1. Prediction of Emperor-Hawaii seamount locations from a revised model of global plate motion and mantle flow Steinberger, R., Sutherland R., and O’Connell, R.J.

2. Problem: Global plate motion reconstructions do not properly predict the bend (~47Ma) in the Emperor-Hawaii seamount chain location Solution: Model the movement of hotspot plumes and combine the results with new global plate reconstructions until a closer fit is obtained

3. Hotspot Motion Modeling A large scale mantle flow field was determined from the mantle’s density structure which is inferred from: 1) seismic tomography 2) global plate motions 3) radial mantle viscosity structure Temporal variations in the mantle flow field were computed from plate motions The velocity of points along the plume conduit were computed as the vector sum of ambient mantle flow and a buoyant rising velocity The motion of plume conduits is controlled by the viscosity structure of the mantle where: high viscosity lower mantle – advection dominates low viscosity upper mantle – buoyancy dominates The Hawaiian plume is moving faster than its reference counterparts because it is helped by large scale upwelling

4. N-S cross section of the mantle at 155º a) 120 Ma; b) 90 Ma; c) 60 Ma, d) 30 Ma Plume initiation: red-170 Ma, purple-150 Ma

5. Plate Motion Reconstructions and Hotspot Tracks Four Hotspots tracks were used to model plate motions with two hotspots on each plate to separately determine plate motions relative to hotspots in either hemisphere Tristan and Reunion hotspots on the African Plate Hawaii and Louisville hotspots on the Pacific Plate All assumed to have a deep mantle origin, necessary for the model to work For plate motion reconstructions, relative plate motions can be described by observations of the sea floor in the South Pacific and southern Indian Ocean Motion between the plates is known for some times, but not all Any intraplate deformations in Antarctica and/or New Zealand cannot be quantified Two separate plate motion chain models were used to: 1) see if hot spot motion alone can predict the bend in the Emperor- Hawaii seamount chains, and if not 2) constrain the locations and magnitudes of intraplate deformation

6. Model 1 Africa East Antarctica West Antarctica New Zealand Pacific Model 2 Africa East Antarctica Australia New Zealand Pacific

7. For plate motion chain models 1 and 2, the predicted tracks of the Louisville, Tristan and Reunion hotspots match the observed results.

8. Model 1 - Results Hotspot motion is sufficient to explain any discrepancies between predicted and observed hotspot tracks up to 47 Ma However, before ~47 Ma, predicted hotspot tracks do not include the bend in the Hawaiian-Emperor chain and is too far west The difference cannot be reasonably accounted for by altering hotspot motion Model 1 Red Line

9. Model 2 Blue Line Model 2 - Results Hotspot motion is sufficient to explain any discrepancies between predicted and observed hotspot tracks up to 47 Ma From 83-52 Ma the prediction of the northerly direction of the Emperor seamount chain is better but before 65Ma is still west of the chain

10. Summary To properly predict plate motions via hot spot tracks it is important to consider hotspot motions in the mantle and intraplate deformation. Neither model provides a perfect fit without considering intraplate deformation. The difference between the predicted hotspot tracks between 47 and 65 Ma is attributed to intraplate deformation within Antarctica. The divergence of the predicted hotspot track before 65 Ma is possibly due to intraplate deformation in New Zealand. However, hotspot tracks cannot be explained by intraplate deformation alone because of unreasonable tectonics.