Episodic growth of continental crust and supercontinents at 2.7, 1.9, and 1.2 Ga may be caused by superevents in the mantle as descending slabs pile up at the 660-km seismic discontinuity and then catastrophically sink into the lower mantle. Superevents, in turn, may comprise three or four events, each of 50-80 My duration, and each of which may reflect slab avalanches at different locations and times along the 660-km discontinuity. Superplume events in the late Paleozoic and Mid-Cretaceous may have been caused by minor slab avalanches as the 660-km discontinuity became more permeable to the passage of slabs with time. The total duration of a superevent cycle decreases with time reflecting the cooling of the mantle.
- Continental crust
- Plate tectonics