Flood basalts, continental breakup and the dispersal of Gondwana: evidence for periodic migration of upwelling mantle flows (plumes)

The present study used igneous provinces, mainly continental flood volcanics or oceanic plateaus, at times as- sociated with regional updoming, major rifting and con- tinental breakup, together with its precisely dated mag- matic events, as indications for paths of plume activity. First-generation plumes - such as the Permo-Carboniferous European-northwest African "EUNWA", and the Jurassic Karoo and Northwest Australia - and convergent environ- ments (Variscan Orogen, the Pacific and the Tethyan subduc- tion zones, respectively) seem to be genetically associated. This may indicate that mantle plumes tend to be initiated by long-lived downwelling lithospheric slabs causing instabili- ties at the lower mantle boundary layers. First-generation plumes are larger (diameter ca. 3000 km) than the late-generation plumes (ca. 2000 km) and appar- ently have a radial dispersion of magmatism and rifting. These plumes ramified spatially and a second generation of plumes, commonly splitting to two offshoots, and even a third generation developed, acting in a similar temporal rhythm ( 60 m.y. plume activity followed by 20 m.y. of quiescence). The Indian path consists of an exceptionally rela- tively short-lasting swarm of plumes: Rajmahal-Kerguelen ( 20 m.y.), Madagascar ( 8 m.y.) and Deccan ( 7 m.y.), whose migration significantly changed course from the main trend. The recurrent consequential breakup and formation of spreading centers along this path is indicative of migration below the upper mantle circulation. This swarm of plumes may also point to a similar Lower mantle source that was influenced by a northeastward weak flow. Although plume migration is suggested to have taken place in the lower mantle, the expansion of magmatism within igneous provinces is probably due to sub-lithospheric migration of the plume.