globalchange  > 气候变化与战略
DOI: 10.1016/j.epsl.2020.116626
Elasticity of hydrous ringwoodite at mantle conditions: Implication for water distribution in the lowermost mantle transition zone
Author: Wang W.; Zhang H.; Brodholt J.P.; Wu Z.
Source Publication: Earth and Planetary Science Letters
ISSN: 0012821X
Publishing Year: 2021
Volume: 554
Language: 英语
keyword in Chinese: elasticity of hydrous ringwoodite ; first-principles calculations ; mantle transition zone ; water content
Keyword: Calculations ; Geochemistry ; Hydration ; Reservoirs (water) ; Seismic prospecting ; Seismology ; Shear flow ; Structural geology ; Topography ; Velocity ; Water supply systems ; First-principles calculation ; Geochemical recycling ; Global distribution ; Mantle transition zone ; Seismic observation ; Seismic tomography ; Water concentrations ; Water distributions ; Water recycling ; elasticity ; hydrous mineral ; lower mantle ; P-T conditions ; ringwoodite ; seismic velocity ; thermodynamics ; transition zone ; water content
English Abstract: The mantle transition zone (MTZ) is potentially a geochemical water reservoir because of the high H2O solubility in its dominant minerals, wadsleyite and ringwoodite. Whether the MTZ is wet or dry fundamentally impacts our understanding of the deep-water distribution, geochemical recycling, and the pattern of mantle convection. However, the water content in the MTZ inferred from previous studies remains disputed. Seismic observations such as velocity anomalies were used to evaluate the water content in the MTZ, but the hydration effect on the velocities of MTZ minerals under appropriate pressure (P) and temperature (T) conditions is poorly constrained. Here we investigated the elastic properties and velocities of hydrous ringwoodite at high P-T conditions using first-principles calculations. Our results show that the hydration effects on elastic moduli and velocities of ringwoodite are significantly reduced by pressure but strongly enhanced by temperature. The incorporation of 1.0 wt% water into ringwoodite decreases the compressional and shear velocities of the pyrolitic mantle by −1.0% and −1.4% at the conditions of MTZ, respectively. Using results from seismic tomography and together with the topography of the 660-km discontinuity, we evaluate the global distribution of water in the lower MTZ. We find that about 80% of the MTZ can be explained by varying water content and temperature, however, the remaining 20% requires the presence of high-velocity heterogeneities such as harzburgite. Our models suggest an average water concentration of ∼0.2 wt% in the lower MTZ, with an interregional variation from 0 to 0.9 wt%. Together with our previous work, we conclude that the water concentration in the MTZ likely decreases with depth globally and the whole MTZ contains the equivalent of about one ocean mass of water. © 2020 Elsevier B.V.
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Document Type: 期刊论文
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Affiliation: Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China; Department of Earth Sciences, University College London, London, WC1E 6BT, United Kingdom; Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM, United States; Centre for Earth Evolution and Dynamics, University of Oslo, Oslo, Norway; National Geophysical Observatory at Mengcheng, University of Science and Technology of China, Hefei, China; CAS Center for Excellence in Comparative Planetology, USTC, Hefei, Anhui 230026, China

Recommended Citation:
Wang W.,Zhang H.,Brodholt J.P.,et al. Elasticity of hydrous ringwoodite at mantle conditions: Implication for water distribution in the lowermost mantle transition zone[J]. Earth and Planetary Science Letters,2021-01-01,554
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