Cretaceous-Tertiary geodynamics: a North Atlantic exercise

New reconstructions are presented for the Cretaceous-Early Tertiary North A tlantic using a combination of palaeomagnetic, hotspot and magnetic anomaly data. We utilize these reconstructions in an analysis of previously descri bed misfits between the North Atlantic Plate elements at successive interva ls during this time period. We are able to achieve reasonable overlap betwe en the hotspot and palaeomagnetic reconstructions between 40 and 95 Ma and thus are able to support the idea that the Indo-Atlantic hotspots are relat ively stationary. Small, but systematic discrepancies for this time interva l can readily be modelled with a long-term, octopole non-dipole field contr ibution (G3 = g(3)(0)/g(1)(0) = 0.08). However, hotspot and palaeomagnetic reconstructions for the Early Cretaceous North Atlantic show substantial di fferences that cannot be explained by constant, non-dipole fields and we fa vour an explanation for these discrepancies in terms of true polar wander ( TPW) triggered by mantle instabilities between 125 and 95 Ma; this constitu tes the only identifiable event of significant TPW since the Early Cretaceo us. Taken in the context of available geochronological and geological data and seismic tomography from the region, the 95-40 Ma reconstructions and th eir time-consequent geological products are interpreted in terms of specifi c conditions of mantle-crust coupling and global plate motions/tectonic act ivity. Highlights from these reconstructions show uniform NE movement of th e coupled North American, Greenland and Eurasian plates from 95 to 80 Ma; a marked cusp in the paths for all three elements at 80 Ma where the three p lates simultaneously change direction and follow a uniform NW-directed moti on until c. 20 Ma when Eurasia diverges NE, away from the still-NW-moving G reenland and North American elements. Positioning of the Iceland plume bene ath the spreading-ridge at 20 Ma ma have increased upwelling below the ridg e, increased the ridge-push, and caused a NE shift in the absolute directio n of Eurasia.