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| Titel |
High plume excess temperatures in the lowermost mantle |
| VerfasserIn |
Bernhard S. A. Schuberth, Hans-Peter Bunge |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041505
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| Zusammenfassung |
| It is now widely recognised that there is a substantial heat flux through the CMB from the
core into the mantle, up to 12 TW and significantly more than what was inferred earlier from
observations of dynamic topography over mantle hotspots. A strong thermal gradient across
the CMB is likely a source of large thermal anomalies in the form of hot upwelling plumes
and correspondingly low seismic velocities in the lowermost mantle. Here we focus
on temperature as a key parameter to constrain large-scale mantle structure and
dynamics. We explore high-resolution mantle circulation models and predict their
corresponding elastic heterogeneity. Absolute temperatures of our models are converted
to seismic velocities using published thermodynamically self-consistent models
of mantle mineralogy for a pyrolite composition. A grid spacing of about 25 km
globally allows us to simulate mantle flow at earth-like convective vigor so that
modelled temperature variations are consistent with the underlying mineralogy. We
concentrate on isochemical convection and the relative importance of internal and
bottom heating in order to isolate the thermal effects on elasticity. Importantly,
models having a high temperature contrast on the order of 1000 K across the CMB
produce elastic structures that are in excellent agreement with tomography for a
number of quantitative measures: These include spectral power and histograms of
heterogeneity as well as radial profiles of root-mean-square amplitudes. High plume excess
temperatures of +1000–1500 K in the lowermost mantle are particularly important in
understanding the strong velocity reductions mapped by seismic tomography in
low-velocity bodies of the deep mantle, as they lead to significant negative anomalies of
shear wave velocity of up to -4%. We note that our results do not account for the
curious observation of seismic anti-correlation, which appears difficult to explain
in any case and will require further improvements in the ability to map seismic
heterogeneity to thermal and compositional variations. Our results underline the
need to include mineral physics information in the geodynamic interpretation of
tomographic models to obtain a better understanding of seismic images of mantle plumes. |
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