New World (Help with Tectonics?)

[Charerg]

Quick question (I feel like I could make a book out of my 'quick questions' at this point...).

Is it reasonable for the continent in the image to be rifting in two places? My explanation was that the rift formed at A is newer, and is because this piece is moving towards the subduction zone than the other, older rift to the East. The older rift is an eroded collision zone which happened about 100mya, hence the large lakes forming as the two pieces move apart. There is also subduction to the East, further motivating the rift. I don't know if this is too much rifting?

I am trying to understand what the terrain would be like so I can make a reasonably detailed elevation map, taking into account tectonic history and current processes.

Many thanks!

Attachment 106947

If you just want some elevated terrain there, it could also be an aulacogen (an ancient failed rift) or an old collisional orogen as the two pieces collided at some point in the past. I do think two simultaneous rifts along the same axis is a touch unlikely (though not sure if impossible per se, but it would be a fairly short-lived phenomenon).

[davoush]

Thank you Charerg, I will settle with elevated land that is not rifting in that case.

Another question about continental collision & orogeny: Does the 'colliding' continent always produce a plateau on the 'inside' of the concave? I.e. India collides with Tibet, could the Tibetan plateau have occurred on the Indian side of the collision (opposite to what happened)? What if two landmasses are both moving towards each other?

Also, is it reasonable for a mountainous coastline to collide with a continent? I.e. imagine if South America rifted, and the Andes coast was the part colliding with another continent - are there any earth examples of this?

[Charerg]

Thank you Charerg, I will settle with elevated land that is not rifting in that case.

Another question about continental collision & orogeny: Does the 'colliding' continent always produce a plateau on the 'inside' of the concave? I.e. India collides with Tibet, could the Tibetan plateau have occurred on the Indian side of the collision (opposite to what happened)? What if two landmasses are both moving towards each other?

Also, is it reasonable for a mountainous coastline to collide with a continent? I.e. imagine if South America rifted, and the Andes coast was the part colliding with another continent - are there any earth examples of this?

The Tibetan margin was initially a subduction zone like the Andes that pulled the Indian plate towards it, eventually evolving into a continent-continent collision. Similar to Eurasia-Australia convergence, where an island arc-continent collision is taking place in New Guinea (which is an example of a concave orogen). However, you would expect an evolved collision to develop a convex shape at the upthrown side. And no, the Tibetan Plateau couldn't really have formed at the Indian side, as the Indian Plate was the piece being subducted (rather than the other way around).

I am not sure what you mean with a mountainous coastline colliding with a continent. Almost all modern fold belt mountains were initially subduction zones (and typically mountainous) where oceanic crust was being subducted, and evolved into continent-continent collisions as the plate being subducted was pulled towards the trench. I guess you mean if the Andes were to collide with something (with SAmerica being the subducted plate)? Yes, of course that could happen. I guess Northern Africa would be an example, with parts of the Atlas Mountains being originally part of the Central Pangaean Mountains.

[davoush]

Thanks Charerg, I was actually just doing some reading on orogeny and I realized my first question was quite obvious, as of course the subduction zone creates the highland region. I recently found out about foreland basins, so that will be an interesting feature to add in.

Apologies for my unclear second question, yes I essentially meant SAmerica being subducted with the Andes eventually colliding with something.

Also apologies if my questions seem too much - I do often try to read when I get a chance, but a lot of academic papers use specialised terminology which makes it difficult for a non-specialist to grasp easily for amateur purposes. So I very much appreciate your informative answers!

[Charerg]

Also apologies if my questions seem too much - I do often try to read when I get a chance, but a lot of academic papers use specialised terminology which makes it difficult for a non-specialist to grasp easily for amateur purposes. So I very much appreciate your informative answers!

No worries. I can be a bit abrupt at times if I'm writing in a hurry, but being a geology enthusiast of sorts, I kind of like participating in these world building exercises .

Edit:
It may also be helpful/interesting to check the videos over at GeoModels youtube channel. They're basically sandbox experiments that demonstrate geological processes like rifting and fold belt formation. Here's one about the fodl/thrust belt formation.

[davoush]

(Edit: Significantly reworked some sections - see next update. Apologies!)

[davoush]

I think I am getting closer to a tectonic model I am happy with. A goal for this second world was to have more plausible 'motivations' for the current tectonic processes, rather than just jigsaw-ing the pieces together. With that said, here is an updated version. Notably there no longer any polar landmasses.

The main (current) tectonic processes are:

Rifting between A & B, probably started quite a long time ago.

Subduction of H - this is probably a more recent event, maybe after the rift between A & B had become mature. It is subducting with force under A2 - a minor Sunda-style plate.

C collided with B, motivated by the subduction of the southern polar ocean, I. I'm not sure where this would fit on the timeline. I think C will actually be made up of a series of minor plates which have been colliding with B.

F & J: J is an old ocean which is closing, dragging F up with it. There is probably an imminent collision between F and E.

G was probably part of the same ocean as J, and is also closing, causing D to begin rifting from A & E. This is a big East African-style rift originating at the triple junction of A D E.

