ANIMATION OF PLATE MOTIONS AND GLOBAL PLATE BOUNDARY EVOLUTION SINCE THE LATE PRECAMBRIAN

A computer animation will be presented that illustrates both plate motions and the evolution of plate boundaries since the Late Precambrian. Plate motions during the Jurassic, Cretaceous and Cenozoic plate motions are based on linear magnetic anomalies and the tectonic fabric of the ocean floor revealed by satellite altimetry, in combination with “absolute” motion trajectories determined by the Indian and Atlantic hotspot tracks and paleomagnetism. Early Mesozoic, Paleozoic and Late Precambrian plate tectonic reconstructions, however, are less well constrained and are based on less precise paleomagnetic data, lithologic indicators of climate, biogeographic inferences, and the timing of continental rifts and collisions. In addition to the motion of the plates, the animation shows the continuous evolution of global plate boundaries. Though the rifts and subduction zones associated with the breakup of Pangea are well known, the pre-Mesozoic plate boundaries shown here are speculative. Their location is based on the timing of rifts and continental collisions inferred from the geologic record, and the fundamental assumption that plates move as a result of slab pull and ridge push. For example, fast moving plates must be attached to old, cold subducting slabs. Large continental plates (Eurasia), on the other hand, tend to move slowly because of deep lithospheric keels. The evolving geometry of plate boundaries controls the tempo and mode of plate evolution. The history of plate motions might be best described as “long periods of boredom, interrupted by short intervals of terror (rapid change)”. Episodes of global plate reorganization punctuate long periods of steady-state plate motion. As shown by the animation, these global reorganizations are due to catastrophic changes in plate boundary geometry that result in new lithospheric stress regimes. One of the most important plate boundary events is the subduction of a spreading center. The subduction of the Tethyan Ridge in the early Jurassic may have been responsible for the breakup of Pangea.