Mechanism and sequence of assembly and dispersal of supercontinents

Abstract

The term continent implies a major land mass, with adjacent shelves and possessing one or more internal stable regions known as cratons. In geological time very large land masses had originated as supercontinents and superoceans formed outboard of these. Motions of former cratons and continents have been investigated paleomagnetically and by tectonic tracing. Thus, supercontinents were formed and fragmented in the process of continental drift and ocean spreading. The growth of supercontinents is the consequence of collision with other continents, smaller continental fragments, as well as island arcs, accretionary prisms, and a variety of oceanic plateaux. Dispersal of supercontinents occurred as fragmentation of larger continental masses into smaller blocks took place. There is some evidence that growth and dispersal of supercontinents developed periodically every few hundred million years. The best known relatively young dispersion of a supercontinent is that of Pangea. However, the amalgamation of this supercontinent was more complex and some of its aspects are disputed among those who invoke normal plate tectonic processes and those who suggest the operation of superplumes. The amalgamation of continental fragments occurred by: (i) the development of cold subsiding regions in the mantle; (ii) the adherence of island arcs: or, (iii) the movement of diverse terranes and their collision and accretion to continental masses and those to each other. Several similar scenarios have been suggested in Archean and Proterozoic times. At present Archean plate tectonics are still controversial, but abundant evidence suggests that collisional and accretionary events occurred even then. In the Lower-Middle Proterozoic times amalgamation and accretion became significant, while in the Upper Proterozoic other new cratons originated, possibly by island arc accretion. It is suggested that the break up of continental plates as a consequence of distentional events was prompted by convective changes in the mantle.