Everyone here has been super helpful so far, so I wanted to pick your brains about another stage of tectonics that I'm working on to see if what I'm envisioning makes sense as a mechanism. (Apologies if this should be combined with my older thread; if so let me know and I can put it there)

The overall course of the motions is shown in the animation, where the northern supercontinent is traveling south. At some point a change in the tectonics occurs and a triple junction develops between red / blue / yellow; the arm between red and blue either fails or progresses very slowly while the arms involving yellow succeed and lead to the yellow continent breaking off.
rift_4_50Ma.gif

The way I'm currently envisioning the underlying tectonics is detailed in the following few images (standard color scheme of blue = subduction, red = divergent, green = tyransform; coastlines are very rough and island arcs aren't shown). Initially there are three oceanic plates involved, A, B, and C. The driving force for the movement of the supercontinent is the subduction of plate A to the south of the pink continent; B and C are spreading apart with B subducting under the western margins of the supercontinent. Eventually, the spreading ridge subducts under the western edge of the pink continent, resulting in a new westward pull (suction I guess) on pink, which is what initiates the continent breakup. Things then progress with B completely subducting under the continents.

1) stage1.png 2) stage2.png
3) stage3.png 4) stage4.png

My question here is could subduction of a ridge like this reasonably lead to continent breakup in this fashion? Obviously this would also have implications for the rest of C, but I wanted to make sure this part makes sense before worrying about that.

Thanks!