Some questions:
H is huge. I am thinking of having it also subduct along some other margins. (Maybe into A & E?).

Is it reasonable for C to be made up of a series of 'amalgamated' plates caused by subduction of I? I think C will be in the last phases of collision. I'm not sure which way I is currently moving.

Any other major issues anybody can spot? I will probably add in a few other minor plates, particularly where H is subducting as this is probably very active with lots of volcanic activity and compression of surrounding plates, etc. Also, this world is apparently more or less 80% water, 20 % land which seems like quite little land compared to earth.

Thanks

[Pixie]

Hi, I've been following this, but hadn't had the time/energy to contribute any earlier.. So, as you posted a new version just now, I'll take a stab at it.

Rifting between A & B, probably started quite a long time ago.

This is fine as it is. If you want to justify the rifting between A and B, long time ago, you can imagine B originally having oceanic crust at its SW, which started subducting under an backarc basin roughly north or C's present position. As B moved all the way to that location, subduction inverted which first consumed the backarc basin and then started pulling C (or as many smallish C's you like).

Subduction of H - this is probably a more recent event, maybe after the rift between A & B had become mature. It is subducting with force under A2 - a minor Sunda-style plate.

H may be an ocean composed of mutiple plates, a sort of pacific ocean, with the pacific plate, nazca plate, cocos... Depends on how you choose its movement over at g.plates (you're using g.plates, right?)

F & J: J is an old ocean which is closing, dragging F up with it. There is probably an imminent collision between F and E.

Doesn't look like an old ocean closing. It actually seems to be expanding over plate H, because of the concavity of the tectonic boundary between them. Leaving the boundaries as they are means the crust is being subducted both north and south, by E and F, forcing the existence of a spreading ridge in between. Or, alternatively, ditch the J/F boundary, and everything is being pulled towards E.

G was probably part of the same ocean as J, and is also closing, causing D to begin rifting from A & E. This is a big East African-style rift originating at the triple junction of A D E.

I don't get G, I would need to look at it from a different perspective, maybe a south polar projection. As for the big rift in your largest continent, that's nice as it is (imho).

Some questions:
H is huge. I am thinking of having it also subduct along some other margins. (Maybe into A & E?).

Is it reasonable for C to be made up of a series of 'amalgamated' plates caused by subduction of I? I think C will be in the last phases of collision. I'm not sure which way I is currently moving.

I think I covered these questions with the answers above, but feel free to throw more.
Concerning C, unless you want to go mental on detail, you can decide at your pleasure what stage of collision is it at with B. Here's a picture that you can use as a a-la-carte menu for that..

[davoush]

Thank you very much, Pixie! Of course your keen eye spotted things which I wouldn't have...

As for plate G - in the original G.Plates model, I had the northern half of the 'G ocean' subduct under E - this pulled A into a collision with it, and severed the southern half of G. The movement then changed, and G began subducting towards D. I haven't fulled used G.Plates for this current version and probably won't be able to any time soon, so I am trying to just find reasonable explanations.

I don't mind changing the movements of plates or joining/separating plates to make the current version more plausible, so feel free to suggest anything which looks like it could work.

Looking at it from a south polar projection, perhaps I and G could be joined? I'm not sure which direction of movement would make most sense here, however.

Also, I am unsure about the movement of H in this area. It is generally moving towards B, but perhaps there could be some interesting minor plates in this area, similar to how you mentioned about the Pacific also having some minor Nazca/Coco type plates.

I was also considering an island chain linking D to F somehow, this would mean splitting G into two plates and having a mid oceanic subduction. Too unlikely?

Thanks again!

[Pixie]

Right, so about your plate G.
It's a textbook oceanic plate - spreading ridge close to the south pole, subduction on the opposite margin, which is the boundary with A and D, surely, perhaps a little or all of the G-B boundary. Or, instead of the the G-B boundary, if you rotate G's motion some 45º clockwise, then you have your possible subduction under a chain of islands connecting D and F.
Behind that chain of islands there's several possible configurations: - making the area part of D or part of E, - making it a separate plate slowly moving southwards of E, which includes a small spreading center, - making it two separate plates, one south and one north, ridge in the center and the northern one subducting under E.

Like you said, your south pole projection shows how awkward plate I is presently. You should consider "where" the continental parts of C and F are coming from.. Since they both have oceanic crust on the side closest to each other, maybe they were neighbours in the past along some strip of land that blasted norhwards (that strip of land being the edge of plate G and now long collided with A - of which some remnants transformed into D and are, again, breaking loose).
If this is the case, then the oceanic crust between F and C was/is being produced by their breakup. How back in the past and how quick this happened or is happening is up to you, but it surely got faster when C was pulled against B, as we discussed earlier. And not only it got faster, it might have caused a change in direction (probably).
Where am I heading with this? To the conclusion that the simplest solution is to break I in halves, hand one side to F and the other to C.


Like this... is it readable? (sorry for the horrible scribble, I'm at work, taking a break and using paint)