Residual geoid anomalies of the North Atlantic Ocean and their tectonic implications

Abstract

Residual geoid undulations of the North Atlantic Ocean are obtained and interpreted in terms of upper mantle processes. Starting from the 1° × 1° averaged Seasat altimeter‐derived geoid, the effects of long‐wavelength features were first removed by subtracting the degree and order 10 geoid of GEM 10C standard earth model. The empirical geoid‐age relationship of the North Atlantic after removing the long‐wavelength features shows closer affinity to the geoid‐age relationship of the plate model than to that of the half‐space model for the older part (greater than 100 m.y.) of the ocean floor. The geoid effects associated with the thermal evolution of the oceanic lithosphere mask the geoid signal associated with deeper processes. We thus removed these effects and compared the resulting geoid with residual depth in order to investigate upper mantle processes. A principal conclusion here is that the axis of the Azores geoid high associated with the Azores triple junction shifts east to Azores Islands after we account for the thermal effects. This may indicate that the main axis of smaller‐scale (upper 600 km) convective upwellings does not lie beneath the present‐day spreading center but beneath the Azores Islands. Further, areas of extensive volcanism such as the Bermuda Rise and Cape Verde Rise in the older part of the ocean floor (ages greater than 100 m.y.) exhibit relative residual geoid highs, which correlate very well with the residual depth anomalies.