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UBC Theses and Dissertations

Teleseismic investigation of the upper mantle beneath the Archean Slave craton, NW Canada, and of the Moho beneath Canadian broad-band stations Bank, Carl-Georg

Abstract

In this thesis I apply various algorithmic techniques to teleseismic data with a twofold objective: to investigate upper mantle structure beneath the Archean Slave craton to gain an understanding of early craton formation and kimberlite genesis, and to characterize elastic properties, including anisotropy, at Moho levels beneath Canadian seismic stations. The Archean Slave craton is the site of the oldest known rocks on Earth and of numerous diamondiferous kimberlites. The Yellowknife seismic array and 13 temporary stations recorded teleseisms between November 1996 and May 1998. P-wave travel-time tomography reveals the oldest part of the craton, the Central Slave Basement Complex, to be underlain by the fastest seismic velocities. Receiver function analysis requires only the Moho as a major 5-wave velocity discontinuity and points to a fairly constant crustal thickness throughout the craton. SKS splitting analysis shows little variation in results across the array, supporting present-day plate motion as the primary cause for mantle fabric beneath the area. Furthermore, the Mackenzie plume seems to not have had any seismologically detectable effect on the Slave lithosphere. I speculate on a genetic link between a low seismic velocity anomaly at depth with the overlying Lac de Gras kimberlite field. To characterize elastic properties at Moho levels beneath Canadian broadband stations I use the Moho P-to-5 converted phase in the P-coda, and linearized scattering theory combined with singular value decomposition. I first identify those parameter combinations to which idealized teleseismic data sets are most sensitive. Five independent parameter combinations are potentially resolvable, one of which is sensitive to isotropy whereas the remainder quantify different harmonic orders (19 and 29) of back-azimuthal response. I then use these parameter combinations to compare Moho anisotropy at 25 sites. The isotropic component dominates at all stations and corresponds to shear velocity contrasts across the Moho ranging between 10 and 35 percent. Perturbations to anisotropic material property parameters are more modest, generally between 3 and 7 percent when consistent between SV and SH responses, and in many cases suggest an anisotropic lower crust. Inconsistent responses may manifest contamination by lateral heterogeneity, upper crustal reverberations, or pervasive crustal anisotropy leading to shear-wave splitting.

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