RECONSTRUCTING PALEO-DYNAMIC TOPOGRAPHY OF THE OCEAN BASINS

Dynamic topography results from vertical stresses exerted by mantle flow on the lithosphere. Amplitudes and spatial and temporal scales of dynamic topography are not well known, and direct observations are sparse. Paleo-dynamic topography on the continents is often overprinted by tectonics and is difficult to recognize. In the ocean basins, tectonic overprinting is less of an issue, and signatures of paleo-dynamic topography may have been preserved. We developed a method to reconstruct paleo-dynamic topography from the marine stratigraphic record, and present a test-case of the Somali Basin where paleo dynamic topography resulted from the Afar plume. Several geodynamic modeling studies have predicted the (paleo-) dynamic swell associated with the Afar plume, and we can use those results to compare with our findings.

We reconstruct the paleo carbonate compensation depth (CCD) of the Somali Basin using ODP and DSDP well data, and look for crossings of the seafloor with the paleo CCD. We compare carbonate states in marine stratigraphy on-and off the predicted dynamic swell of the Afar plume to reconstruct dynamic topography amplitude, timing, and dimensions. Careful analysis of carbonate sources from cores are needed to document real carbonate compensation depth crossings of the seafloor.

Our findings suggest that dynamic topography associated with the Afar plume had an amplitude of about 650 m starting prior to 25 Ma at a distance of about 1000 km from present-day Afar. This result is in agreement with recent geodynamic predictions for the Afar swell.