000 K using a laser heated diamond anvil cell (LHDAC). Powdered or single crystalline Al-free San Carlos olivine (Mg0.88, Fe0.12)2SiO4 was used as a starting material in order to avoid complicated compositional effects. The starting material was embedded in sodium chloride which is pressure medium. Pressures were determined by both the ruby fluorescence method [Mao et al., 1978] and the Raman shift of the first-order Raman spectra of diamond anvil [Akahama and Kawamura, 2004]. Temperatures were measured by spectroradiometric method. The recovered samples were analyzed using the technique of combination of FIB and ATEM (JEOL JEM-3000F (FEG TEM-STEM)). The result shows that post- perovskite phase exhibits very small iron content, Fe# = 0.01 at 140 GPa and 2000 K. Therefore, the partition coefficient was K = 0.03, which indicates that iron prefers ferropericlase strongly rather than post-perovskite phase, which is consistent with the prediction of the ab initio calculation [Iitaka et al., 2004], and the high-spin/low- spin transition arguments of ferropericlase [Badro et al., 2003]. Kobayashi et al. (2005) showed higher partitioning coefficient of K= 0.30 in spite of the lower temperature condition of 1600 K compared to the present experiment. They reported that significant iron depletion occurred in the sample heated at the high pressure condition, i.e., bulk Fe# (FeO/(MgO+FeO) in molar ratio) reduced to 0.09 from 0.12. On the other hand, the bulk iron content in the present experiment conducted at 140 GPa and 2000 K does not show a significant iron depletion. Therefore, the significant difference in the partition coefficients between the present result and that by Kobayashi et al may be caused by the compositional dependency of the partitioning behavior between post- perovskite and ferropericlase. Further study is necessary to clarify the compositional effect together with the effect of the spin transition on the partitioning behavior.
DE: 3612 Reactions and phase equilibria (1012, 8412)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting