CONSTRAINTS ON NORTH-AMERICAN PLATE VELOCITY FROM THE YELLOWSTONE HOTSPOT DEFORMATION FIELD

OCEANIC hotspot tracks generally indicate that the mantle plumes that give rise to them are fixed in position (relative to a lower-mantle re ference frame) for timespans of similar to 100 Myr(1-3). It has not be en clear whether continental hotspots are equally stable; for example, there is evidence that the velocity of the Yellowstone hotspot has be en quite irregular with respect to the North American plate over the p ast 16 Myr(4-7), but measurements of its velocity based on caldera loc ations have been too uncertain and irregular to be definitive. Here I describe a new method of obtaining the plume velocity, which uses the broader lithospheric effects of the hotspot rather than the locations of individual calderas. For the past 10 Myr, the results indicate a co nstant North American plate velocity of 2.2 cm yr(-1), which agrees wi th independent estimates from global plate motion inversions(8,9). Thi s velocity is considerably lower than previous estimates obtained from caldera locations, and clearly differs from the much higher (but less well constrained) velocities of the previous 6 Myr (refs 5, 7).