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Bent-shaped plumes and horizontal channel flow beneath the 660 km discontinuity

Tosi, Nicola and Yuen, D. A. (2011) Bent-shaped plumes and horizontal channel flow beneath the 660 km discontinuity. Earth and Planetary Science Letters, 312, pp. 348-359. Elsevier. doi: doi:10.1016/j.epsl.2011.10.015.

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Official URL: http://www.sciencedirect.com/science/article/pii/S0012821X1100608X


Recent high-resolution seismic imaging of the transition zone topography beneath the Hawaiian archipelago shows strong evidence for a 1000 to 2000 km wide hot thermal anomaly ponding beneath the 660 km boundary west of Hawaii islands [Q. Cao et al. Seismic imaging of transition zone discontinuities suggests hot mantle west of Hawaii. Science (2011), 332, 1068–1071]. This scenario suggests that Hawaiian volcanism may not be caused by a stationary narrow plume rising from the core–mantle boundary but by hot plume material first held back beneath the 660 km discontinuity and then entrained under the transition zone before coming up to the surface. Using a cylindrical model of iso-chemical mantle convection with multiple phase transitions, we investigate the dynamical conditions for obtaining this peculiar plume morphology. Focusing on the role exerted by pressure-dependent thermodynamic and transport parameters, we show that a strong reduction of the coefficient of thermal expansion in the lower mantle and a viscosity hill at a depth of around 1800 km allow plumes to have enough focused buoyancy to reach and pass the 660 km depth interface. The lateral spreading of plumes near the top of the lower mantle manifests itself as a channel flow whose length is controlled by the viscosity contrast due to temperature variations ∆ηT. For small values of ∆ηT, broad and highly viscous plumes are generated that tend to pass through the transition zone relatively unperturbed. For higher values (10^2 ≤ ∆ηT ≤ 10^3), we obtain horizontal channel flows beneath the 660 km boundary as long as 1500 km within a timescale that resembles that of Hawaiian hotspot activity. This finding could help to explain the origin of the broad hot anomaly observed west of Hawaii. For a normal thermal anomaly of 450 K associated with a lower mantle plume, we obtain activation energies of about 400 kJ/mol and 670 kJ/mol for ∆ηT = 10^2 and 10^3, respectively, in good agreement with values based on lower mantle mineral physics. If an increase of the thermal conductivity with depth is also included, our model can predict both long channel flows beneath the 660 km discontinuity and also values of the radial velocity of local blobs sinking in the lower mantle of around 1 cm/yr, in good agreement with those inferred for the sinking rate of cold remnants of the subducted lithosphere.

Item URL in elib:https://elib.dlr.de/72886/
Document Type:Article
Title:Bent-shaped plumes and horizontal channel flow beneath the 660 km discontinuity
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Tosi, Nicolanicola.tosi (at) dlr.deUNSPECIFIED
Yuen, D. A.University of Minnesota, Minneapolis, USAUNSPECIFIED
Journal or Publication Title:Earth and Planetary Science Letters
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:Yes
DOI :doi:10.1016/j.epsl.2011.10.015
Page Range:pp. 348-359
Keywords:mantle plumes; phase transitions; temperature dependent viscosity; thermal expansivity; lattice thermal conductivity
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EW - Erforschung des Weltraums
DLR - Research area:Space
DLR - Program:W EW - Erforschung des Weltraums
DLR - Research theme (Project):W - Vorhaben Exploration des Sonnensystems (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Physics
Institute of Planetary Research
Deposited By: Noack, Lena
Deposited On:16 Dec 2011 14:23
Last Modified:10 Jan 2019 15:47

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