LATE CRETACEOUS TO EARLY TERTIARY MOTION OF THE HAWAIIAN HOTSPOT AND ITS GEODYNAMIC IMPLICATIONS

The fixed hotspot reference frame underlies a wide range of basic geodynamic concepts including our understanding of the history of plate motions and true polar wander (TPW), the hypothetical rotation of the entire solid Earth with respect to the spin axis. Because of this, the assumptions inherent in the hotspot reference frame can also weigh heavily in the definition of past interactions between oceanic and continental plates, driving mechanisms for terrane transport, and the interpretation of results from paleomagnetic field studies. Recent tests of hotspot fixity utilizing paleomagnetic data from cores obtained by ocean drilling, however, indicate times when groups of hotspots appear to have moved in the mantle at rates comparable to the speeds of some present-day lithospheric plates. One such episode is the Late Cretaceous to Early Tertiary, where paleomagnetic data from Detroit and Suiko Seamounts (Tarduno and Cottrell, 1997) indicate southward motion of the Hawaiian hotspot in the mantle. This motion precludes use of hotspots as a reference frame to calculate TPW, estimates of which may be too large by a factor of 5 when compared with global paleomagnetic data sets (Cottrell and Tarduno, 2000; Tarduno and Smirnov, 2001). To test these conclusions, Ocean Drilling Project Leg 197 recently drilled 4 seamounts of the Emperor trend. At no seamount was a paleolatitude found supporting hotspot fixity. Instead, preliminary data indicate drift rates as great as 50 mm/yr. These data, together with prior paleomagnetic and geochemical results, suggests interaction of the Late Cretaceous Hawaiian hotspot with a ridge axis. This further implies motion of the Pacific plate between 95 and 81 Ma at rates comparable or greater than that of the present day plate. A number of factors could have contributed to a rapid velocity including a relatively small area, large subducting boundary and decreased mantle drag associated with vigorous Late Cretaceous oceanic magmatism.