Are the Pacific and Indo-Atlantic hotspots fixed? Testing the plate circuit through Antarctica

It is often assumed that hotspots are fixed relative to one another and thu s constitute a global reference frame for measuring absolute plate motions and true polar wander. But it has long been known that the best documented hotspot track, the Hawaiian-Emperor chain, is inconsistent with the interna lly coherent tracks left by the Indo-Atlantic hotspots. This inconsistency is due either to unquantified motions within the plate circuit linking the Pacific with other plates, for example, between East and West Antarctica, o r relative motion between the Hawaiian-Emperor and Indo-Atlantic hotspots. Analysis of recent paleomagnetic results from Marie Byrd Land in West Antar ctica confirms that there has been post-100 Ma motion between West Antarcti ca (Marie Byrd Land) and East Antarctica. However, incorporation of this mo tion into the plate circuit does nor account for the Cenozoic hotspot discr epancy. Comparison of an updated inventory of Pacific and non-Pacific paleo magnetic data does not show a significant systematic discrepancy, which, al ong with other observations, indicates that missing plate boundaries and ot her errors in the plate circuit play a relatively small role in the hotspot inconsistency. We conclude that most of the apparent motion between the Ha waiian-Emperor and Indo-Atlantic hotspots is real. The best-estimate averag e drift rate between these sets of hotspots is approximately 25 mm/yr since 65 Ma, ignoring errors in the plate circuit and a small contribution from Cenozoic motions between East and West Antarctica. (C) 1999 Elsevier Scienc e B.V. All rights reserved.