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Geological Society, London, Special Publications; 2006; v. 268; p. 561-587;
DOI: 10.1144/GSL.SP.2006.268.01.26
© 2006 Geological Society of London

Canadian Cordillera

Ductile thrusting versus channel flow in the southeastern Canadian Cordillera: evolution of a coherent crystalline thrust sheet

Sharon D. Carr1 & Philip S. Simony2

1 Ottawa Carleton Geoscience Centre, Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6 Canada scarr{at}earthsci.carleton.ca
2 Department of Geology and Geophysics, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4, Canada

The Late Cretaceous Gwillim Creek shear zone (GCSZ) exposed in the core of the Valhalla complex, and located in the hinterland of the southern Canadian Rocky Mountain thrust belt, is a 5–7 km thick, easterly verging, ductile thrust zone. It was active after c. 90 Ma and during anatexis (800°C and 800 MPa), rose eastward in the direction of transport, and its base was refrigerated from below at c. 60 Ma by thrust translation onto a cold footwall. Extensional shear zones are younger than the GCSZ, and there is no evidence of channel flow or ductile extrusion. Instead, a 30 km thick, coherent sheet was translated on the GCSZ, which at depth was linked to the Foreland thrust belt such as to form a composite crystalline thrust sheet. Doming of the Valhalla complex may be related to Eocene thrusting beneath the complex during the last stage of shortening. A channel flow, proposed by others for the region north of the Valhalla complex, could have evolved within the crystalline sheet by activation of lateral transition zones and an upper detachment, but is no wider than 250 km, does not represent the dominant orogenic process and may represent a nascent channel.





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L. Godin, D. Grujic, R. D. Law, and M. P. Searle
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[Abstract] [PDF]