Slab gap hypothesis
In
Standard
The slab gap hypothesis proposes that instead of a "window", the descending slab leaves behind a "gap" through which the asthenospheric mantle of the former spreading zone continues to act beneath the overriding plate. This hypothesis then assumes that a crustal spreading zone is also underpinned by a corresponding asthenospheric mantle spreading zone or upwelling of warmer material. The gap is created because instead of the old subducted plate continuing to sink, it quickly melts, allowing the asthenospheric upwelling zone to act directly on the underside of the overriding plate, heating it and causing it to spread apart. The fast melt is because the portion of the subducted plate nearest the spreading zone is thin and still warm from its recent creation.
The slab gap hypothesis goes on to state that the upwelling can form very deep cracks, which in turn lets very fluid basalt lava quickly spread over the land surface forming shield volcanoes and vast volcanic plains called "flood basalts". If, however, the extension is spread over a very large area then these flood basalt events may not occur.
This idea has been used to explain the extension and very large flood basalts that occurred in what is now southern
See also
- Slab window – Type of gap in a subducted oceanic plate