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Yunfeng Chen Seismic imaging of lithosphere structures of the Western Canada Sedimentary Basin by Yunfeng Chen A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geophysics Department of Physics University of Alberta © Yunfeng Chen, 2018 Abstract 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, ii 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. iii Preface This thesis is an original work by Yunfeng Chen. Chapters 4 of this thesis has been published as: Gu, Y. J., Chen, Y., Dokht, R. M., & Wang, R. (2018). Precambrian tectonic discontinuities in western Laurentia: Broadband seismological perspectives on the Snowbird and Great Falls tectonic zones. Tectonics. I conducted data analysis and contributed to result interpretation and manuscript drafting. Y. J. Gu was the supervisory author developed the original concept and drafted the manuscript. R. M. Dokht and R. Wang contributed to field data collection and manuscript revision. Chapter 5 of this thesis has been published as: Chen, Y., Gu, Y. J., & Hung, S. H. (2017). Finite-frequency P-wave tomography of the Western Canada Sedimentary Basin: Implications for the lithospheric evolution in Western Laurentia. Tectonophysics, 698, 79-90. Chen, Y., Gu, Y. J., & Hung, S. H. (2018). A new appraisal of lithospheric structures of the Cordillera-Craton boundary region in western Canada. Tectonics (accepted). I was responsible for model development and manuscript composition. Y. J. Gu was the supervisory author and was involved with concept formation and assisted with manuscript preparation. S. H. Hung provided the codes for tomographic imaging and contributed to manuscript revision. Chapter 6 of this thesis has been submitted as: Chen, Y., Gu, Y. J., Currie, C. A., Johnston, S. T., Hung, S. H., Schaeffer, A. J., & Audet, P. “Seismic Evidence for a Mantle Suture and Collisional origin for the southern Canadian Cordillera.” Nature Communications (submitted). I was responsible for seismic model iii analysis, idea development and manuscript composition. Y. J. Gu was the supervisory author contributed to the concept formation and assisted with manuscript drafting. C. A. Currie conducted the thermal calculation, interpreted the results and assisted with manuscript drafting. S. T. Johnston provided geological background and contributed to the ribbon continent hypothesis. S. H. Hung provided the tomographic codes and contributed to seismic imaging. A. J. Schaeffer and P. Audet contributed to velocity gradient analysis and manuscript revision. Chapter 7 of this thesis is an original work and is prepared to submit. iv Acknowledgement During the past six years at the University of Alberta, I would not be where I am without the great cares, supports and helps from my colleges, friends and my families. I would like to thank first and foremost my supervisor, Dr. Yu Jeffrey Gu, for his guidance throughout my MSc and Ph.D. studies. To me, Jeff is not only a great mentor but also a lifetime friend whose passion in life and enthusiasm for scientific research will always inspire me. I would like to thank Dr. Shu-Huei Hung from the Taiwan National University. It would not be possible for me to complete my thesis research without her help. I also would like to thank Dr. Claire Currie, Dr. Mauricio Sacchi and Dr. Stephen Johnston for their guidance in various scientific aspects at the UofA, which significantly broaden my scientific interests and horizons in terms of geodynamic, geophysics and geology. I also thank Dr. Larry Heaman and Dr. Carl Tape for their advice and input on my Ph.D. thesis, and thank my collaborator Dr. Qinya Liu, Dr. Andrew Schaeffer and Dr. Pascal Audet for their help on my project. Thanks to all my fellow friends Ramin Dokht, Ruijia Wang, Yuanyin Zhang, Lei Wu, Simon Schneider, Jiayue Shen, Jingchuan Wang, Tianyang Li, Cheng Zhang. It is all of you who make my life at UofA so much enjoyable. Finally, special thanks to my beloved wife and parents for your loves and supports throughout the peaks and valleys of my life. iv Table of Contents Abstract ................................................................................................... ii Preface .................................................................................................... iii Acknowledgement .................................................................................. iv Table of Contents ..................................................................................... v List of Figures .......................................................................................... ix List of Tables ........................................................................................... xv List of Symbols and Abbreviations .......................................................... xvi Chapter 1 Introduction ............................................................................. 1 1.1 Overview .................................................................................................... 1 1.2 Scope of this thesis .................................................................................... 7 1.3 Thesis outline ............................................................................................. 8 Chapter 2 Geological and geophysical overview of regional tectonics ...... 11 2.1 Precambrian summary ................................................................................... 13 2.1.1 Precambrian domains ............................................................................. 13 2.1.2 Snowbird Tectonic Zone (STZ) ................................................................. 18 2.1.3 Great Falls Tectonic Zone (GFTZ) ............................................................ 20 2.1.4 Vulcan Structure (VS) .............................................................................. 21 2.2 Phanerozoic summary .................................................................................... 22 2.2.1 Overview ................................................................................................. 22 2.2.2 Cordilleran belts ...................................................................................... 23 v 2.2.3 Subsurface structures.............................................................................. 25 2.3 Previous seismic studies ................................................................................. 27 2.3.1 Active source surveys .............................................................................. 27 2.3.2 Passive source studies ............................................................................. 30 Chapter 3 Passive seismic imaging techniques ........................................ 33 3.1 Receiver function method .............................................................................. 33 3.1.1 Overview ................................................................................................. 33 3.1.2 Receiver Function processing .................................................................. 37 3.1.3 H-κ Stacking ............................................................................................
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