TOPOGRAPHY OF THE OCEAN-FLOOR - THERMAL EVOLUTION OF THE LITHOSPHERE AND INTERACTION OF DEEP MANTLE HETEROGENEITIES WITH THE LITHOSPHERE

Topography associated with large wave‐length geoid is derived by two methods. First, the bathymetry corrected for sediment loading is decomposed using a least‐squares method as a function of age plus terms proportional to the geoid. The topography at old ages is flatter predicted by the law. At degrees 2 and 3, very little topography is associated with the geoid. The transfer function is not even certain in sign but is never smaller than 0.6. More topography seems associated with higher degree harmonics (6 and 7). Second, the function of age alone best fitting the topography is determined. The correlation coefficients of the residual topography with the geoid are then computed. A slight correlation appears for degree 6, but not for degrees 2 and 3. These results suggest a, mechanical decoupling between the lower mantle mass heterogeneities and the lithosphere. Copyright 1990 by the American Geophysical Union.