HR: 16:15h
AN: S22E-02    [PDF]
TI: Lithosperic strength and current tectonics of the Northern Canadian Cordillera
AU: * Flueck, P
EM: paul.flueck@pfsc.ch
AF: Institute of Geophysics, ETH H”nggerberg, Zurich, 8093 Switzerland
AU: * Flueck, P
EM: paul.flueck@pfsc.ch
AF: Paul Flueck Science & Consulting, Postfach 273, Meiringen, 3860 Switzerland
AU: Hyndman, R D
EM: rhyndman@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada, Sidney, BC V8L 4B2 Canada
AU: Mazzotti, S
EM: mazzotti@pgc.nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada, Sidney, BC V8L 4B2 Canada
AU: Lewis, T
EM: sgc_ltd@bc.sympatico.bc.ca
AF: Sidney Geophysical Consultants, 1107 Maple Road, Sidney, BC V8L 5P5 Canada
AB: Western Canada exhibits large variations 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 Northern Canadian Cordillera is remarkably tectonically and seismically active, extending from this terrane collision zone to the fold and thrust belt at the eastern mountain front. The geodynamics are driven by the Pacific-North America relative plate motion resulting in deformation, seismicity, and mountain building across the whole Northern Canadian Cordillera. Important constraints on the tectonic regime are provide by topography and gravity, estimates of lithosphere thickness and strength, the thermal regime, seismicity, and deformation rates from precision GPS data. 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 over the region using a coherence analysis of Bouguer gravity and topography. There is very thick and strong lithosphere in the old Canadian Shield (T$_{e}$ = 100 km) and thin and weak lithosphere in the Cordillera (T$_{e}$ = 20-30 km). Lithospheric temperatures are the most important control on the strength of the lithosphere, and the depths to the thermally controlled brittle-ductile transition are in general agreement with the T$_{e}$ 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 elevations over thin crust in the Cordillera. In the Canadian Cordillera high temperatures result in 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 is supported by the distribution and rate of seismicity. A 2D finite element mechanical model has been used to model the horizontal strain transfer over a distance of 600-800 km, the development of a lower crust detachment zone, and thrusting at the eastern mountain front.
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
DE: 8122 Dynamics, gravity and tectonics
DE: 8159 Rheology--crust and lithosphere
DE: 9350 North America
SC: Seismology [S]
MN: 2003 Fall Meeting