Depth and Age in the South Atlantic (Paleoceanographic Mapping Project Progress Report No. 40-0888)
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A significant flattening of the relation between depths and age of ocean floor older than 80 Ma can be explained by assuming that the oceanic lithosphere acts as a thermal boundary layer on top of a viscous upper mantle. In the past, uncertainties of age, of sediment thickness and of bathymetry limited the predictions about this relationship. In this study, recent data from the South Atlantic have been averaged into half by half degree elements, so that the relationship between depth and age can be studied in detail. We constructed a high resolution isochron chart for the South Atlantic using the latest available compilation of magnetic anomaly data and satellite altimetry data. The most recent sediment thickness map is used to correct bathymetry for sediment loading in order to obtain the accurate depth to basement We have plotted the corrected basement depth versus age for the entire South Atlantic as well as for distinct areas. The depth/age relationship is presented as contours about the mode enclosing approximately two thirds of the data. In the South Atlantic, the ocean floor subsides with the square root of age on crust younger than 80 Ma. Beyond 80 Ma depths flatten significantly with age. Moreover, a change of the depth/age relationship for opposite flanks as well as with latitude is obvious, which might be related to small scale convection in the upper mantle.