So I've been fiddling around with tectonics some more (because masochism is fun!) and, since misery is much better with company, I wanted to solicit opinions on hypothetical scenarios.

Basically, I'm experimenting with having a "Tethys like" scenario early on during the supercontinent stage (~250 Mya), with a ridge that is destined to be subducted between the northern margin of the ocean between two halves of the supercontinent. When that subduction happens (~225 Mya), the northern margin of the southern continent should rift off and begin heading north. At around the same time--the precise timing doesn't appear to matter all that much--I also have the northern and southern halves of the supercontinent splitting, so a rift exists the entire way between them. Up until now, things seem fine.

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After some time, there should be an oceanic-oceanic margin developing between the "A" and "B" fragments (~175 Mya). My inclination is that B should be subducting under A here as basically a continuation of the margin under the continent, though it also seems feasible that this could be more of a region of diffuse deformation and be more akin to a transform boundary. If either of those options seem wildly incorrect (or wildly correct!), I'd appreciate opinions. Lastly then, when the continental fragment on B collides with A (150 Mya), the question remains with what to do with that same pesky margin; if it's subducting, does subduction cease, or does it instead spread along the continent-ocean passive margin? If it's not, would the two plates basically fuse together? Again, opinions are appreciated

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