# What happens if continental crust overrides a divergent boundary?

I'm wondering what would happen in this hypothetical scenario. Enjoy these super high-graphic visual representations -

Figure 1 -

Figure 2 -

Figure 3 -

Figure 4 -

What happens to the plate boundaries in figure 4? Would the divergent boundary be erased? Would the red and yellow landmasses stop drifting with no boundary? Would the orange landmass stop at the boundary? Would a subduction zone be formed?

• Would...would,,,would...Would they find the Oak Island treasure underneath? aka you have questions that are purely speculative. Dec 3, 2020 at 21:40
• Is this science based or just fantasy ? Because irl a divergent boundary creates oceanic crust, the scenario is impossible per definition. You can study the concept of a Wilson cycle, continental crust can break up, the orange landmass would then split in two that drift away, with an oceanic ridge in between. Again: Wilson cycle is probably what you're looking for.
– user78828
Dec 3, 2020 at 23:47
• Also, you've constructed something that bears some physical difficulties. There's a destructive boundary just left of the orange mass in mid-blue (or why should it drift about ?) while the other half expands. That's geometrically ... difficult :-) Something's got to give ... there can be a spermwhale and a bowl of petunias ...
– user78828
Dec 4, 2020 at 0:04

• Since the orange continent is moving leftwards, it means that the vertical-ish boundary is a zone of convergence.

• Since the orange continent appears to approach the zone of convergence, it means that the oceanic part of the rightmost plate is subducted under the two leftmost plates.

• Continental crust is lighter than oceanic crust; it has not been observed to subduct under oceanic crust. Which means that once the orange continent reaches the subduction zone, it will float on top, and the two leftmost plates will begin to subduct under the rightmost plate.

• Expect lofty mountains to be raised on the left side of the orange continent. On our Earth, the Rockies and the Andes have been raised in a similar situation.

• The bottom picture is incorrect. The orange continent cannot overshoot the plate boundary. What I would expect is for the plate boundary to remain aligned with the leftmost margin of the orange continent. On our Earth, this is the configuration of South America, which has a subduction zone all along its western margin.

• Ah, okay. So, once the orange landmass reaches divergent boundary, the latter subducts? Do red and yellow reverse direction? Dec 3, 2020 at 21:44
• Why would they? I would expect them to rotate, the yellow clockwise and the red counterclockwise. (Because the right end of the divergent fault will no longer diverge, while the left end will continue to diverge.) Dec 3, 2020 at 21:46
• Okay, think I get it. Thank you Dec 3, 2020 at 21:49

Each land mass is riding on its plate. It is part of the plate.

Yellow and red can ride farther apart as their plates diverge. They are fine.

Orange is cheating I think as it seems to have scooted off the edge of its plate. If the orange plate is ramming into the other two it could uplift land from the other plates (presumably new land would be other colors - maybe puce?) and push orange down, or vice versa.
Orange land should stay on its plate because it is part of the plate. The leading edge of the orange land will probably not have the same shape as the plate it is on collides with those other two plates.

• Ah, sorry. I'll fix the scooting problem Dec 3, 2020 at 21:45
• The question is so speculative we do not know if the black lines represent the edge of plates, lines of volcanos, some form of fault lines, the edges of a liquid pool from the melting blobs, or political boundaries. It really looks like the colored masses are slip-sliding around on some form of one-piece solid rust, like melting ice cubes on a table. Dec 3, 2020 at 21:48
• Plate boundaries can and do cross landmasses.
– user78828
Dec 4, 2020 at 0:01
• a_donda - I agree that 2 plates can meet under a landmass.. I meant only the 3 landmasses depicted here. I do not thank a landmass squarely on a plate should be allowed to scoot off onto another plate. But I am ready to learn - if you have an example of a landmass that "jumped ship" so to speak, link it up! Dec 4, 2020 at 0:02
• Yeah, sorry, I can't imagine that neither. Maybe we should know if it's a fantasy scenario (anything can happen) or not.
– user78828
Dec 4, 2020 at 0:09

What happens to the plate boundaries in figure 4? Would the divergent boundary be erased? Would the red and yellow landmasses stop drifting with no boundary? Would the orange landmass stop at the boundary? Would a subduction zone be formed?

Who knows. The real world setting is convection on a (+/-)sphere, driven by density differences. You have a subduction zone from north to south, or else the orange mass wouldn't drift along. It could split up or just stop in place. The constructive boundary between yellow and red will stop one day (max ~200 million years on present day earth) and subduction will start at the continental margins and the masses start to come together again. Earth history: continents apart - continents together (repeat).

The basic concept is called a "Wilson cycle", part of "modern style" plate tectonics. It all must fit on a sphere and construction in one place means deconstruction elsewhere because planets don't shrink or expand. Things can break, dive down into the mantle, slide upon each other, rotate, transform, slip and thrust, form grabens and whatnot.

For a fantasy scenario, one could consider all these possibilities to fit the story.