Unnamed Tectonic Start

[kirkspencer]

I sorta get this, but want to run clarification on #1.

I get that B can't subduct the same crust A buried, but what about the crust from the spreading rift developing behind A? Wouldn't that result in a new spreading rift developing behind A at about the end of its plate, and the new plate's boundary being formed by the spreading rift behind B?

(There would be speed and possibly directional changes, but I'm using extreme simplification to focus on my primary question.)

(edited to add quick and ugly map diagram)
Example.png

[Charerg]

If a situation like that occurred, the result would be as follows:

ExampleII.png

In other words, the majority of A would be dragged into plate B due to slab pull. A small piece of A's continental crust might be left behind as an island arc (with a back-arc-basin forming). Perhaps something akin to the situation with the Philippine Sea and Mariana Plates.

[kirkspencer]

Interesting. Not sure I get it so i'll have to do more reading. Regardless, that effect could be fun to pull off somewhere in this exercise. Once.

[Pixie]

Hey! I just burnt over an hour of my life doing a diagram...!

Actually, it's not quite the same as Charerg's, although it ends up with a similar situation. The difference being that I made the intersection happen much earlier and not tearing A apart, but only reversing its motion.
kirkspencer4.jpg

See if you can follow the comic strip and create a legend for it yourself, kirkspencer.

[Charerg]

Yes, Pixie's scenario is the more plausible one, since he takes into account the whole process of how that situation would form in the first place (whereas I simply assumed that the situation *exists* and extrapolated the plate interactions from there).

[kirkspencer]

Thank you both. Pixie's cartoon clarified. But Pixie, am I right to assume the part of Charerg's post for a possible split is correct - the critical requirement being a large enough delay or gap before B forces the rejoining? Alternately a hotspot, but I'm trying to resist arbitrary hotspots as much as I can. It tastes too much like"because (this kind of) magic."

[Pixie]

(...) am I right to assume the part of Charerg's post for a possible split is correct - the critical requirement being a large enough delay or gap before B forces the rejoining?

I suppose it is possible. There isn't much definitive knowledge on rift formation.

Known rifts on Earth have happened on larger continents, though, comparing to the smallish continents A and B of that example. The two active middle-of-continent rifts on Earth in our time are the African Rift and the Lake Baikal rift. One is almost certainly caused (or enhanced) by a mantle plume - the african rift. The other is the result of different blocks of Eurasia moving at slight different velocities and directions - the baikal rift.

If it was up to me, I wouldn't split that continent, but it's a perfectly acceptable solution.

[Charerg]

I suppose it is possible. There isn't much definitive knowledge on rift formation.

Known rifts on Earth have happened on larger continents, though, comparing to the smallish continents A and B of that example. The two active middle-of-continent rifts on Earth in our time are the African Rift and the Lake Baikal rift. One is almost certainly caused (or enhanced) by a mantle plume - the african rift. The other is the result of different blocks of Eurasia moving at slight different velocities and directions - the baikal rift.

If it was up to me, I wouldn't split that continent, but it's a perfectly acceptable solution.

There are also quite a few smaller pieces that have flaked off/relocated due to rifting (Madagascar-India split, Seychelles-India split, Bahamas-Florida split, Yucatan-Mexico split, to name a few). I wouldn't say rift formation is limited to just larger continents (and some of the rifts are quite short-lived), though much depends on the actual structure of the continent (if the continent is just a single cratonic block, the rift would probably form somewhere at the edges of the craton).

Actually, now that I think of it, the Australia-Oceania series of rifting might be the best example, since it seems to have rifted off in similar circumstances (Australian plate being dragged north by slab pull, while at the same time the eastern portion was subducting the Pacific plate, therefore affected by slab suction). See this video for one reconstruction of the process.

Edit:
Actually, the Bahamas-Florida relocation seems to have been a transform fault, not a rift, as a small correction.