CrustalV_Sstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography

Abstract

Crustal seismic velocity structure in northwest Canada is imaged using group velocity measurements derived from ambient noise cross correlations. The focus area surrounds the Canadian Northwest Experiment (CANOE) array, a 16 month deployment of 59 broadband seismic stations. The CANOE array extended from the Northern Cordillera on the west into the Archean Slave province to the east, crossing crustal terranes that span ∼4 Gyr of Earth history. Forty broadband stations from the Canadian National Seismograph Network and the POLARIS network are also included. The Green's function for each pair of stations is estimated by cross‐correlating 24 h long time series of ambient noise for each day in the time period July 2004 to June 2005. Fundamental mode Rayleigh waves are observed on cross‐correlated vertical component records and Love waves on the transverse components. The group velocity measurements are inverted for 3‐D shear wave velocity within the crust. Local sensitivity kernels are used to account for the effects of a laterally variable sedimentary layer at shallow depths, and receiver function P‐s differential times at the CANOE stations constrain total crustal thickness. Known sedimentary basins dominate lateral variations in wave speed in the shallow crust. In the middle crust, the model contains a strong low‐velocity region that correlates spatially with the location of Proterozoic metasedimentary rocks that have been inferred from active source reflection profiles to occupy much of the crust beneath the Cordilleran terranes. Velocity variations in the lower crust, which are weakly resolved due to the limited period range of our data set (5–20 s), suggest a west‐to‐east transition from lower to higher wave speeds that aligns with the Cordilleran deformation front in parts of the study area. The results presented here are consistent with but do not confirm the notion of Proterozoic strata throughout much of the Cordilleran crust. These metasedimentary rocks, if present, must have experienced some deformation and metamorphism in order to also be consistent with upper mantle seismic models that contain a sharp transition from low to high velocity across the deformation front.

Shear Velocity and Radial Anisotropy beneath Southwestern Canada: Evidence for Crustal Extension and Thick‐Skinned Tectonics

“…In parallel, passive broadband seismic analyses from two permanent Canadian National Seismograph Network stations (EDM and WALA) reveal complex receiver‐side crustal structures based on P ‐to‐ S converted phases (Cassidy, ; Eaton & Cassidy, ), which provide further evidence for plate convergence along the STZ during the Proterozoic Eon. Much of these findings were corroborated by earlier seismic images of the lithospheric structure from temporary arrays deployed in the WCSB, highlighting a first‐order contrast between the Cordillera and the craton (Dalton et al, ) and the presence of the deep cratonic roots beneath the Archean crustal domains (Shragge et al, ).…”

“…Despite relatively few published studies (Bao et al, ; Courtier et al, ; Dalton et al, ; Wu et al, ), western Canada offers a natural laboratory for analyzing continental deformation owing to its protracted tectonic history dating back to three billion years ago (Ross et al, ). The lithosphere beneath this region has sustained major lithospheric deformation, most notably Paleoproterozoic multiplate convergence surrounding the Archean Hearne Province and Phanerozoic orogenesis responsible for the Canadian Cordillera (Figure ; Hoffman, ; Ross, ).…”

3-D geomechanical–numerical model of the contemporary crustal stress state in the Alberta Basin (Canada)

“…The density of the Canadian Shield ranges from 2640 to 2830 kg m −3 , with this model using a value of 2800 kg m −3 . Young's modulus and Poisson's ratio of the basement are calculated based on the V p and V s data from northern Alberta (Dalton et al, 2011). The dynamic Young's modulus and Poisson's ratio (0.21-0.22) are calculated according to Mavko et al (2009).…”

Crustal surface wave velocity structure of the east Albany-Fraser Orogen, Western Australia, from ambient noise recordings

“…However, there are cases where subtle systematic differences in crustal velocities between craton and adjacent orogen have been identified (e.g. Dalton et al 2011).…”