Building Laurentia: evidence from P and S-wave teleseismic tomography and SKS splitting in precambrian northern Canada

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Title: Building Laurentia: evidence from P and S-wave teleseismic tomography and SKS splitting in precambrian northern Canada
Authors: Liddell, Mitchell Vagn
Item Type: Thesis or dissertation
Abstract: The geology of northern Hudson Bay, Canada, spans >3 Ga Earth's history including several Paleoproterozoic orogenies, most notably the Trans-Hudson Orogen (THO). The THO is potentially analogous to the ongoing Himalayan orogen, but whether modern-day-style plate tectonics was responsible is debated. Northern Canada is also an ideal location to study the development of mantle keels: Laurentia's keel underlies both Archean and Proterozoic zones, bringing existing Archean keel-formation hypotheses into question. I explore these issues via teleseismic body-wave tomography and SKS shear-wave splitting analysis of mantle seismic structure. During relative arrival-time analysis, when the network aperture is large (~4000 km), some raypaths retain source-side structure due to subducting oceanic crust and mantle lithosphere waveguides. Mitigation of this source-side influence is essential to avoid travel-time dataset contamination. Final tomographic models reveal complicated internal structure to the Archean Churchill plate and the THO. North-central Hudson Bay is seismically distinct from the THO, consistent with the view that one or more micro-continents were caught between the principle colliders, complicating simple two-plate THO models. Network-wide shear-wave splitting delay times of δt >1 s require a mantle contribution. However, North America has moved too slowly since 50 Ma to create an asthenospheric 'basal drag' anisotropic fabric. Evidence for multi-layered fossil lithospheric anisotropy beneath Archean zones supports episodic development hypotheses for keel formation. Southern Baffin Island is underlain by dipping anisotropic fabrics. When reviewed in light of co-located slow wavespeeds extending north from the Hudson Strait in tomographic models, these data support the view that Paleoproterozoic material underthrust Baffin Island in a modern-style subduction zone setting during the THO.
Content Version: Open Access
Issue Date: Jun-2018
Date Awarded: Nov-2018
Supervisor: Bastow, Ian
Sponsor/Funder: Imperial College London
Department: Earth Science & Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Earth Science and Engineering PhD theses

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