The hypothesis is that when the spreading zone (the divergent plate boundary) of an oceanic plate is subducted under continental lithosphere[?], then a gap between the two now subducting chucks of oceanic lithosphere[?] forms. Since divergent plate boundaries are fed by mantle plumes[?] the hypothesis is that the mantle plume (which is far larger than a mere hot spot) exploits this gap and causes the overlying continental lithosphere (and the continental crust[?] on top of it) to spread apart.
This idea has been used to explain the extension and very large flood basalts[?] that occurred in what is now southern Washington, Oregon and northern California about 17 million years ago (see Columbia River Plateau[?]). Slab gap has also been used to help explain the earlier creation of the Basin and Range Province.
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