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TitleThe upper mantle structure of northwestern Canada from teleseismic body wave tomography
AuthorEstève, C; Audet, P; Schaeffer, A JORCID logo; Schutt, D; Aster, R C; Cubley, J
SourceJournal of Geophysical Research, Solid Earth vol. 125, issue 2, e2019JB018837, 2020 p. 1-18,
Alt SeriesNatural Resources Canada, Contribution Series 20190348
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf; html
ProvinceYukon; Northwest Territories; British Columbia; Alberta; Nunavut; Saskatchewan
NTS65D; 65E; 65L; 65M; 66D; 66E; 66L; 66M; 67B; 67C; 67F; 67G; 74I; 74J; 74K; 74L; 74M; 74N; 74O; 74P; 75; 76; 77; 84I; 84J; 84K; 84L; 84M; 84N; 84O; 84P; 85; 86; 87; 94I; 94J; 94K; 94L; 94M; 94N; 94O; 94P; 95; 96; 97; 104I; 104J; 104K; 104L; 104M; 104N; 104O; 104P; 105; 106; 107; 114; 115; 116; 117
AreaRocky Mountains; Mackenzie Mountains; Alaska; Canada; United States of America
Lat/Long WENS-147.0000 -103.0000 72.0000 58.0000
Subjectstectonics; geophysics; geochemistry; Science and Technology; Nature and Environment; crustal structure; mantle; lithosphere; craton; terranes; geodynamics; temperature; crustal movements; geophysical interpretations; seismic interpretations; seismic waves; p waves; s waves; seismic velocities; anomalies; magnetic interpretations; gravity interpretations; bouguer gravity; tectonic setting; orogenies; deformation; subduction zones; downgoing slab; models; structural analyses; bedrock geology; structural features; folds; faults; shear zones; kimberlites; diamond; Canadian Cordillera; Mackenzie Craton; Mackenzie Fold and Thrust Belt; Cordilleran Deformation Front; Canadian Shield; Wrangellia; Tintina Fault; Laurentia Margin; Intermontane Superterrane; Denali Fault; Mackenzie River Magnetic Anomaly; Slave Craton; Yakutat Block; Liard Transfer Zone; Wrangell Subduction Zone; seismic tomography surveys; high-velocity anomalies; tomographic inversion; mantle flow; structural geometry
Illustrationsgeoscientific sketch maps; location maps; models; cross-sections
ProgramPublic Safety Geoscience, Assessing Earthquake Geohazards
Released2020 01 03
AbstractThe Northern Canadian Cordillera (NCC) is an actively deforming orogenic belt in northwestern Canada. Geochemical and geophysical data show that the NCC is underlain by a thin and hot lithosphere, in contrast with the adjacent cold and thick cratonic lithosphere to the east. This juxtaposition of cold/hot and thick/thin lithosphere across a narrow transition zone has important implications for regional geodynamics. The recent deployment of USArray Transportable Array and other seismic stations across Alaska, USA, and northwestern Canada allows us to image lithosphere and upper mantle three-dimensional seismic velocity structure at significantly improved resolution. Our model reveals a broad high-velocity anomaly across northern Yukon and Northwest Territories, which is interpreted as buried cratonic lithosphere and which we refer to as the Mackenzie craton. Another prominent high-velocity anomaly is imaged beneath northeastern British Columbia and is interpreted to indicate cratonic lithosphere beneath the Northern Rocky Mountains. These two mechanically strong lithospheric blocks, also suggested by regional magnetic data, are interpreted to buttress the ends of the Mackenzie Mountains fold and thrust belt, guiding intervening cordilleran mantle flow toward the Canadian Shield and controlling the arcuate geometry of the Mackenzie Mountains fold and thrust belt. Both P and S wave models also reveal the signature of a northward dipping, subducting Wrangell slab across the southern region of the Alaska/Yukon border. Strong P and S wave velocity contrasts across the Tintina Fault suggest that it is a lithosphere-scale shear zone that extends into the upper mantle beneath the NCC and demarcates distinct regions of lithospheric mantle.
Summary(Plain Language Summary, not published)
The Northern Canadian Cordillera is an actively deforming mountain belt located in the northwestern part of Canada. Previous datasets have demonstrated that this region is underlain by a thin rigid lithospheric plate, and is also quite high in temperature, however, precise estimates of the nature of the crust and mantle across this region have been sparse due to a lack of geophysical infrastructure. In this work, we produce a new high resolution tomography model covering this region, with the intent of more precisely classifying the crust and mantle structures, both in the context of their tectonic evolution, but also their present day thermal state. The thermal state in particular plays a key role in determining the depth extent of ongoing seismicity, as earthquakes are confined to occur only within the cooler, brittle portion of the crust. If the crustal temperatures are truly elevated across this region, the implication may be that earthquakes are confined to occur above the more plastic, higher temperature parts of the crust. Furthermore, this new model, which is regionally more representative of the velocity structure, can be used to derive more accurate local earthquake locations, which will in turn feedback into better understanding of the precise locations of faults and potential hazards.

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