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| Titel |
Effects of low post-perovskite viscosity on thermal-chemical-phase structures and heat flow across the CMB |
| VerfasserIn |
T. Nakagawa, P. Tackley |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250025646
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| Zusammenfassung |
| Recent first principle calculations make it possible to infer rheological properties such as
activation energy and volume in deep mantle phases, including perovskite [Ammann et al.,
2008] and post-perovskite, which is expected to have a much lower viscosity than perovskite
[J. Brodholt, personal communication] as well as other mineral phases with different
rheological properties [e.g. Yamazaki and Karato, 2001]. The expected low viscosity of
post-perovskite should have strong dynamical effects, which would influence structures in the
CMB region. Thus, we here we expand our numerical models of thermo-chemical mantle
convection with post-perovskite [Nakagawa and Tackley, 2008, 2006, 2005; Tackley et
al, 2007] to include different rheological parameters for different mantle phases.
The dynamical effects are investigated using simulations in a two-dimensional
spherical annulus [Hernlund and Tackley, 2008] and/or a full 3-D spherical shell
[Tackley, 2008] with different viscosity prefactors for the post-perovskite phase and
including a composition-dependent post-perovskite phase transition. We focus on
how seismic structures generated by combined thermal, compositional and phase
change effects are influenced by the low viscosity of post-perovskite. In addition to
studying spatial Vs structures, we also calculate diagnostics such as the spectrum
of seismic wave anomalies, and compare results to seismic observations [Lay et
al., 2006; van der Hilst et al., 2007], in order to determine whether the mineral
physics findings and seismic images can be reconciled using a consistent dynamical
calculation. Furthermore, we test the theory of [Buffett, 2007] regarding the influence of
the post-perovskite transition on heat flux through the CMB. Finally, we calculate
histograms of model seismic wave anomalies, which have recently been used to
make inferences about compositional anomalies in the deep mantle, [Hernlund and
Houser, 2008] to determine how well these statistical diagnostics actually give
information about the structures that cause them. Detailed findings will be provided in the
presentation.
References
Ammann, M.W., Brodholt, J.P. and Dobson, D.P., 2008. DFT study of migration
enthalpies in MgSiO3 perovskite. Phys. Chem. Minerals: doi: 10.1007/s00269-008-0265-z.
Hernlund and Houser (2008)
Nakagawa, T., and P. J. Tackley (2008) Lateral variations in CMB heat flux and deep
mantle seismic velocity caused by a thermal-chemical-phase boundary layer in 3D spherical
convection, Earth Planet. Sci. Lett. 271, 348-358.
Nakagawa, T., and P. J. Tackley (2007) The interaction between the post-perovskite phase
change and a thermo-chemical boundary layer near the core-mantle boundary, Earth Planet.
Sci. Lett., 238, 204-216.
Nakagawa, T., and P. J. Tackley (2006) Three-dimensional structures and dynamics in the
deep mantle: Effects of post-perovskite phase change and deep mantle layering, Geophys.
Res. Lett., 33 L12S11, doi:1029/2006GL025719.
Tackley, P. J., T. Nakagawa and J. W. Hernlund, Influence of the post-perovskite transition
on thermal and thermo-chemical mantle convection, in AGU Geophysical Monograph
on "The Last Phase Transition", ed. K. Hirose, J. Brodholt, T. Lay, D. A. Yuen. |
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