TIMES OF GLOBAL PLATE TECTONIC REORGANIZATION AND THEIR CAUSES

The plate tectonic history of the Earth is the foundation upon which all other components of the Earth System must rest. Since 1985, the PALEOMAP Project has been assembling a global, plate tectonic model that describes the motions of the continents and evolution of the ocean basins during the last 1100 million years. Jurassic, Cretaceous and Cenozoic plate motions are based on linear magnetic anomalies, the tectonic fabric of the ocean floor revealed by satellite altimetry, and the absolute motion trajectories determined by Indian and Atlantic hotspot tracks. Early Mesozoic, Paleozoic and Late Precambrian plate tectonic reconstructions are based on paleomagnetic data, lithologic indicators of climate, biogeographic inferences, and the timing of continental rifts and collisions.

The author has synthesized these diverse and complementary datasets, to produce a global, finite rotation model that describes the movement of over 500 tectonic elements and terranes. This model of Phanerozoic and Proterozoic plate motions permits quantitative estimates of the changes in the plate velocity, and can be used to identify times of major plate reorganization. A preliminary analysis of the PALEOMAP global plate model has identified at least 12 times of global plate reorganization. They are (in millions of years): 1100, 750, 570, 400, 320, 300, 210, 170, 140, 90, 75, 50.

What causes global plate tectonic reorganizations? Numerous authors have suggested that mantle plumes or hotspots may initiate supercontinent breakup. We, however, propose that most significant plate tectonic reorganizations are caused by fundamental changes in plate boundaries that result in new lithospheric stresses. The two principle mechanisms are: continent-continent collision and the progressive subduction of a major oceanic ridge. Plate reconstructions showing the location, or inferred location (pre-Jurassic), of spreading centers, subduction zones, and areas of continental collision will be presented for the 12 time intervals of global plate reorganization.