Hotspot stability and mobility

David Scholl

U.S. Geological Survey

Summary

Paleomagnetic studies carried out on ODP Leg 197, summer of 2001, established that the volcanic edifices of the Emperor Seamounts did not form at the latitude (19.5N) of the Hawaiin hotspot. It can be interpreted that between about 76 and 43 Ma the linear chain of Emperor Seamounts records a southward moving Hawaii hotspot across a generally WNW moving Pacific plate. This interpretation means that the so-called Hawaii-Emperor bend does not record a ~ 40° change (NNW to WNW) in motion of the Pacific plate but rather a great slowing or stoppage of hotspot drift. During the past 43 Myr the hotspot appears to have remained generally fixed with respect to the spin axis.

Discussion

It was remarked that scientists had been aware of the southward drift of the melt anomaly for many years, since biological material dredged from the more northerly Emperor seamounts clearly indicated a colder climate than exists at the present latitude of Hawaii. The apparent southward migration of the melt anomaly up until the time of the bend (of about 800 km), and its cessation at that point raises questions regarding where the deeper part of the conduit would be expected to be, if the volcanic chain were fuelled by a deep mantle plume. If a vertical conduit currently underlies the island of Hawaii, then the conduit must have tilted strongly to the NNW when the Emperor seamount chain began to form. If, on the other hand, the oldest seamount, Meiji, formed when the hypothesised plume was vertical, the plume would now tilt to the SSE and seismic tomography experiments would not be expected to detect it beneath Hawaii.