PLUME-SPOTTING: DERIVING THE ABSOLUTE MOTION OF HOTSPOTS AND PLATES

Observed paleomagnetic anomalies interpreted as the result of plume drift has made modeling of absolute plate motions challenging, as direct observations of plume drift are lacking. Plume drift predictions from mantle convection models that broadly satisfy observed paleolatitudes have so far been the only approach to deriving absolute plate motions over moving hotspots. Nevertheless, uncertainties in mantle rheology, temperature, and initial conditions make such models nonunique. By using simulated and real data sets we demonstrate that age progressions along Pacific hotspot trails provide clear constraints on allowable plume motions, and that we can derive models for relative plume drift from these data alone. Relative plume drifts are estimated from the inter-hotspot distances derived from age progressions, but such estimates lack a fixed reference point and azimuthal orientation. Including interpolated paleolatitude histories for the Hawaii and Louisville seamount chains adds further constraints on the plume motions, yet one parameter is unresolved: the longitude offset history that must apply equally to all plumes beneath the Pacific plate. Thus, we can only resolve the motion of hotspots relative to an overall and unknown longitudinal shift as a function of time. Consequently, per Euler’s theorem our computed plate motions are therefore modulated by the same shift via an unknown rotation about the north pole. Plume drift is a consequence of mantle convection; hence, our results place new and strong constraints on the pattern of convection. Other observations, such as geodynamic limits on both plate and plume speeds, the proximity of plumes to LLSVP edges, overall model smoothness, or that the absolute plate motion model produces stable paleo-ridge configurations when tested via “ridge-spotting” may add further constraints that would enable a unique model of Pacific absolute plate and plume motions to be inferred. We strongly recommend the acquisition of additional age and paleomagnetic data, especially from hotspot trails where data are presently lacking, as such data would add critical constraints on both plume and plate motions. Currently, the limiting factor is inconsistencies between sparse paleomagnetic, geometric, and chronologic data, which leads to large uncertainties in the motions.