ISLAND FREEBOARD · What can island isostasy tell us about hotspot dynamics?

Hotspots are enigmatic structures on Earth's surface that are not explained in the framework of plate tectonics. One of the characteristic features of oceanic hotspots is anomalously shallow seafloor, or hotspot swell, on which the volcanic islands associated with hotspots rest. The study of isostatic movements of oceanic volcanoes is a key discriminant among different theories of hotspot swell development. The Cape Verde islands, a hotspot archipelago located in a stationary plate environment, is a particularly good study area because the archipelago is stationary with respect to its melting source, it lies on the largest hotspot bathymetric swell on Earth, and because the archipelago is rich in uplift features. Quaternary wavecut surfaces and marine terraces are ubiquitous in the archipelago and can be found up to ~130 m asl, well above the relevant sea-level maxima. To date, these morphologies remain largely undated but our knowledge on their age is crucial to resolve the mechanisms behind hotspot dynamics. If they are synchronous on different islands they reflect a regional pulse in hotspot swell growth that has not been reported previously. If, conversely, they are not synchronous between islands, they require local uplift mechanisms (e.g. basal intrusions), also not previously documented. We propose an innovative multi-disciplinary approach to date the Quaternary uplift features of Cape Verde using state-of-the-art multi-nuclide surface exposure dating of wavecut surfaces in combination with U/Th Disequilibrium geochronology of marine terraces. The information will provide an uplift chronology that will be used to test competing hotspot swell development models and hotspot theories