Consider a hypothetical world of the same dimensions as Earth, in which plate speeds are steady at 10 cm/yr, and on which is at one time one mega-continent 6000 km across exists. At time=0 the continent splits in half along a N-S rift extending from the N pole to the S pole, while a subduction zone is simultaneously born along the west edge of the west half of the continent. How long would it take before a major continent-continent collision occurs? (This timescale governs a very long cycle of mega-continent assemblies.)