History of the Bahia Seamounts from Geophysical Data

We use geophysical data including magnetic field and gravity measurements and seismic profiles, collected over the Bahia Seamounts, off the coast of Brazil, to construct a history of volcanism for this part of the South American plate. Comparison of paleomagnetic poles from our seamount magnetic anomaly inversions with paleomagnetic poles from South and North America allows us to estimate ages for some seamounts. Radiometric age dates are available for two seamounts. including one for which we found a paleomagnetic pole. The Bahias include many normalpolarity seamounts, some reversed-polarity seamounts, and some mixed-polarity seamounts. Seamounts of like polarity tend to be found together, suggesting a progression of volcanism with time. We fit a hypothetical hotspot track to the seamount ages, magnetic polarities, and trends of the Bahia Seamount chains. We use seamount density and lithospheric flexure models calculated using the gravity data to further constrain the history of volcanism. We model the Bahias with progressive volcanism between about 75 Ma and 50 Ma on 30-40 m.y. old oceanic crust as the South American plate passed over a hotspot that was stationary relative to other South Atlantic hotspots.