EPISODIC CONTINENTAL GROWTH AND SUPERCONTINENTS - A MANTLE AVALANCHE CONNECTION

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 sl abs pile up at the 660-km seismic discontinuity and then catastrophica lly sink into the lower mantle. Superevents, in turn, may comprise thr ee or four events, each of 50-80 My duration, and each of which may re flect slab avalanches at different locations and times along the 660-k m discontinuity. Superplume events in the late Paleozoic and Mid-Creta ceous may have been caused by minor slab avalanches as the 660-km disc ontinuity became more permeable to the passage of slabs with time. The total duration of a superevent cycle decreases with time reflecting t he cooling of the mantle. (C) 1998 Elsevier Science B.V. All rights re served.