TY - JOUR
T1 - Effect of water in depleted mantle on post-spinel transition and implication for 660km seismic discontinuity
AU - Ghosh, Sujoy
AU - Ohtani, Eiji
AU - Litasov, Konstantin D.
AU - Suzuki, Akio
AU - Dobson, David
AU - Funakoshi, Kenichi
N1 - Funding Information:
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 György Hetényi 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.
PY - 2013/6
Y1 - 2013/6
N2 - We have determined the post-spinel transition boundary in anhydrous and hydrous Mg2SiO4 in a temperature range from 1173 to 2023K at 19.3-25.4GPa using synchrotron in situ X-ray diffraction measurements. The phase boundary in Mg2SiO4 is located at 22GPa and 1800K and 22.1GPa and 1500K, which is slightly lower (~0.3-0.5GPa) 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 -0.7MPa/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+2wt% H2O which is relevant to Fe free-depleted harzburgitic composition is located between 23.4 and 23.6GPa and 1500K, which shifts the hydrous boundary to the higher pressures relative to anhydrous Mg2SiO4 from 1.3 to 1.0GPa. The result for hydrous Mg2SiO4 shows steeper Clapeyron slope between -3.2 and -3.1MPa/K compared with anhydrous Mg2SiO4 and hydrous pyrolite system. The present data suggest that water has a strong influence on 660km 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.
AB - We have determined the post-spinel transition boundary in anhydrous and hydrous Mg2SiO4 in a temperature range from 1173 to 2023K at 19.3-25.4GPa using synchrotron in situ X-ray diffraction measurements. The phase boundary in Mg2SiO4 is located at 22GPa and 1800K and 22.1GPa and 1500K, which is slightly lower (~0.3-0.5GPa) 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 -0.7MPa/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+2wt% H2O which is relevant to Fe free-depleted harzburgitic composition is located between 23.4 and 23.6GPa and 1500K, which shifts the hydrous boundary to the higher pressures relative to anhydrous Mg2SiO4 from 1.3 to 1.0GPa. The result for hydrous Mg2SiO4 shows steeper Clapeyron slope between -3.2 and -3.1MPa/K compared with anhydrous Mg2SiO4 and hydrous pyrolite system. The present data suggest that water has a strong influence on 660km 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.
KW - 660km discontinuity
KW - Mg-perovskite
KW - Post-spinel transition
KW - Ringwoodite
KW - Transition zone
KW - Water
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U2 - 10.1016/j.epsl.2013.04.011
DO - 10.1016/j.epsl.2013.04.011
M3 - Article
AN - SCOPUS:84878474922
SN - 0012-821X
VL - 371-372
SP - 103
EP - 111
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
ER -