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| Titel |
Linking the dynamics and evolution of lower mantle heterogeneities with surface plate motion history |
| VerfasserIn |
Abigail Bull, Christine Thomas |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106280
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| Publikation (Nr.) |
 EGU/EGU2015-11593.pdf |
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| Zusammenfassung |
| Numerical studies of mantle convection have attempted to explain tomographic observations that
reveal a lower mantle dominated by broad regional areas of lower-than-average shear-wave
speeds beneath Africa and the Central Pacific. Termed LLSVPs (“large low shear velocity
provinces”), the anomalous regions are often inferred to be thermochemical structures encircled
by regions of higher-than-average shear-wave speeds associated with Mesozoic and Cenozoic
subduction zones. Geochemical inferences of multiple chemical reservoirs at depth, strong
seismic contrasts, an anti-correlation of shear-wave velocity to bulk sound velocity and increased
density in the anomalous regions support a thermochemical origin for the LLSVPs. The origin and
long-term evolution of the anomalous regions remains enigmatic. It has been proposed that the
LLSVP beneath Africa was not present before 200 Ma (i.e. before and during most of the life-time
of the supercontinent Pangea), prior to which time the lower mantle was dominated by a degree-1
convection pattern with a major upwelling centred close to the present-day Pacific LLSVP and
subduction concentrated mainly in the antipodal hemisphere. The African LLSVP would thus have
formed during the time-frame of the supercontinent Pangea as a result of return flow in the mantle
due to circum-Pacific subduction. We present new results from a geodynamic-seismology study
that investigates the hypothesis that the Pacific LLSVP is indeed much older than its antipodal
counterpart by performing 3D numerical models of mantle convection integrated with a new plate
tectonic history model. We improve upon previous studies by imposing kinematic surface
velocity boundary conditions for a time interval that spans the amalgamation and subsequent
break-up of Pangea and by allowing for a lateral heterogeneity difference between the African and
the Pacific LLSVPs. Our results are distinct from those of previous studies in several important
ways: our plate model explicitly includes (i) absolute longitudinal reconstructions and (ii) TPW correction,
(iii) our model extends back to the mid-Paleozoic (410 Ma) and (iii) we include lateral
compositional variations between the two antipodal LLSVPs. |
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