A geophysical investigation of the lithosphere of the cape verde rise.

The Cape Verde Rise and Islands are considered to be the result of 'Hot Spot' activity. The results of reheating can be observed by changes in the physical properties of the lithosphere. The purpose of this work is to study the relationship of the islands to the rise and relate any changes in the physical properties of the lithosphere to its thermal structure. A geophysical investigation of the lithosphere of the Cape Verde Rise has been carried out using measurements of total magnetic field, seismic reflection profiles, sonobuoy wide angle reflection/refraction experiments, free air gravity and bathymetry from surface ships. Geoid height data from the GE0S3 and SEASAT satellite missions have also been used. Total magnetic field anomalies are attributed to sea floor spreading during the Mesozoic and used to show that 4 fracture zone traces exist in the vicinity of the archipelago. The history of spreading is comparable to corresponding studies in the Western North Atlantic. Seismic stratigraphy from continuous reflection profiles and velocities from wide angle reflection/refraction studies are consistent with uplift during the Early Miocene followed by a period of island building volcanism. Depths to oceanic layer ?, after correction for sediment loading. show that the rise is.;2 km shallower than expected for Mesozoic crust. The present depth is equivalent to only 25 Ma oceanic crust. A 1-dimensional examination of the relationship between free air gravity anomalies and bathymetry using linear transfer function techniques indicates that the lithosphere of the Cape Verde Rise has an effective elastic thickness (EET) of only 15_t3 km when compared with a thin plate flexure model. This value of EET is less than expected for Mesozoic crust from a global compilation of EFT against age of crust at the time of loading. Using geoid height data the above analysis has been extended to 2-dimensions and a value of 13 km has been observed for the EET. The same thin plate flexure model was used for the geoid response as was used for the gravity. The Cape Verde Rise is associated with both a reduction in EFT and a considerable depth anomaly. This is considered to be evidence for thermal rejuvenation. Hawaii, however, is only associated with a depth anomaly and no substantial reduction in EET is observed. This difference between the effect of 'Hot Spot' activity on Hawaii and on the Cape Verde Rise is considered to be due to the motion of the oceanic plate over the mantle heat source