Lithospheric layering in the North American craton

Nature, 26 August 2010, 466, 1063–1068

Huaiyu Yuan & Barbara Romanowicz

Abstract:

How cratons—extremely stable continental areas of the Earth’s crust—formed and remained largely unchanged for more than 2,500

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million years is much debated. Recent studies of seismic-wave receiver function data have detected a structural boundary under continental cratons at depths too shallow to be consistent with the lithosphere–asthenosphere boundary, as inferred from seismic tomography and other geophysical studies. Here we show that changes in the direction of azimuthal anisotropy with depth reveal the presence of two distinct lithospheric layers throughout the stable part of the North American continent. The top layer is thick (~150 km) under the Archaean core and tapers out on the surrounding Palaeozoic borders. Its thickness variations follow those of a highly depleted layer inferred from thermo-barometric analysis of xenoliths. The lithosphere–asthenosphere boundary is relatively flat (ranging from 180 to 240 km in depth), in agreement with the presence of a thermal conductive root that subsequently formed around the depleted chemical layer. Our findings tie together seismological, geochemical and geodynamical studies of the cratonic lithosphere in North America. They also suggest that the horizon detected in receiver function studies probably corresponds to the sharp mid-lithospheric boundary rather than to the more gradual lithosphere–asthenosphere boundary.

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See related papers:

Romanowicz, B. and H. Yuan (2012) On the interpretation of SKS splitting measurements in the presence of several layers of anisotropy, Geophys. J. Int., 188, 1129-1140.

Yuan, H. B. Romanowicz, K. Fischer and D. Abt (2011) 3-D shear wave radially and azimuthally anisotropic velocity model of the north American upper mantle, Geophys. J. Int., 184, 1237-1260, doi:10.1111/j.1365-246X.2010.04901.x

Yuan, H. and B. Romanowicz (2010) Depth dependent anisotropy in the western U.S. upper mantle, Earth Planet. Sci. Lett., 300, 385-394.

Marone, F. and B. Romanowicz (2007) On the depth distribution of azimuthal anisotropy in the continental upper mantle, Nature, 447, 198-201.

Marone, F. and B. Romanowicz (2007) Non-linear crustal corrections in high-resolution waveform seismic tomography, Geophys. J. Int., 170, 460-467.

Marone, F., Y. C. Gung and B. Romanowicz (2007) Three dimensional radial anisotropic structure of the North American upper mantle from inversion of surface waveform data, Geophys. J. Int., 171, 206-222: 10.1111/j.1365-246X.2007.03465.x

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