Lithosphere mechanical behavior inferred from tidal gravity anomalies: a comparison of Africa and South America

Earlier studies have shown that the amplitude difference of the M2 gravity tidal component (TGA) between the measured and calculated response for a viscoelastic Earth is significantly correlated to the effective elastic thickness (Te) of the lithosphere. Using a regression equation obtained from a global distribution, data from TGA were integrated with those obtained by other methods (gravity-topography coherence and thermo-mechanical analysis) providing a spatial coverage sufficient to establish regional Te patterns for South America and Africa. A comparison and association between the Te distributions for both continents indicates that for the African plate, the effective elastic thickness map clearly shows a remarkable dichotomy of the Neoproterozoic rocks and reworked older rocks. But for the case of South American plate that is moving faster than the African plate, lower Te values are observed only for areas where extensive tectonics with intense volcanism has acted, suggesting that a colder mantle underlies this continental plate, while a hotter asthenosphere is observed beneath the African plate. This is in part attributed to its relatively slow motion which prevented dissipating the earlier developed high temperature.