1. Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
2. Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada

Correspondence to: David W. Eaton¹ Correspondence and requests for materials should be addressed to D.W.E. (Email: deaton@uwo.ca).

Abstract

Since the discovery of plate tectonics, the relative importance of driving forces of plate motion has been debated^{1, 2}. Resolution of this issue has been hindered by uncertainties in estimates of basal traction, which controls the coupling between lithospheric plates and underlying mantle convection^{2, 3, 4}. Hotspot tracks preserve records of past plate motion⁵ and provide markers with which the relative motion between a plate's surface and underlying mantle regions may be examined. Here we show that the 115–140-Myr surface expression of the Great Meteor hotspot track in eastern North America is misaligned with respect to its location at 200 km depth, as inferred from plate-reconstruction models and seismic tomographic studies⁶. The misalignment increases with age and is consistent with westward displacement of the base of the plate relative to its surface, at an average rate of 3.8  1.8 mm yr^-1. Here age-constrained 'piercing points' have enabled direct estimation of relative motion between the surface and underside of a plate. The relative displacement of the base is approximately parallel to seismic fast axes and calculated mantle flow⁷, suggesting that asthenospheric flow may be deforming the lithospheric keel and exerting a driving force on this part of the North American plate.

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