Lithospheric expression of geological units in central and eastern North America from full waveform tomography

Y. Huaiyu and S. French and Paul Cupillard and B. Romanowicz. ( 2014 )
in: Earth Planet. Sci. Lett., 402 (176–186)

Abstract

The EarthScope TA deployment has provided dense array coverage throughout the continental US and with it, the opportunity for high resolution 3D seismic velocity imaging of both lithosphere and asthenosphere in the continent. Building upon our previous long-period waveform tomographic modeling in North America, we present a higher resolution 3D isotropic and radially anisotropic shear wave velocity model of the North American lithospheric mantle, constructed tomographically using the spectral element method for wavefield computations and waveform data down to 40 s period. The new model exhibits pronounced spatial correlation between lateral variations in seismic velocity and anisotropy and major tectonic units as defined from surface geology. In the center of the continent, the North American craton exhibits uniformly thick lithosphere down to 200–250 km, while major tectonic sutures of Proterozoic age visible in the surface geology extend down to 100–150 km as relatively narrow zones of distinct radial anisotropy, with Vsv>VshVsv>Vsh. Notably, the upper mantle low velocity zone is present everywhere under the craton between 200 and 300 km depth. East of the continental rift margin, the lithosphere is broken up into a series of large, somewhat thinner (150 km) high velocity blocks, which extend laterally 200–300 km offshore into the Atlantic Ocean. Between the craton and these deep-rooted blocks, we find a prominent narrow band of low velocities that roughly follows the southern and eastern Laurentia rift margin and extends into New England. We suggest that the lithosphere along this band of low velocities may be thinned due to the combined effects of repeated rifting processes and northward extension of the hotspot related Bermuda low-velocity channel across the New England region. We propose that the deep rooted high velocity blocks east of the Laurentia margin represent the Proterozoic Gondwanian terranes of pan-African affinity, which were captured during the Rodinia formation but left behind after the opening of the Atlantic Ocean. Our results suggest that recurring episodes of tectonic events that are well exposed at the surface also leave persistent scars in the continental lithosphere mantle, marked by isotropic and radially anisotropic velocity anomalies that reach as deep as 100–150 km.

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BibTeX Reference

@ARTICLE{,
    author = { Huaiyu, Y. and French, S. and Cupillard, Paul and Romanowicz, B. },
     title = { Lithospheric expression of geological units in central and eastern North America from full waveform tomography },
   journal = { Earth Planet. Sci. Lett. },
    volume = { 402 },
      year = { 2014 },
     pages = { 176–186 },
       doi = { 10.1016/j.epsl.2013.11.057 },
  abstract = { The EarthScope TA deployment has provided dense array coverage throughout the continental US and with it, the opportunity for high resolution 3D seismic velocity imaging of both lithosphere and asthenosphere in the continent. Building upon our previous long-period waveform tomographic modeling in North America, we present a higher resolution 3D isotropic and radially anisotropic shear wave velocity model of the North American lithospheric mantle, constructed tomographically using the spectral element method for wavefield computations and waveform data down to 40 s period. The new model exhibits pronounced spatial correlation between lateral variations in seismic velocity and anisotropy and major tectonic units as defined from surface geology. In the center of the continent, the North American craton exhibits uniformly thick lithosphere down to 200–250 km, while major tectonic sutures of Proterozoic age visible in the surface geology extend down to 100–150 km as relatively narrow zones of distinct radial anisotropy, with Vsv>VshVsv>Vsh. Notably, the upper mantle low velocity zone is present everywhere under the craton between 200 and 300 km depth. East of the continental rift margin, the lithosphere is broken up into a series of large, somewhat thinner (150 km) high velocity blocks, which extend laterally 200–300 km offshore into the Atlantic Ocean. Between the craton and these deep-rooted blocks, we find a prominent narrow band of low velocities that roughly follows the southern and eastern Laurentia rift margin and extends into New England. We suggest that the lithosphere along this band of low velocities may be thinned due to the combined effects of repeated rifting processes and northward extension of the hotspot related Bermuda low-velocity channel across the New England region. We propose that the deep rooted high velocity blocks east of the Laurentia margin represent the Proterozoic Gondwanian terranes of pan-African affinity, which were captured during the Rodinia formation but left behind after the opening of the Atlantic Ocean. Our results suggest that recurring episodes of tectonic events that are well exposed at the surface also leave persistent scars in the continental lithosphere mantle, marked by isotropic and radially anisotropic velocity anomalies that reach as deep as 100–150 km. }
}