Seismic imaging of lithosphere structures of the Western Canada Sedimentary Basin

• Author / Creator

  Chen, Yunfeng

• The Western Canada Sedimentary Basin (WCSB) resides in a transition region from the Precambrian Canadian Shield to the Phanerozoic Cordillera. This broad foreland area has undergone more than three billion years of tectonic evolution from the Paleoproterozoic assembly of the Laurentian craton to the Mesozoic Cordilleran orogenesis along its western margin. This thesis presents updated geophysical imaging results of this tectonically diverse area based on more than a decade (2006-2017) of broadband recordings from dense seismic arrays in western Canada. This unique dataset enables a higher resolution illumination of the 3D seismic structures of the WCSB than previously available, which offers critical constraints on the morphology, composition and evolution history of the lithosphere of the western margin of the North American craton.
  The receiver function imaging reveals increased thickness and Vp/Vs ratio in the crust near the Snowbird Tectonic Zone and the Great Falls Tectonic Zone, two Precambrian discontinuities in the WCSB, which provide compelling evidence for Proterozoic collisions along these boundaries. The finite-frequency travel-time tomography provides high-resolution P- and S-wave velocity models reveals distinct high velocities beneath major Precambrian domains. The lithospheric root beneath the Hearne craton extends down to a minimum depth of 300 km, about 100 km thicker than the surrounding domains. The deep high-velocity root and substantially reduced crustal-shallow mantle velocities beneath the Hearne craton are consistent with earlier tectonic models of the Precambrian assembly. Through an integration of mantle velocity with surface heat flow, isostatic gravity anomaly and kimberlite spatial distribution, this thesis sheds new light on the formation and post-assembly modifications of western Laurentia. Finally, our model reveals a sharp Cordillera-Craton boundary (CCB), which is characterized by large (4.3%) P (7.0% for S) velocity and lithospheric thickness (>200 km) contrasts over a horizontal distance of ~100 km. The CCB dips steeply to the west beneath the southern Rocky Mountain Trench, contrary to a presumed landward-dipping Lithosphere-Asthenosphere boundary. We attribute the CCB to a preserved leading edge of the North American Craton established during its terminal collision with a microcontinent (Cordillera), which provides strong evidence for an upper mantle suture and favors a collisional origin of the southern Canadian Cordillera.

• Subjects / Keywords

  • Western Canada Sedimentary Basin
  • Seismic imaging
  • Craton
  • Finite-Frequency tomography
  • Continental lithosphere
  • Canadian Cordillera

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3MC8RZ0X

• License

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