Abstract
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS,
VOL. 10,
Q05W03,
18 PP., 2009
doi:10.1029/2009GC002401 [Citation]
Tomographic filtering of high-resolution mantle circulation models: Can seismic heterogeneity be explained by temperature alone?
Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Theresienstrasse 41, D-80333, Munich, Germany
Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Theresienstrasse 41, D-80333, Munich, Germany
Department of Geological Sciences, University of Michigan, 2534 C. C. Little Building, 1100 North University Avenue, Ann Arbor, Michigan 48109, USA
High-resolution mantle circulation models (MCMs) together with thermodynamic mineralogical models make it possible to construct
3-D elastic mantle heterogeneity based on geodynamic considerations. Recently, we have shown that in the presence of a strong
thermal gradient across D″ and corresponding large temperature variations in the lower mantle, the heterogeneity predicted
from isochemical whole mantle flow agrees well with tomographic models in terms of magnitudes of S wave velocity (v s ) variations. Here, we extend the comparison of geodynamic and tomographic structures by accounting explicitly for the limited
resolving power of tomography. We focus on lateral variations in v s and use the resolution operator
associated with S20RTS to modify our geodynamic models so that they reflect the long-wavelength (>1000 km) nature and the
effects of heterogeneous data coverage and damping inherent to the tomographic inversion. Prior to the multiplication with
, the geodynamic models need to be reparameterized onto the basis of S20RTS. The magnitude reduction introduced by this reparameterization
is significant and needs careful assessment. We attempt a correction of the reparameterization effects and find that the inherent
tomographic filtering alone then leads to a magnitude reduction by a factor of ∼2 in the lower mantle. Our tomographically
filtered models with strong core heating agree well with S20RTS, which resolves maximum negative anomalies of around −1.5%
in the lowermost mantle. Temperature variations on the order of +1000 K, corresponding to perturbations of around −3% in v s in the unfiltered model, would be seen as −1.5% when “imaged” with the data and damping of S20RTS. This supports our earlier
finding that isochemical whole mantle flow with strong core heating and a pyrolite composition can be reconciled with tomography.
In particular, the large lateral temperature variations associated with lower mantle plumes are able to account for the slow
seismic anomalies in the large low-velocity zones under Africa and the Pacific. We also find that strong gradients in shear
wave velocity of 2.25% per 50 km in our unfiltered models compare well with the sharp sides of the African superplume.
Received 26 January 2009; accepted 27 March 2009; published 20 May 2009.
Citation: (2009), Tomographic filtering of high-resolution mantle circulation models: Can seismic heterogeneity be explained by temperature alone?, Geochem. Geophys. Geosyst., 10, Q05W03, doi:10.1029/2009GC002401.
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