Theory 72/Wilson cycle/Termination phase
Closure Needs a Density Threshold
The claim
An ocean closes when the ratio of slab density to mantle density exceeds one, because subduction becomes the only path.
01Mechanism
Dense oceanic lithosphere sinks; the ratio determines whether it can.
02Prediction
Closure should track the density ratio.
03Refutation
Closure tracking convergence would remove buoyancy.