THE BAHIA-SEAMOUNTS - TEST OF A HOTSPOT MODEL AND A PRELIMINARY SOUTH-AMERICAN LATE CRETACEOUS TO TERTIARY APPARENT POLAR WANDER PATH

Detailed bathymetric and magnetic data collected over the Bahia Seamou nts in the western South Atlantic (Brazil Basin) are analyzed. Six pal eomagnetic poles are determined, one from three seamounts sharing a ri dge, and five from isolated seamounts. Two poles fall near a continent al Late Cretaceous South American pole and are assumed to be of Late C retaceous age. Another seamount has a preliminary Ar-40/Ar-39 age of 6 2 +/- 4 Ma. We check this age and estimate the ages of other seamounts by rotating their poles into North American coordinates and comparing them with North American paleomagnetic reference poles. These ages an d the characteristic magnetic polarities of all Bahia Seamounts are us ed to test hotspot models of formation of the seamount group. The nort hern and central Bahia Seamount chains could have formed from a single hotspot. The southern Bahia chain may require a second hotspot. The t wo postulated hotspots were probably concurrent and separated by 150 t o 200 km. The paleomagnetic poles trace out a smooth curve from the La te Cretaceous poles to a pole that is indistinguishable from the spin axis, which we estimate as having an Early Eocene age. The pole ages r emain preliminary until better age dates are found and rocks are recov ered from more seamounts.