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Two-stage subduction history under North America inferred from multiple-frequency tomography

Sigloch, Karin, Nadine McQuarrie, and Guust Nolet (2008), Two-stage subduction history under North America inferred from multiple-frequency tomography, Nature Geoscience, doi:10.1038/ngeo231.

Eastward subduction of oceanic tectonic plates has shaped the geologic history of western North America over the past 150 million years1,2,3,4. The mountain-building and volcanism that brought forth the spectacular landscapes of the West are credited to the vast ancient Farallon plate, which interacted mechanically and chemically with the overlying continent as it plunged back into the mantle. Here we use finite-frequency traveltime and amplitude measurements of teleseismic P-waves in seven frequency bands to obtain a high-resolution tomographic image to ~1800 km depth. We discover several large, previously unknown pieces of the plate which show that two distinct stages of whole-mantle subduction are present under North America. The currently active one descends from the Pacific Northwest coast to 1500 km depth beneath the Great Plains, whereas its stalled predecessor occupies the transition zone and lower mantle beneath the eastern half of the continent. We argue that the separation between them is linked to the Laramide era 70-50 Myr ago, a time of unusual volcanism and mountain building far inland generally explained by an episode of extremely flat subduction.

Complementary pieces of the Farallon plate have been illuminated by different seismic methods. Near the trench of its currently descending small remnant, the Juan de Fuca plate (figure 1), it has been imaged down to ~400 km depth by regional array studies6,7,8,9. Surface-wave studies10 observed extended high-velocity zones in the transition zone under western North America. In the lower mantle beneath the continent’s east coast, global-scale body-wave tomography picked up on a robust band of fast Farallon material11,12. However, its connection to the shallower western pieces was ambiguous, since large volumes beneath the central and eastern U.S. remained unresolved. This gap is filled by the present study. Surprisingly, the newly discovered fragments in transition zone and lower mantle do not follow the norm that deeper material is always older. We also resolve tears or fractures in the submerged plate that are thousands of kilometers long. These detailed new observations on the plate’s current geometry call for a critical review of earlier ideas about its subduction history.

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  • 2008_SiglochMcQuarrieNolet_SupplFigures5.pdf
  • BibTeX
      author = {Karin Sigloch and Nadine McQuarrie and Guust Nolet},
      journal = {Nature Geoscience},
      month = {jun},
      title = {{Two-stage subduction history under North America inferred from multiple-frequency tomography}},
      year = {2008},
      url = {http://www.geophysik.uni-muenchen.de/~sigloch/papers/2008{\_}SiglochMcquarrieNolet{\_}NatGeo.pdf},
      doi = {10.1038/ngeo231},
    %0 Journal Article
    %A Sigloch, Karin
    %A McQuarrie, Nadine
    %A Nolet, Guust
    %D 2008
    %J Nature Geoscience
    %T Two-stage subduction history under North America inferred from multiple-frequency tomography
    %U http://www.geophysik.uni-muenchen.de/~sigloch/papers/2008_SiglochMcquarrieNolet_NatGeo.pdf
    %U http://www.geophysik.uni-muenchen.de/~sigloch/papers/2008_SiglochMcQuarrieNolet_SupplFigures1234.pdf
    %U http://www.geophysik.uni-muenchen.de/~sigloch/papers/2008_SiglochMcQuarrieNolet_SupplFigures5.pdf
    %8 jun
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    Printed 22. Sep 2020 06:51