A Reassessment of the Thermal Plate Model for the Ocean Basins

The relationship between the average depth and age of the ocean floor can be approximated using a model of a cooling plate with constant basal temperature in isostatic equilibrium. In previous studies it has been assumed that the thermal conductivity (k), thermal expansivity (α ) and specific heat capacity (c_p) of the lithosphere does not change with temperature (T) and that the temperature under the ridge axis does not change with depth. We use a plate model incorporating laboratory measurements of k(T), α (T) and c_p(T) and an initial temperature structure corresponding to isentropic upwelling with melting, together with information about bathymetry, sediment thickness, sediment density and post-ridge volcanism in the North Pacific and North West Atlantic, to estimate the thickness of the thermal lithosphere under the oceans. We find that a value of approximately 87 km is consistent with both the average variation of unloaded depth with age and the average heat flux beneath the old ocean floor. We then examine the relationship between residual depth anomalies and variations in the intermediate wavelength residual gravity field.