ON THE BREAKUP AND COALESCENCE OF CONTINENTS

Reconstructions of the past positions of the continents indicate that at least twice a supercontinent has formed and subsequently split and dispersed as smaller continents. This has led to speculation about the existence of a periodic cycle of supercontinent coalescence and break up, for which various mechanisms involving mantle dynamics have been p roposed. In this paper we investigate the plate-tectonic system by mea ns of a simple kinematic model to determine to what extent its behavio r results from geometric or kinematic factors as opposed to dynamic pr ocesses. Results from computer simulations show that the overall behav ior of the system is determined by the dimensionless parameter T = Ome ga tau, where Omega is the mean relative angular speed of the continen ts and tau is the mean time interval between plumes. The results for T = 0.10 are in good agreement with observations and indicate that a su percontinent is unlikely to form at current plate speeds in the presen ce of steady-state plume fluxes; evidence of supercontinents therefore implies that plume fluxes and plate speeds have varied through time.