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Seismic evidence that the source of the Iceland hotspot lies at the core–mantle boundary

Nature volume 396, pages 251–255 (1998)Cite this article

Abstract

Although Morgan1 proposed in 1971 that hotspots such as Iceland were the result of hot, rising mantle plumes, it is still debated whether plumes originate from a thermal boundary just above the core–mantle boundary or at the base of the upper mantle2. Although seismic evidence of plumes in the upper mantle is accumulating3, narrow plume conduits in the deep mantle have yet to be detected. Details of plume formation in the lower mantle have therefore remained largely unconstrained4. Here, however, we present seismic evidence for the presence of a localized patch of material with ultra-low seismic wave speed, located at the core–mantle boundary beneath the Iceland hotspot, and propose that this zone represents the hot, partially molten source region of the Iceland mantle plume. Through the modelling of seismic waveforms, we constrain the seismic velocity structure at this patch of the core–mantle boundary using a numerical–analytical interfacing code5 designed to reproduce the complex interference of shear-wave phases transmitted through, and refracted at, the boundary6. Although this structure is difficult to constrain precisely, our preferred model consists ofadome which is 250 km wide, 40 km high and contains P- and S-wave velocity (wave-speed) reductions of 10% and 30%, respectively.

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Figure 1: Ray-path geometry.
Figure 2: Sampling of the core–mantle boundary and corresponding record section.
Figure 3: Observations of South American events recorded in Europe divided into two groups, normal and anomalous, along with three sets of synthetics.
Figure 4: Magnified view of the region beneath the North Atlantic indicating the core-exit points of SKS (crosses) and SKKS (squares).

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Acknowledgements

We thank J. Ritsema for comments on early drafts. This work was supported by the NSF.

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  1. Seismological Laboratory 252-21, California Institute of Technology, Pasadena, 91125, California, USA

    D. V. Helmberger, L. Wen & X. Ding

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  1. D. V. Helmberger
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  2. L. Wen
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  3. X. Ding
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Correspondence to D. V. Helmberger.

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Helmberger, D., Wen, L. & Ding, X. Seismic evidence that the source of the Iceland hotspot lies at the core–mantle boundary. Nature 396, 251–255 (1998). https://doi.org/10.1038/24357

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