TY - JOUR
T1 - Hydrous minerals and the storage of water in the deep mantle
AU - Ohtani, Eiji
N1 - Funding Information:
The author thanks I. Ohira, I. Mashino, Y. Amaike, A. Suzuki, S. Kamada, T. Sakamaki, M. Murakami, K. D. Litasov, S. V. Rashchenko, and N. Sobolev for the useful discussions on this manuscript. This work was supported by a JSPS KAKENHI grant no. 22000002 awarded to EO and also supported partly by a grant from the Ministry of Education and Science of the Russian Federation , Project 14.B25.31.0032 , awarded to EO.
Publisher Copyright:
© 2015 Elsevier B.V.
PY - 2015/12/15
Y1 - 2015/12/15
N2 - Water is transported into the deep mantle via hydrous minerals in subducting slabs. During subduction, a series of minerals in these slabs such as serpentine or chlorite, Mg-sursassite and/or the 10 Å phase, and phase A can be stable at different pressures within the slab geotherms, and may transport significant amount of water into the Earth's interior. The transition zone has a large water storage capacity because of the high solubility of water in wadsleyite and ringwoodite. The recent discovery of hydrous ringwoodite and phase Egg as inclusions in ultra deep diamonds from Juina, Brazil suggests that the transition zone may indeed contain water. Seismic tomographic studies and electrical conductivity observations suggest that the transition zone may contain large amount of water, at least locally, beneath the subduction zones. The discovery of a new hydrous phase H, MgSiO2(OH)2, and its solid solution with isostructural phase δ-AlOOH, suggests that a significant amount of water could be stored in this hydrous magnesium silicate phase which is stable down to the lower mantle. Water may be transported into the bottom of the lower mantle via phase H-δ solid solution in descending slabs. This new high pressure hydrous phase solid solution has a high bulk modulus and sound velocity owing to strong O-H bonding due to hydrogen bond symmetrization in the lower mantle. Therefore, water stored in this hydrous phase would not reduce the seismic wave velocity in the lower mantle, and is seismically invisible. Dehydration melting could then occur at the base of the lower mantle, providing a potential explanation for the ultralow-velocity zone at the core-mantle boundary. When this hydrous magnesium silicate phase or hydrous melt makes contact with the metallic outer core at the core-mantle boundary, then hydrogen is likely to dissolve into the core.
AB - Water is transported into the deep mantle via hydrous minerals in subducting slabs. During subduction, a series of minerals in these slabs such as serpentine or chlorite, Mg-sursassite and/or the 10 Å phase, and phase A can be stable at different pressures within the slab geotherms, and may transport significant amount of water into the Earth's interior. The transition zone has a large water storage capacity because of the high solubility of water in wadsleyite and ringwoodite. The recent discovery of hydrous ringwoodite and phase Egg as inclusions in ultra deep diamonds from Juina, Brazil suggests that the transition zone may indeed contain water. Seismic tomographic studies and electrical conductivity observations suggest that the transition zone may contain large amount of water, at least locally, beneath the subduction zones. The discovery of a new hydrous phase H, MgSiO2(OH)2, and its solid solution with isostructural phase δ-AlOOH, suggests that a significant amount of water could be stored in this hydrous magnesium silicate phase which is stable down to the lower mantle. Water may be transported into the bottom of the lower mantle via phase H-δ solid solution in descending slabs. This new high pressure hydrous phase solid solution has a high bulk modulus and sound velocity owing to strong O-H bonding due to hydrogen bond symmetrization in the lower mantle. Therefore, water stored in this hydrous phase would not reduce the seismic wave velocity in the lower mantle, and is seismically invisible. Dehydration melting could then occur at the base of the lower mantle, providing a potential explanation for the ultralow-velocity zone at the core-mantle boundary. When this hydrous magnesium silicate phase or hydrous melt makes contact with the metallic outer core at the core-mantle boundary, then hydrogen is likely to dissolve into the core.
KW - Hydrogen bond symmetrization
KW - Hydrous mineral
KW - Hydrous phase H
KW - Hydrous phase δ
KW - Slab
KW - Water
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U2 - 10.1016/j.chemgeo.2015.05.005
DO - 10.1016/j.chemgeo.2015.05.005
M3 - Article
AN - SCOPUS:84958633860
VL - 418
SP - 6
EP - 15
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
ER -