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TitleSeismic evidence for lithospheric thinning and heat in the northern Canadian Cordillera
AuthorAudet, P; Currie, C A; Schaeffer, A JORCID logo; Hill, A M
SourceGeophysical Research Letters vol. 46, issue 8, 2019 p. 4249-4257,
Alt SeriesNatural Resources Canada, Contribution Series 20190345
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia; Yukon
NTS94J; 94K; 94L; 94M; 94N; 94O; 95D; 104I; 104M; 104N; 104O; 104P; 105A; 105B; 105C; 105D; 114P; 115A
Lat/Long WENS-136.7500 -122.0000 61.0000 25.0000
Subjectstectonics; geophysics; Nature and Environment; Science and Technology; geophysical surveys; seismic surveys; seismic velocities; seismic waves; seismic data; crustal evolution; crustal thickness; lithosphere; continental crust; mantle; thermal analyses; temperature; Mohorovicic discontinuity; tectonic models; terranes; bedrock geology; structural features; faults; Miocene; Oligocene; Canadian Cordillera; Tintina Fault; Cordilleran Deformation Front; Teslin Fault; Phanerozoic; Cenozoic; Tertiary
Illustrationslocation maps; geoscientific sketch maps; seismic images; profiles; time series; models
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2019 04 15
AbstractGeophysical and geological data indicate that the lithosphere in the northern Canadian Cordillera (NCC) is thin and hot. However, lack of direct constraints on mantle structure is fueling debates on the origin and nature of this lithosphere. Here we image the crust and uppermost mantle beneath the NCC and resolve the Moho at ~35-km depth, the lithosphere?asthenosphere boundary ~15 km deeper, and a westward dipping structure in the mantle below the eastern NCC. We examine end?member tectonic models where the thin lithosphere is either long-lived or has been rejuvenated by gravitational removal. In the long?lived model, steady state thermal calculations indicate a Moho at ~1,000 °C; alternatively, time-dependent calculations suggest that a removal event 5-25 Myr ago reproduces the seismic constraints. Combined with geologic evidence, these results suggest that the mantle lithosphere beneath the NCC is either exotic or the result of progressive thickening and cooling since the Miocene.
Summary(Plain Language Summary, not published)
The lithosphere of the Northern Canadian Cordillera is known to be thin and hot. However, as a result of a lack of dense geophysical instrumentation, precisely how thin and how hot has remained somewhat elusive. In this study, we use data from a profile crossing the southern margin of the Northern Canadian Cordillera to image precisely how thick the crust and lithosphere are, and geodynamically model what implications the observed structure has on the expected thermal regimes. We find that the base of the crust is fairly flat at a depth of ~35 km, and that the underlying lithospheric mantle is very thin, only ~15 km in thickness. Through examination of end member models, we argue that if this thin lithosphere is long-lived, the temperature at the Moho must very hot, ~1000 C. Alternatively, assuming time-dependent transient conditions, a lithospheric-removal event between 5-25 million years ago can satisfy the seismic observations. These high temperatures and thin lithosphere have strong implications on the potential for seismic activity across this region. With very high temperatures, less seismic activity could be expected, as strain can be accommodated through plastic deformation instead of brittle failure.

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