Rifting is the process in which continental crust is extended and thinned, forming extensional sedimentary basins and/or mafic dyke-swarms. Rifts commence as intracratonic, down-thrown blocks dominated by normal or oblique-extensional (transtensional) faults (e.g., the Rhine Graben in Germany and the East African Rift). Rift flanks may be uplifted. Continued rifting results in the break-up of continental plates and creation of oceanic crust (typically 20 to 60 million years after the onset of rifting, but ranging from 7 to 280 million years). Outpouring of flood basalts (also called traps, e.g., the Deccan Traps in western India) can occur over large areas prior to break-up. Marine sedimentary rocks are deposited over the rift sequence during the ensuing phase of post-rift, thermal subsidence.

Rifts commonly develop above upwelling convection cells in the asthenosphere, such as over a mantle plume. Extensional stresses are induced or enhanced by...