So I've been fiddling with more temperature-generation-script ideas when I've been up to map-related things recently, but I wanted to resume trying to get Chord right enough to continue with. I set up simulation in GPlates up to 140mya from the present state, and although I'll admit I modeled some things rather roughly (I'm a bit embarrassed, but I started running out of patience with the plate movements ) it gave me a clearer idea of an overall tectonic history/sequence of events to base the current state on.

At ~140mya the major landmasses of Chord are in two supercontinents, one roughly centered on the south pole consisting of what are now F, O, E, V, and A and one roughly on the northern pole consisting of S, M, and C (although F+O+E and V+A are already starting to rift apart). At about this point F+O+E also breaks off a big chunk of oceanic crust from the plate also containing the landmass S - the end result of M+C and F+O+E pulling it in opposite directions. M got the continental crust along with oceanic on the other side (hence now S+M+C).

By 100mya F+O+E and V+A are definitely separate, and F+O continues to be pulled towards M+C+S. E breaks off at this point, although it is moving very slowly compared to F+O (or indeed most of the other landmasses - the plate E is on doesn't really get going too quickly at any point) and it would be probably more accurate to say F+O are broken off of E, even though they have more land area to them. Oceanic crust attached to C+S also starts to get pulled under V+A, and the former will start rifting from M soon as a result. Not too long after this point oceanic crust off the A side of V+A gets broken off by M as well (the 'B' oceanic plate in the image below).

Close to 60mya S rifts away from C under the influence of M; it has a lot of oceanic crust attached to it relative to continental crust which is getting tugged back under M.

Around 40-30mya, F breaks off of O, being subducted under M while O, the slab pull that was causing the F+O versus V+A rifting now only acting on F, begins to have all that oceanic crust that was formed during that long period start to get pulled under V+A again. This is also close to the point where that subduction virus spreads into the M/C ocean and M starts to get pulled back towards C. The very most recent major tectonic event I modeled around ~25mya was the V-A rift, with V getting subducted under E. A doesn't seem to be undergoing any subduction at the moment is is probably moving slower (although at least one plate (O) is being pulled under it).

Realizing I hadn't really modeled oceanic plates all that specifically though, I thought it might be beneficial to throw out a lot of the plate boundaries I'd drawn originally and just mark down what I was more sure about given that history. The result is below (I changed the color scheme to be more along the lines of what you used Charerg - red is divergent, blue is convergent, green is transform and yellow is "I have no clue"). I didn't even draw in some of the boundaries, where I felt really vague about where they should be. Also, where there are convergent boundaries in water I haven't drawn in any formed land, but I will when I draw in more finalized coastlines and islands and so on (such as the tails of V and A where O is pulled under them, like you pointed out Charerg earlier).

chord2plates-reborder.png

There are probably numerous issues in this version too that I haven't even noticed, but there are a few specific points I wanted to ask about:

- What makes sense for plate 'B' (oceanic crust originally attached to A broken off by M)? My thinking was that it was more heavily under the influence of O since M fell under C's influence and O broke from F, but I don't know if this is reasonable. I also don't know how it would be likely to interact with plate A which is now separate from V and also isn't being influenced strongly by M currently. At first I thought it would be pulled back under A, but had the thought that it seemed like that pattern was coming up a lot - oceanic crust formed by rifting, broken off by subduction with other landmass, then pulled back under the original landmass as soon as the situation changes.
- It seems to make sense that that central ocean would be a big oceanic plate, but with the old S-attached oceanic crust involved it looks like a much different situation, and I'm not sure 1) what its border with S would be likely to look like and 2) what its border with the oceanic plate 'T' formerly attached to S (a long time ago) would be doing. It being pulled under the M+F+S group on that side will probably add more livable land area to the present-day S vicinity which is a conceit I found neat all along, though.