TESTING MODELS OF THE TERTIARY PALEOMAGNETIC FIELD

We examine selected paleomagnetic data of Tertiary age in order to assess previously suggested models of the non-dipole portion of the paleomagnetic field. Data from three localities on the African plate (from DSDP Leg 73, ODP Leg 115 and from Gubbio) indicate that the axial octupole contribution was near zero in the Paleocene and was likely no greater than 5-6% of the axial dipole in the Oligocene. Additional data from North America, which can be linked to Africa using well-known relative plate motion parameters, suggest that a positive axial quadrupole field has been present throughout the Tertiary. To investigate some of the practical consequences of these estimates, we apply a non-dipole field model (3 to 4% g2(0)/g1(0), 0% g3(0)/g1(0)) to paleomagnetic data from two ODP sites on the African plate (Sites 710, 711) and from the Deccan Traps. We show that paleomagnetic directions from these deep-sea sediments and from this flood basalt province appear consistent with a fixed hotspot model, suggesting in particular that there has been little or no Cenozoic drift of the Reunion hotspot.