THE EVOLUTION OF CONTINENTAL COLLISION CONTROLLED BY THE WIDTH OF ADJACENT SUBDUCTION ZONE

Continental collision is the major tectonic event that results in supercontinent assembly. Zones of continental collision display some the most rapid and complex deformation patterns, along with high metamorphic grades found in the geological record. At plate boundary scales this deformation is inherently three-dimensional, developing a component as escape tectonics that drives extension of the overriding plate parallel to the plate boundary. Examples of continental collision along the greater Alpine-Himalayan Orogen display a wide variety of deformational and metamorphic responses, indicating that the evolution of continental collision zones is non-unique. Along the Alpine Orogen continental collision was followed by rapid slab-break off, leading to the emplacement of ultra-high pressure metamorphic rocks along the continental suture and quickly ceased convergent deformation. Conversely convergence along the Himalayan Orogen has continued for in excess of 50 Myrs after continental collision, resulting in a minimum of 1500 km underplating and subduction of India beneath Asia during ultra-high temperature, channel flow model, metamorphism. To explain the different types of continental collision zones we use three-dimensional numerical model of continental collision, varying the width of the adjacent subducting slab to control the evolution of convergence. When the continental suture is wider than the resulting adjacent subduction zone, rapid slab break-off occurs with significant post-collision rebound. When the continental suture is less than a third the width of the subsequent adjacent subduction zone, continental collision results in indentation with continued high convergence rates slowly decreasing as the trench becomes increasingly oblique to continental suture. These models display the inherently three-dimensional nature of plate tectonics and continental collision, and the style importance of the wider plate boundary in these tectonic events.