TESTS OF PLATE RECONSTRUCTIONS THAT ASSUME FIXED HOTSPOTS

An important set of plate reconstructions useful for late Mesozoic to early Cenozoic circum-Pacific plate interactions are determined by assuming that the hotspots in the Pacific basin are fixed relative to Indo-Atlantic hotspots. Various studies in recent years have used plate reconstructions and paleomagnetic data to infer rapid motion between hotspots. Recently, for example, some workers have interpreted paleomagnetic results from ocean drilling in terms of rapid southward motion of the Hawaiian hotspot, but their interpretation is based on the unjustifiable assumption that the spin axis is fixed relative to the mantle. Here we present new analyses incorporating new paleomagnetic data and new tools for analyzing plate reconstructions. We find that that little, if any, motion has occurred between Pacific hotspots and Indo-Atlantic hotspots.

Result 1: In marked contrast to the results of several prior studies, we find no significant motion between hotspots for the past 48 Myr for plate reconstructions that use the global plate motion circuit through Antarctica. The upper bound on such motion is about 10 mm/yr. Thus the hotspots unambiguously provide a global reference frame for absolute plate motion for the past 48 Myr.

Result 2: If there have been no "missing" plate boundaries, rapid (≥ 30 mm/yr) apparent motion between Pacific and Indo-Atlantic hotspots from 68 to 48 Ma is required. Alternatively, if the hotspots have been fixed, this motion must be accommodated on a "missing" plate boundary in the global plate circuit between the Pacific plate and the Nubian plate. Our new reconstructions indicate that the required missing motion is small enough to be mainly, if not entirely, accommodated between East and West Antarctica. The best way to distinguish between these two alternatives is with paleomagnetic data.

Result 3: Application of existing and new paleomagnetic data from the Pacific plate and the continents decisively favor a "missing" plate boundary over rapid motion between hotspots.

Result 4: By analyzing paleomagnetic data, we obtain bounds on the motion between Pacific hotspots and Indo-Atlantic hotspots since 125 Ma. We find no significant net motion between Pacific hotspots and Indo-Atlantic hotspots for the past 125 Ma and an upper bound of about 10 mm/yr.

Thus, the motion between Pacific and Indo-Atlantic hotspots has been small.