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TitleSeismic evidence for craton chiseling and displacement of lithospheric mantle by the Tintina Fault in the northern Canadian Cordillera
AuthorEsteve, C; Audet, P; Schaeffer, A JORCID logo; Schutt, D; Aster, R C; Cubley, J
SourceGeology vol. 48, issue 11, 2020 p. 1120-1125,
Alt SeriesNatural Resources Canada, Contribution Series 20190349
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf; html
ProvinceYukon; Northwest Territories; Nunavut
AreaAlaska; Canada; United States of America
Lat/Long WENS-147.0000 -110.0000 72.0000 58.0000
SubjectsScience and Technology; wave propagation; seismology; anisotropy; Northern Canadian Cordillera
Illustrationslocation maps; graphs; diagrams
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2020 07 21
AbstractThe Northern Canadian Cordillera (NCC), located in northwestern Canada, is juxtaposed to the North American craton and is segmented by several transtensional, margin-parallel, right-lateral strike-slip fault zones such as the Denali and Tintina faults, which have accumulated approximately 430 km of displacement between Late Cretaceous and Eocene. The depth extent of the Tintina Fault has important implications for the tectonic evolution and nature of the lithospheric mantle in the NCC; however, geophysical and geochemical data and models remain inconclusive on this question. Using a high-resolution, three-dimensional P-wave seismic velocity model, we observe a well-defined and sharp P-wave velocity contrast in the uppermost mantle beneath the surface expression of the Tintina Fault. Seismic anisotropy measurements show a clockwise rotation of fast axes of seismic wave propagation and larger delay times (delta-t greater than or equal to 1.5 s) between slow and fast axes in the neighborhood of the Tintina Fault. These data indicate that the Tintina Fault is a lithospheric-scale shear zone. After restoration of 430 km right lateral displacement along the Tintina Fault, a high-velocity P-wave anomaly south of the Tintina Fault becomes aligned with the Mackenzie craton across northern Yukon and Northwest Territories. We propose that this high-velocity P-wave anomaly, which is currently located in eastern Alaska, represents a cratonic fragment that initially belonged to the Mackenzie craton and has been chiseled and displaced to the northwest by the Tintina Fault between Late Cretaceous and Eocene times. These observations suggest, for the first time, that large lithospheric-scale shear zones can cut through refractory mantle and play a major role in displacing lithospheric mantle material in Cordilleras.
Summary(Plain Language Summary, not published)
The Northern Canadian Cordillera is a region of relatively high seismic activity, and separates the well-travelled terranes from the stable Canadian Shield. This complex region is home to a relatively large number of earthquakes (and correspondingly elevated seismic hazard), and several major strike-slip fault systems. In this paper, we use a recently published high-resolution tomography model to look in much more detail at the relative displacement of the Tintina Fault, which is thought to have accommodated roughly ~430 km of right-lateral motion since ~65 million year ago. Reconstructing the mantle structure over this distance aligns a number of anomalies in the lithospheric mantle, demonstrating that the Tintina Fault is likely a lithospheric-scale fault, rather than a shallow crustal fault. This result has significant implications on understanding the larger scale geodynamics of the Northern Canadian Cordillera, and therefore the potential hazard and seismicty that could be expected, both on the Tintina itself, but also other neighbouring faults.

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