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Mantle discontinuities and temperature under the North American continental keel

Nature volume 395, pages 160–163 (1998)Cite this article

Abstract

A ubiquitous feature of upper-mantle seismic velocity models has been the presence of high-velocity ‘keels’ beneath stable continental interiors1,2,3,4,5. Uncertainty remains, however, regarding the maximum depth to which continental keels extend, the degree to which they have cooled the mantle that surrounds them and their role in mantle flow. Here we investigate thermal anomalies across the eastern margin of the North American continental keel by imaging the seismic discontinuities at depths of 410 and 660 km with compressional-to-shear converted waves recorded by a 1,500-km-long seismometer deployment in the eastern United States. The thickness of the transition zone (the region nominally between depths of 410 and 660 km) and the depth to the ‘410-km’ discontinuity indicate that cold keel material and sub-keel downwellings must be largely confined to the upper mantle and may impinge on the transition zone only in localized regions and with thermal anomalies of less than ∼150 K. A 20-km depression of the ‘660-km’ discontinuity to the south of the westernmost stations coincides with a region of fast velocity in the deep transition zone2 and may be associated with the remnants of the subducted Farallon plate1,2,4.

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Figure 1: Ps conversion points at depths of 410 km (small black symbols) and 660 km (small white symbols) plotted on S-wave velocity anomalies from Grand2 for depths of 175–250 km.
Figure 2: Ps receiver function stacks from bins to the north (a) and to the south (b) of the MOMA array.
Figure 3: Discontinuity topography, transition zone (TZ) thickness, and deep transition-zone velocity anomalies beneath the MOMA array.

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Acknowledgements

We thank S. van der Lee and S. Grand for their mantle velocity models, Y. Shen for assistance with the receiver function analysis, G. Helffrich for a review, the IRIS/PASSCAL program for the seismometers used in the MOMA experiment, and M. Fouch, G. Al-Eqabi, P. Shore and the Lamont PASSCAL Instrument Center for their help with the deployment. Data for stations HRV and CCM were obtained from the IRIS Data Management Center. This work was supported by the Geophysics Program of the US NSF.

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Authors and Affiliations

  1. Department of Geological Sciences, Brown University, Providence, 02912, Rhode Island, USA

    Aibing Li & Karen M. Fischer

  2. Department of Earth and Planetary Sciences, Washington University, St Louis, 63130, Missouri, USA

    Michael E. Wysession

  3. Department of Earth and Environmental Sciences, New Mexico Institute of Mining and Technology, Socorro, 87801, New Mexico, USA

    Timothy J. Clarke

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Correspondence to Aibing Li.

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Li, A., Fischer, K., Wysession, M. et al. Mantle discontinuities and temperature under the North American continental keel. Nature 395, 160–163 (1998). https://doi.org/10.1038/25972

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