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| Titel |
The Importance of Asthenospheric Temperature Anomalies in Maintaining Observed Dynamic Topography |
| VerfasserIn |
Fred Richards, Mark Hoggard, Nicky White |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250154048
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| Publikation (Nr.) |
 EGU/EGU2017-19094.pdf |
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| Zusammenfassung |
| A new compilation of observed oceanic residual depth anomalies show that ∼±1 km of
dynamic topography occurs at wavelengths of 103–104 km. At the same time, seismic studies
provide strong evidence for the existence of a substantial and widespread low-viscosity
channel beneath the oceanic basins. In light of these observations, we investigate whether the
shorter wavelength (< 4,000 km) signal in the global residual depth database can be
linked to temperature variations within this sub-plate channel. We calculate upper
mantle temperature structure using an experimentally-derived anelasticity model
that is calibrated against shear wave velocity and attenuation constraints. Residual
depth anomalies are predicted for a range of channel thicknesses and tomographic
models by converting upper mantle temperature anomalies to density anomalies
and calculating the isostatic response. We find that thermal anomalies of ±150 ∘C
within a 100–175 km thick channel yield a better match to residual depth anomalies
than many predictive geodynamic models. Oceanic viscosity profiles calculated
using the above parameterisation suggest that the average viscosity is two orders of
magnitude lower within the channel than in the underlying upper mantle, confirming the
validity of an isostatic calculation at shorter wavelengths. Spectral cross-correlation
shows that an isostatic approximation yields poorer results at wavelengths > 7,000
km, consistent with sensitivity kernel considerations. These results suggest that
observed dynamic topography in the oceanic realm can be primarily attributed to
temperature-induced buoyancy variations within an asthenospheric channel with more
minor contributions from the deeper mantle. Our work indicates that incorporation
of better resolved surface wave tomography of the upper mantle combined with
an improved treatment of the lithosphere-asthenosphere system in geodynamic
models may hold the key to reconciling observed and predicted dynamic topography. |
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