Models of plate kinematics along the western margin of the Americas: Cretaceous to present.

Abstract

We provide a realistic assessment of the uncertainties associated with plate reconstructions by creating empirical probability density functions (PDFs) for rotations between plate pairs based upon uncertainties in the positions of observed fracture zone and magnetic anomaly crossings. We determine the PDF for a sequence of rotations through Monte Carlo sampling of the PDFs for these plate pairs. We assign confidence limits within PDFs and find that worst-case uncertainty regions for global reconstruction poles can be twice as large as 95% confidence regions. We illustrate our technique with the anomaly 6 rotation between the Pacific and North American plates and demonstrate that realistic uncertainties for summations of rotations are apt to be significantly smaller than those previously predicted by earlier techniques. We develop revised apparent polar wander paths for the North American and Pacific plates through paleomagnetic Euler pole analysis. We determine motions of the Pacific plate within the hotspot reference frame for the past 80 Ma through a similar analysis and extend the model back to 145 Ma through study of anomalous basement depths and application of the paleomagnetic constraints. The match between the paleomagnetic and hotspot reference frames within uncertainty limits imposed by the available data, contradicts the notion of true polar wander during the late Cretaceous and/or motion between distinct Pacific plates. Applying realistic limits on the expected error in global plate reconstructions, we determine that either the South Atlantic hotspot track is improperly defined, or that there has been more than 1,000 kilometers of relative motion between the Pacific and South Atlantic hotspots since 80 Ma. Our model of plate interactions for the western Americas indicates subduction perpendicular to the margins from 78 Ma to 33 Ma. Northward transpression and transport of allochthonous terranes is limited to regions north of the evolving Pacific-Izanagi (Kula) ridge. We present a series of reconstructions which allows quantification of subduction and lateral transport along the margins. We model the generation of possible oceanic plateaus by known hotspots in the Pacific region and find little evidence to indicate that their subduction had an impact on the magmatic history of North America.