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The AAPG/Datapages Combined Publications Database

CSPG Bulletin

Abstract


Bulletin of Canadian Petroleum Geology
Vol. 38 (1990), No. 1. (March), Pages 169-169

C.S.P.G. 1990 Convention, "Basin Perspectives"

Crustal Structure and Geodynamic Models for the South Jeanne D'Arc Basin, Offshore Eastern Canada [Abstract]

Keen, C.E.1, Reid, I.1, Boutilier, R.1

ABSTRACT

The Grand Banks area, offshore eastern Canada, contains several deep half-grabens that were formed by extensional forces during Mesozoic rifting of the North American plate with respect to Africa, Iberia and Europe. While we understand these plate tectonic motions that led to rifting, we do not understand how the lithosphere deformed under extension to produce these basins, and other Triassic-Jurassic half-grabens of this type in northeastern North America. In order to investigate the lithospheric and deep crustal controls on basin development, deep crustal reflection and refraction seismic studies have been undertaken across the south Jeanne d'Arc Basin. Results show that Moho is almost flat beneath the basin, and that most of the crustal extension may have been accommodated by the basin-bounding fault, which extends into the lower crust but does not appear to cut the Moho. Extension in the lower lithosphere may have been via penetrative flow. A distinct lower crustal layer, with a velocity of 7.2 km/s, is observed and is interpreted as supporting evidence for rift-related magmatic intrusion and/or underplating of the crust in the vicinity of the basin. These results were used to constrain geodynamic models of the extension of the lithosphere. Models of the lithosphere include a layered, temperature-dependent rheology, conduction and advection of heat, and isostacy. A "fault" or pre-existing zone of weakness is incorporated in the crust and this localizes deformation. The progressive deformation of the lithosphere is computed from the onset of rifting. Results of modelling are compared with observed deep structure, and with the shape and generalized stratigraphy of the basin. These models provide a good fit to the observations, and are more powerful than earlier models in that they give a physically meaningful representation of lithospheric deformation both during and after rifting. The results show that the mode of deformation is more complex than earlier kinematic "pure" and "simple" shear models would suggest. This additional complexity will affect the heat input and therefore the thermal maturity predicted for the sediments.

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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES

1 Geological Survey of Canada, Dartmouth B2Y 4A2

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