Microplate and shear zone models for oceanic spreading center reorganizations.

The reorganization of oceanic spreading centers is often accomplished through the process of rift propagation. Examines general rift propagation geometries for the simple 2-plate case in which the propagating rift instantaneously reaches full spreading rate while the other rift dies instantaneously, such that the propagating and dying rifts never overlap. Discusses the more complex geometries that result when both growing and dying rifts spread simultaneously during propagation, such that a tectonically independent overlap region, like the Easter or Juan Fernandez plates along the East Pacific Rise, is produced. Examines the effect of the propagation rate and rise time of spreading on the evolution of overlap regions between dual oceanic spreading centers. Concludes that microplate models offer useful testable hypotheses for describing overlap systems and that shearing need be invoked only to explain features not describable by rigid plate tectonics. Furthermore, the approaches used here to study current overlap regions should be useful in the anlaysis of similar regions formed during past oceanic plate boundary reorganizations.-from Authors