Geodynamics of continental rift initiation and evolution

Abstract

A continental rift is a nascent plate boundary where the lithosphere is thinned by tectonic activity. Some continental rifts undergo extension to the point that they generate a new ocean basin, whereas others can cease activity altogether. However, the mechanisms that determine rift success or failure remain debated. In this Review, we discuss fundamental rift processes, geodynamic forces and their tectonic interactions and identify the mechanisms that lead to the large variety of rifts on Earth. Rifting initiates through multiscale exploitation of inherited weaknesses, generating dynamic spatiotemporal competition, cessation or localization of rift structures. Progressive thinning of the lithosphere prompts continuous changes in the rift system force balance and prevents a steady-state configuration. Successful continent-scale rifts feature an abrupt and roughly tenfold increase in divergence velocity once the lithosphere is sufficiently weakened. Melt generation during mantle plume impingement can weaken the lithosphere by an order of magnitude, aiding the development of successful rifts. However, at failed rifts, the evolving force balance is dominated by lithospheric strengthening, so that tectonic activity ceases before continental rupture is complete. Outstanding future challenges include unravelling where magmatism is a cause or a consequence of rifting, isolating the tipping points that separate successful from failed rifting and deciphering the interaction of rift tectonics with fluid flow during georesource formation and volatile release. Continental rift zones are regions of crustal extension that manifest through seismic and magmatic activity. This Review explores the variety and development of rifts by assessing their geodynamic drivers, resisting factors and weakening processes.