Thermal and mechanical properties of the Cape Verde Rise

Abstract

The Cape Verde Rise represents an extreme case of the process of oceanic midplate volcanism. The regional depth and geoid anomalies relative to the plate model are the largest observed, peaking at 2.4 km and 12m, respectively. The late Tertiary volcanoes rest on Mesozoic‐aged seafloor, indicating that the lithosphere was about 130 m.y. old when loaded. Depth and geoid anomalies in the Cape Verde region are examined using both forward filtering and admittance techniques to determine the thermomechanical properties of the swell. The effective elastic thickness for the plate supporting the volcanoes is 28±4 km and the compensation depth for the broad swell is 69±10 km. These two results, combined with heat flow observations from the rise, are consistent with a model for reheating of the lithosphere beneath Cape Verde such that the average thermal gradient is increased by ∼35%. While there is no doubt that the Cape Verde lithosphere has been reheated, it is unlikely that the entire depth anomaly is explained by thermal anomalies confined to the lithosphere. A linear programming inversion of the geophysical data places an upper bound of 1.7 km on the portion of the depth anomaly due to lithospheric reheating. There are no permissible thermal models fitting all of the geophysical data that do not require either dynamic support from or elevated temperature within the asthenosphere.