Extraction of a lithospheric cooling signal from oceanwide geoid data

The geoid, an equipotential surface of Earth’s gravity field, reflects the distribution of mass within the planet and hence a variety of geodynamic processes. Because these data are dominated by sublithospheric processes, notably mantle convection, they have not played a major role in the ongoing debate concerning models of the thermal evolution of oceanic lithosphere. Application of spatial filtering to the age derivative of the geoid, however, extracts an age-dependent signal which reflects lithospheric thermal evolution. The data are much better fit by a thin (about 100 km thick) thermal plate than by a cooling halfspace, and so provide a valuable constraint complementary to and consistent with the variations in oceanic depth and heat flow with age.