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| Titel |
Subduction to the lower mantle – a comparison between geodynamic and tomographic models |
| VerfasserIn |
B. Steinberger, T. H. Torsvik  , T. W. Becker |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 3, no. 2 ; Nr. 3, no. 2 (2012-11-26), S.415-432 |
| Datensatznummer |
250000998
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| Publikation (Nr.) |
 copernicus.org/se-3-415-2012.pdf |
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| Zusammenfassung |
| It is generally believed that subduction of lithospheric slabs is a major
contribution to thermal heterogeneity in Earth's entire mantle and provides
a main driving force for mantle flow. Mantle structure can, on the one hand,
be inferred from plate tectonic models of subduction history and geodynamic
models of mantle flow. On the other hand, seismic tomography models provide
important information on mantle heterogeneity. Yet, the two kinds of models
are only similar on the largest (1000 s of km) scales and are quite different
in their detailed structure. Here, we provide a quantitative assessment how
good a fit can be currently achieved with a simple viscous flow geodynamic
model. The discrepancy between geodynamic and tomography models can indicate
where further model refinement could possibly yield an improved fit. Our
geodynamical model is based on 300 Myr of subduction history inferred from a
global plate reconstruction. Density anomalies are inserted into the upper
mantle beneath subduction zones, and flow and advection of these anomalies is
calculated with a spherical harmonic code for a radial viscosity structure
constrained by mineral physics and surface observations. Model viscosities
in the upper mantle beneath the lithosphere are ~1020
Pas, and viscosity increases to ~1023 Pas in the lower
mantle above D". Comparison with tomography models is assessed in terms of
correlation, both overall and as a function of depth and spherical harmonic
degree. We find that, compared to previous geodynamic and tomography models,
correlation is improved, presumably because of advances in both plate
reconstructions and mantle flow computations. However, high correlation is
still limited to lowest spherical harmonic degrees. An important ingredient
to achieve high correlation – in particular at spherical harmonic degree
two – is a basal chemical layer. Subduction shapes this layer into two
rather stable hot but chemically dense "piles", corresponding to the
Pacific and African Large Low Shear Velocity Provinces. Visual comparison
along cross sections indicates that sinking speeds in the geodynamic model
are somewhat too fast, and should be 2 ± 0.8 cm yr−1 to achieve a better
fit. |
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