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TitleAnisotropic structure of the central North American Craton surrounding the Mid-Continent Rift: evidence from Rayleigh waves
AuthorFoster, A; Darbyshire, F; Schaeffer, AORCID logo
SourcePrecambrian Research vol. 342, 20190346, 2020 p. 1-18,
Alt SeriesNatural Resources Canada, Contribution Series 20190346
Mediapaper; on-line; digital
File formatpdf; html
ProvinceOntario; Quebec; Manitoba; Nunavut; Saskatchewan; Northwest Territories
NTS21; 22; 23; 24; 25; 30; 31; 32; 33; 34; 35; 40; 41; 42; 43; 44; 45; 52; 53; 54; 55; 62; 63; 64; 65; 72; 73; 74; 75
AreaGreat Lakes; Hudson Bay; Canada; United States of America
Lat/Long WENS-105.0000 -70.0000 64.0000 38.0000
Subjectsstructural geology; tectonics; geophysics; Science and Technology; Nature and Environment; crustal structure; lithosphere; craton; mantle; tectonic setting; tectonic evolution; rifting; orogenesis; magmatism; seismic interpretations; seismic waves; r waves; s waves; anisotropy; seismic velocities; seismological network; models; Archean; North American Craton; Mid-Continent Rift; Trans-Hudson Orogen; Superior Craton; Grenville Orogen; Laurentia; Canadian Shield; Nipigon Embayment; Matachewan Dyke Swarm; Great Meteor Hot Spot; Precambrian; Proterozoic
Illustrationsgeoscientific sketch maps; tables; profiles
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2020 02 22
AbstractThe subsurface of the central North American Craton has been imaged by body-, surface-, and full-waveform studies at varying resolutions. These studies offer tantalizing clues about the evolution of Archean and Proterozoic lithosphere. The oldest cratonic lithosphere may have been formed under a different or pre-plate-tectonic regime and, in this region, was later modified by orogenesis around the edges, hotspot passage, rifting and magmatism. We improve the resolution of seismic imaging across the Great Lakes region of North America by carrying out two-station phase velocity dispersion measurements at selected station pairs and inverting them for anisotropic phase velocity maps at periods 20-200 s. We also perform extensive resolution tests to identify robust features in the data. Isotropic features to note are the strong signatures of the Trans-Hudson Orogen, Superior Craton, and Mid-Continent Rift (MCR) at periods most sensitive to the lower crust and uppermost mantle, relatively low velocities near the Great Lakes region at periods most sensitive to the middle lithosphere, and extremely fast velocities in the western Superior at long periods, corresponding to the lowermost cratonic lithosphere. We note a strong contrast in seismic anisotropy across the MCR, with strong anisotropy to the north and weaker anisotropy to the south at shorter periods, consistent with observations from other data types and studies. Fast orientations are heterogeneous within the Superior craton at intermediate periods. At periods greater than or equal to 160 s, an increase in magnitude of the anisotropy, and coherence of the fast orientation, suggest an asthenospheric contribution to the signal.
Summary(Plain Language Summary, not published)
The stable, central cores of continental interiors, called cratons, have typically been interpreted to be solid, long-lasting bastions which remain unaltered over billions of years. However, over recent decades, we have learned that in many cases, this is not always the case. These cratonic cores can in fact be altered, and their very alteration can have significant impacts for 100s of millions of years. In this study, we examine the long-lived alternation of the central North American craton, through the Great Lakes region, which is the home of the failed mid-continental rift system. This rifting episode, which occurred roughly 1.1 billion years ago, has left lasting scars on the crust and lithosphere. These scars can potentially impact the subsequent location of intraplate seismicity, as a result of alteration and fabrics that are created in the rocks.

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