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

Regional maps of lithospheric deformation and thermal history have bee n derived for the eastern continental margin of Canada. Subsidence ass ociated 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-laye r lithospheric extension model was used to compute the deformation and thermal evolution of each region. Deformation results show that the c rust and lower lithosphere have generally stretched by different amoun ts, and that either crustal or subcrustal lithospheric stretching domi nates beneath the various basins. Thermal modelling results for the ol der Nova Scotian and Grand Banks margins show a strong correlation bet ween thermal gradient. crustal stretching, and sediment thickness, and the predicted thermal gradient pattern for the younger Labrador margi n correlates extremely well with predicted stretching of the still-coo ling subcrustal lithosphere. Predictions of sediment maturity (vitrini te reflectance) of basin deposits were obtained from the derived time - temperature histories. Model results have been constrained with obse rvations from individual bore-holes and extrapolated away from these w ell-constrained areas into regions beyond the frontiers of present exp loration. Results are presented as maps showing depths to present-day peak thermal maturity zones and the ages at which earliest postrift se diments 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.