Testing the fixed hotspot hypothesis using Ar-40/Ar-39 age progressions along seamount trails

Hotspots and their associated intra-plate volcanism producing seamount trai ls have become an accepted fact in geology from a conceptual theory. The az imuths and age progressions of these seamount trails provide the only means to determine absolute plate motions with respect to an independent referen ce frame of 'fixed' hotspots. However, the presumed fixity of hotspots is i n disagreement with recent paleomagnetic studies and global-circuit plate r econstructions for the Hawaiian-Emperor seamount trail. In this study, we p rovide independent evidence suggesting that hotspots are not fixed relative to each other. We use a straightforward test that compares the observed Ar -40/Ar-39 age progressions along Pacific seamount trails (0-140 Myr) with t he Pacific plate velocities as predicted by their poles of plate rotation ( i.e. Euler poles), In most of these comparisons, the age progressions were found incompatible with published Euler poles, or with a new set of Euler p oles as derived in this study using discrete seamount locations digitized f rom the bathymetry maps of Smith and Sandwell [EOS 77 (1996) 315; Science 2 77 (1997) 1956-1921]. We conclude that the relative motion between hotspots may be required to reconcile the observed age progressions with the predic ted plate velocities from their modeled Euler poles. On average, the Pacifi c hotspots may show motion at 10-60 mm/yr over the last 100 Myr, partly att ributed to individual hotspot motion, whereas systematic motion of these ho tspots (due to true polar wander) may account for the remainder. (C) 2001 E lsevier Science B.V. All rights reserved.