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Fluck, Paul, 2003

Contributions to the geodynamics of western Canada

Bibliographic Reference

Fluck, Paul, 2003, Contributions to the geodynamics of western Canada: Victoria, British Columbia, Canada, University of Victoria, Ph.D. dissertation, 332 p.


Western Canada exhibits a large variation in continental lithosphere from very old rocks in the Canadian Shield across the younger Cordillera to the current accretion of the Yakutat Terrane in the Gulf of Alaska. The geodynamics are driven by the Pacific-North America plate motion resulting in deformation, seismicity, and mountain building across the Canadian Cordillera. The way the lithosphere reacts to deformation or loading depends on its thickness and strength. The effective elastic thickness of the lithosphere, Te , has been estimated in this thesis study using a coherence analysis of Bouguer gravity and topography. There is very thick and strong lithosphere in the old Canadian Shield (Te greater than 100 km) and thin and weak lithosphere in the Cordillera (Te = 20-30 km). Lithospheric temperature, derived from surface heat flow and upper crust radioactive heat generation, is the most important control on the strength of the lithosphere. Calculated temperatures at the base of the crust are high in the young and hot Cordillera (~900-1,000 degrees C) and very low in the old and cold Craton (~400-450 degrees C). The depths to the thermally controlled brittle-ductile transition are in general agreement with the Te estimates. The high temperatures in the lower crust and upper mantle of the Cordillera reduce the density by thermal expansion. This thermal isostasy explains the surprising observation of high topography over thin crust. The estimated lithospheric temperatures are used to calculate lithospheric strength profiles. In agreement with the Te estimates, the Cordillera has a weak zone in the lower crust, facilitating detachment of the upper crust. Analysis of GPS continuous and campaign data show that the Northern Cordillera is moving at ~5-10 mm/y in a northward direction driven by the collision of the Yakutat Block in the Gulf of Alaska and is overthrusting the strong lithosphere of the Canadian Shield.*

*This dissertation is multimedia (contains text and other applications not available in printed format). The CD requires the following system applications: Internet Browser; Adobe Acrobat; Microsoft Office.

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