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Publication Detail
Effect of water in depleted mantle on post-spinel transition and implication for 660 km seismic discontinuity
  • Publication Type:
    Journal article
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  • Authors:
    Ghosh S, Ohtani E, Litasov KD, Suzuki A, Dobson D, Funakoshi K
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    affiliation: Ghosh, S (Reprint Author), ETH, Inst Geochem & Petrol, CH-8092 Zurich, Switzerland. Ghosh, Sujoy; Ohtani, Eiji; Litasov, Konstantin D.; Suzuki, Akio, Tohoku Univ, Dept Earth & Planetary Mat Sci, Sendai, Miyagi 9808578, Japan. Ghosh, Sujoy, ETH, Inst Geochem & Petrol, CH-8092 Zurich, Switzerland. Litasov, Konstantin D., Novosibirsk State Univ, Novosibirsk 630090, Russia. Litasov, Konstantin D., VS Sobolev Inst Geol & Mineral SB RAS, Novosibirsk 630090, Russia. Dobson, David, UCL, Dept Earth Sci, London WC1E 6BT, England. Funakoshi, Kenichi, Japan Synchrotron Radiat Res Inst, Kouto, Japan. keywords: post-spinel transition; ringwoodite; Mg-perovskite; transition zone; water; 660 km discontinuity keywords-plus: EQUATION-OF-STATE; X-RAY-DIFFRACTION; ELECTRICAL-CONDUCTIVITY; EARTHS MANTLE; SYSTEM MG2SIO4-FE2SIO4; 660-KILOMETER DISCONTINUITY; POSTSPINEL TRANSFORMATION; GEOPHYSICAL IMPLICATIONS; PHASE-TRANSITIONS; HIGH-PRESSURE research-areas: Geochemistry & Geophysics web-of-science-categories: Geochemistry & Geophysics author-email: sujoy.ghosh@erdw.ethz.ch funding-acknowledgement: Ministry of Education, Culture, Science, Sport and Technology, Japan; Ministry of Education, Culture, Science, Sport and Technology of Japanese Government [18104009, 22000002]; SNF grant [200020-130100/1] funding-text: We thank H. Terasaki, Y. Shibazaki, S. Ozawa, T. Sakamaki, H. Hayashi and K. Nishida for their technical help at ‘SPring-8’. We greatly appreciate the discussion and suggestions by Tomo Katsura which improved the quality of the manuscript. We thank Gyorgy Hetenyi for various discussions on geophysical aspects on the current project. We also thank two anonymous reviewers for constructive reviews. The experiments were conducted when S.G. was at Tohoku University, while most of the manuscript was written while S.G. was at ETH Zurich. S.G. gratefully acknowledges the Ministry of Education, Culture, Science, Sport and Technology, Japan for providing him the Monbukagakusho Fellowship. This work was supported by the Grants-in-aid for Scientific Research from Ministry of Education, Culture, Science, Sport and Technology of Japanese Government (Nos. 18104009 and 22000002) to E.O., and conducted as a part of the 21st Century-of-Excellence program, ‘Advanced Science and Technology Center for the Dynamic Earth’ and Global Center of Excellence program, ‘Global Education and Research Center for the Earth and Planetary Dynamics’ at Tohoku University. At ETH Zurich, S.G. was supported by a SNF grant (# 200020-130100/1) which is gratefully acknowledged. number-of-cited-references: 81 times-cited: 0 journal-iso: Earth Planet. Sci. Lett. doc-delivery-number: 173KC unique-id: ISI:000321077400011
We have determined the post-spinel transition boundary in anhydrous and hydrous Mg2SiO4 in a temperature range from 1173 to 2023 K at 19.3-25.4 GPa using synchrotron in situ X-ray diffraction measurements. The phase boundary in Mg2SiO4 is located at 22 GPa and 1800 K and 22.1 GPa and 1500 K, which is slightly lower (similar to 0.3-0.5 GPa) than that determined in the previous in situ measurements using the same pressure scale [e.g. Katsura et al., 2003, Post-spinel transition in Mg2SiO4 determined by high P-T in situ X-ray diffractometry. Phys. Earth Planet. Inter. 136, 11-24]. The Clapeyron slope of Mg2SiO4 was found to be gentle i.e. between -0.4 and -0.7 MPa/K, which is also consistent with previous in situ measurements, but inconsistent with diamond anvil cell experiments and theoretical estimations. The phase boundary in Mg2SiO4+2 wt% H2O which is relevant to Fe free-depleted harzburgitic composition is located between 23.4 and 23.6 GPa and 1500 K, which shifts the hydrous boundary to the higher pressures relative to anhydrous Mg2SiO4 from 1.3 to 1.0 GPa. The result for hydrous Mg2SiO4 shows steeper Clapeyron slope between -3.2 and -3.1 MPa/K compared with anhydrous Mg2SiO4 and hydrous pyrolite system. The present data suggest that water has a strong influence on 660 km discontinuity and the depressions observed at this boundary in several regions, especially related to subduction zones, can be explained by the presence of water in depleted harzburgite component. (c) 2013 Elsevier B.V. All rights reserved.
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