Strong, multi-scale heterogeneity in earth's lowermost mantle

© 2015 IOP Publishing Ltd. Calculations were performed on the Terrawulf cluster, a computational facility supported through the AuScope Australian Geophysical Observing System (AGOS). AuScope is funded under the National Collaborative Research Infrastructure Strategy (NCRIS), and the Education investment Fund (EIF3) both Australian Commonwealth Government Programs. D. R. D. is funded by an ARC Future Fellowship (FT140101262). M. M. acknowledges financial support by the Spanish Ministry of Economy and Competitiveness (CGL 2013-41860-P) and by the BBVA Foundation (PR14 CMA10). We are thankful to J. Byrne for his assistance with Terrawulf cluster and M. Sambridge and T. Bodin for useful discussions regarding technical aspects of the Bayesian inversion. All figures were made by The Generic Mapping Tools.
The core mantle boundary (CMB) separates Earth's liquid iron outer core from the solid but slowly convecting mantle. The detailed structure and dynamics of the mantle within similar to 300 km of this interface remain enigmatic: it is a complex region, which exhibits thermal, compositional and phase-related heterogeneity, isolated pockets of partial melt and strong variations in seismic velocity and anisotropy. Nonetheless, characterising the structure of this region is crucial to a better understanding of the mantle's thermo-chemical evolution and the nature of core-mantle interactions. In this study, we examine the heterogeneity spectrum from a recent P-wave tomographic model, which is based upon trans-dimensional and hierarchical Bayesian imaging. Our tomographic technique avoids explicit model parameterization, smoothing and damping. Spectral analyses reveal a multi-scale wavelength content and a power of heterogeneity that is three times larger than previous estimates. Inter alia, the resulting heterogeneity spectrum gives a more complete picture of the lowermost mantle and provides a bridge between the long-wavelength features obtained in global S-wave models and the short-scale dimensions of seismic scatterers. The evidence that we present for strong, multi-scale lowermost mantle heterogeneity has important implications for the nature of lower mantle dynamics and prescribes complex boundary conditions for Earth's geodynamo.
National Collaborative Research Infrastructure Strategy (NCRIS), Australia
Education investment Fund (EIF3), Australia
Ministerio de Economía y Competitividad (MINECO), España
Fundación BBVA
Australian Commonwealth Government Program
Future Fellowship, Australian Research Council (ARC)
Depto. de Física de la Tierra y Astrofísica
Fac. de Ciencias Físicas
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