EFFECTS OF RIFTING AND SUBSIDENCE ON THERMAL EVOLUTION OF SEDIMENTS IN CANADA EAST-COAST BASINS

Regional maps of lithospheric deformation and thermal history have been derived for the eastern continental margin of Canada. Subsidence associated with the rifting and cooling stages of rifted margin formation was calculated from gridded maps of sediment thickness and bathymetry along the Labrador, Grand Banks, and Nova Scotian margins. A two-layer lithospheric extension model was used to compute the deformation and thermal evolution of each region. Deformation results show that the crust and lower lithosphere have generally stretched by different amounts, and that either crustal or subcrustal lithospheric stretching dominates beneath the various basins. Thermal modelling results for the older Nova Scotian and Grand Banks margins show a strong correlation between thermal gradient. crustal stretching, and sediment thickness, and the predicted thermal gradient pattern for the younger Labrador margin correlates extremely well with predicted stretching of the still-cooling subcrustal lithosphere. Predictions of sediment maturity (vitrinite reflectance) of basin deposits were obtained from the derived time - temperature histories. Model results have been constrained with observations from individual bore-holes and extrapolated away from these well-constrained areas into regions beyond the frontiers of present exploration. Results are presented as maps showing depths to present-day peak thermal maturity zones and the ages at which earliest postrift sediments reached peak maturity levels. This reconnaissance approach has led to predictions of thermal maturity zones suitable for oil or gas generation in western Orphan Basin and beneath the continental slopes.