On the thermal evolution of passive continental margins, thermal depth anomalies, and the Norwegian‐Greenland Sea

Abstract

A computer model of sea floor spreading is presented. This time‐dependent thermal model, which includes the presence of an adjacent continent, simulates not only the evolution of an oceanic region but also the thermal evolution of an Atlantic‐type continental margin. Incorporation of the adjacent continent into a sea floor spreading model allows one to utilize geological and geophysical data from the continent and continental margin as constraints. In terms of the model parameters a more complete picture of the early spreading history and its relation to the initial rifting of the continent is provided. While vertical heat flow dominates in both the ocean and the continent proper, several effects of lateral heat flow across the ocean‐continent boundary are seen. They are reflected in the surface heat flow and topography computed from the model. Owing to lateral heat flow, subsidence of the continental margin can be more rapid than has been estimated from previous models and is a strong function of horizontal position. Applied to the Norwegian‐Greenland Sea, the model satisfies all available geophysical data for that area and produces oceanic depths nearly 1 km shallower than for other oceans of comparable age. It is consistent with the idea that thermal expansion is responsible for the unusually shallow depths and positive free air gravity observed in the Norwegian‐Greenland Sea. These results may be applicable to parts of other oceans where large regions depart from the normal age‐depth curve. Thermal depth anomalies are not necessarily indicative of increased heat input from below but may more generally reflect differences in the ratio of the heat entering the lithosphere to the spreading rate. If it is correct, this concept may provide an origin for some of the shorter‐wavelength relief (10–100 km) seen in oceanic basement. The heat flow distribution across the Norwegian continental margin is consistent with a thermal model in which the Vøring Plateau Escarpment is concident with the ocean‐continent boundary.