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Improved teleseismic Green's functions and western Canada mantle structure and evolution Mercier, Jean-Philippe

Abstract

The present thesis is divided into three distinct parts and focuses both on the improvement of deconvolution technique in a teleseismic context for crustal and upper-mantle studies and on the understanding of western Canada structure and evolution through seismic imaging. The first part presents estimates of the P-component of the teleseismic-P Green's functions for three stations of the Canadian National Seismic Network (CNSN) obtained using a new deconvolution technique. Our results show evidence of the principal, first-order scattered Moho phases and, in particular, the Pp_Mp. The second part presents teleseismic receiver functions from 20 broadband three-component seismometers deployed along the MacKenzie-Liard Highway in Canada's Northwest Territories as part of the joint Lithoprobe-IRIS CAnadian NOrthwest Experiment (CANOE). These stations traverse a Paleoproterozoic suture and subduction zone that has been previously documented in detail to mantle depths using seismic reflection profiling. Our results reveal the response of the ~1.8 Ga subduction zone on both the radial and transverse component. The identification of this structure and its comparison with fine-scale mantle layering below the adjacent Slave province and from a range of Precambrian terranes provides an unambiguous connection between fossil subduction and fine-scale, anisotropic mantle layering found beneath cratons. Previous documentation of similar layering below the adjacent Slave province provides strong support for the thesis that early cratonic blocks were stabilized through processes of shallow subduction. The last part presents P- and S wave velocity models for western Canada. In this part, we focus our attention on two distinct features: 1) the transition from Phanerozoic to cratonic mantle in northwestern Canada and 2) the complex tectonic environment at the northern terminus of the Cascadia subduction zone where the plate boundary changes from convergent to transform. We find that the main transition from Phanerozoic to cratonic mantle in northwestern Canada occurs at the Cordilleran deformation front. In northern Cascadia, we have imaged and characterized the signature of the subducting Juan de Fuca plate and observed evidence of subduction beyond the northern edge of the slab. Our result show that the Anahim hotspot track is underlain by a -2% low-velocity zone.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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