Thermal Effects of the Formation of Atlantic Continental Margins by Continental Break up

Abstract

The thermal history of Atlantic continental margins resembles that of the oceanic crust as it spreads away from a mid-oceanic ridge, since the margin was formed when a ridge began spreading beneath a pre-existing continent. During break-up the thickness of the continental crust along the new margin was reduced by subareal erosion and subcrustal processes. Afterwards the continental shelf subsided, probably due to thermal contraction of the lithosphere. The observed subsidence rate on the Atlantic and Gulf coasts of the United States declined exponentially with a time constant of about 50 My, as it does for ridges. Except for the Florida peninsula, deviations of the observed sedimentation from a smooth curve with respect to time could be associated with eustatic changes and variations in the supply of sediments. The subsidence rate of basins in the mid-continent of North America also decreases with a 50 My time constant. In Kansas a subcrustal process must have thinned the crust and initiated subsidence as a sequence of thinly bedded sediments beneath the basin is uneroded.