| In order to characterize the lithospheric structure beneath the Canadian western Superior Province, broadband teleseismic data were recorded along an array that cross-cuts the subprovince boundaries, with an extension into the Trans-Hudson Orogen (THO).; SKS splitting results reveal large splitting times as well as an evolution in fast shear-wave polarization direction when moving northward. The two Trans-Hudson stations show virtually no SKS splitting, in stark contrast with the WSP measurements observed just south.; Three-dimensional traveltime tomography shows significant lateral variations deep into the upper-mantle. The most intriguing is a dipping anomaly that may extend to 670 km. It is uncertain if this represents a paleo-slab that is either frozen since the Archean, recently delaminated from the continental root, or the signature of small-scale convection.; Surface-wave dispersion across the array indicates the presence of a Rayleigh/Love discrepancy suggesting anisotropy is important. Phase-velocity analysis along two orthogonal paths supports the latter idea, as does a close inspection of the Rayleigh/Love particle motions in various frequency bands for various azimuths. Numerical modelling of surface waves using anisotropy layered models mimics the observations with the presence of anomalous surface-wave waveforms as well as azimuthal polarization variations.; Several other observations arise from these data. SKS fast orientation is anomalous at the Wabigoon station 5070, which is also a centre of variable surface-wave polarizations. Similarities are observed between some of my observations and the ones from a collinear refraction survey (Musacchio et al, 2003). Both indicate crustal thinning moving northward, faster E-W upper-mantle velocity and dipping submoho structures. Lastly, although SKS indicates null splitting at the THO station BPW surface-wave polarizations there do provide evidence of significant anisotropy.; This research has highlighted the structural complexity of the WSP. Upper-mantle anisotropy has been widely observed leading to conclusions that the dominant component of seismic anisotropy is located in the continental lithosphere and represents a fossil feature. Heterogeneities have also been identified. In the south, these may be related to the Keweenawan episode, whereas in the central portion of the array they support the existence of Archean subduction processes. |
