The lithosphere of northwestern Canada recorded more than 2.5 Gy of complex tectonic
evolution, from the formation of the ancient cores of the continental lithosphere such as
the Slave craton to the Phanerozoic Cordilleran orogeny with substantial variations in crust
and upper mantle structures that led to the concentration of natural resources (i.e., diamonds
in cratons). Present-day northwestern Canada juxtaposes a thin and hot Cordilleran
lithosphere to the thick and cold cratonic lithosphere, which has important implications for
regional geodynamics. Recently, seismic station coverage has drastically increased across
northwestern Canada, allowing the development of seismic tomography models and other
passive-source seismic methods at high resolution in order to investigate the tectonic evolution
and dynamics of the lithosphere in this region. The P- and S-wave upper mantle
structures of northwestern Canada reveal that the distribution of kimberlite fields in the
Slave craton correlates with the margin of fast and slow seismic mantle anomalies, which
could delineate weak zones in the lithosphere. Based on our tomographic models we identify
two high-velocity seismic anomalies straddling the arcuate Cordillera Deformation Front
that have controlled its regional deformation, including a newly identified Mackenzie craton
characterized by high seismic velocities extending from the lower crust to the upper mantle
to the north of the Mackenzie Mountains. Furthermore, our P-wave tomography model
shows sharp velocity contrasts beneath the surface trace of the Tintina Fault. Estimates
of seismic anisotropy show a progressive rotation of fast-axis directions when approaching
the fault zone. Together, they provide seismic evidence for the trans-lithospheric nature of
the Tintina Fault. We further propose that the Tintina Fault has chiseled off small pieces
of the Laurentian craton between the Late Cretaceous and the Eocene, which would imply
that large lithospheric-scale shear zones are able to cut through small pieces of refractory
cratonic mantle and transport them over several hundred kilometers.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/41097 |
| Date | 24 September 2020 |
| Creators | Estève, Clément |
| Contributors | Audet, Pascal |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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