THERMOREMANENT MAGNETIZATION OF THE OCEANIC LITHOSPHERE INFERRED FROM A THERMAL EVOLUTION MODEL - IMPLICATIONS FOR THE SOURCE OF MARINE MAGNETIC-ANOMALIES

Thermoremanent magnetization models of the oceanic crust and the uppermost part of the oceanic mantle are derived on the basis of a typical thermal evolution model of the oceanic lithosphere using different magnetic blocking temperature ranges. The magnetization of the basaltic layer 2A has a similar pattern, but with a lower intensity, to that of the standard sea-floor spreading magnetic model; however, the magnetization patterns of the lower crust and upper mantle are skewed, so that in a given polarity period the total magnetization of a lithospheric column which is created early in the period is greater than that of a column which is created later in the period. Magnetic anomalies of the magnetization models are calculated at sea level and at MAGSAT elevation for slow, moderate and fast sea-floor spreading velocities. Although the magnetization models are derived based on purely physical reasoning without using any a-priori information about the observed marine and MAGSAT magnetic anomalies, they do yield magnetic anomalies which are similar to the observed anomalies. The models explain several features of the marine and MAGSAT anomalies. The anomalous skewness of marine magnetic anomalies is explained in terms of the magnetization of the oceanic lower crust. The magnetization of the oceanic upper mantle may account for the anomalous skewness observed over the Cretaceous quiet zones in the Atlantic Ocean. The skewness of the magnetic anomalies calculated at sea level decreases with the increase in the sea-floor spreading velocity.