[WIP] World of Aduhr

[Durakken]

I don't like the Agalhaic Plates from your latest map. It looks like you just separated it because you wanted the plates to push in opposite directions. The thing is, from what I can tell is that the equivalent plate on Earth is being subducted on both sides, because there is force of the main ridge is pushing out on the Continental plates which raises above the Oceanic plate. There is 2 small broken off places from the oceanic plate, but those look like they broke due to stress from the shape of the continental plates rather than how you have your split which seems to be there in the center...

Though I do question if this ridge on both sides is possible like in your map, I think it might slow the spread of the continents by at least half, because you're not just pushing over the plate, but the plate is also pushing back at equal speed... and also 2 ridges like that would indicate that the pressure is being released in 2 places which I think would make the process slow as it is... So if it would move at say 4 cm a year on Earth with 1 ridge, your plates I think would have to be reduced as 2 cm due to the double main ridge and then halved again due to pushing back reducing it to 1cm a year... in other words. If you started with Pangea and was headed to our continental structure, instead of 300 million years, it would take 1.2 billion years to achieve. Though like I said, just a thought.

[Charerg]

A quick update:

I was after all inspired by the wealth of input on this thread to do some extra effort and make a (very rough) GPlates model of the plate movements. So far I've roughly drawn the "main pieces" in their present state. I also changed some of the plates to use their "native names" (when I had such figured out). Anyway, this is what the draft looks like at this point:



Next up, I'll try to move the plates around to show their arrangement in the "supercontinent phase". I think I'll decide where to place the (former) Xeteyaric plate as part of that process.

@Pixie: I agree that the Urgaleon-Eocidar border should probably be moved closer to its previous arrangement. I haven't decided what to do with the islands west of Eocidar at this point. One possibility would be to arrange them as a minor continent that is largely submerged, similar to Zealandia on Earth. In that case, they would be a "drifting continent" that wasn't part of the most recent supercontinent but rather had broken off at some earlier point. In this case it would make sense to make the micro-plate they rest upon a part of the East Agalhaic plate. Although I also like your idea about a super-volcano .

@Durakken: The Agalhaic plates closely mirror the Pacific and Nazca plates on Earth. In other words, they're part of a single oceanic plate that has split in two because it is subducted on both sides by continental plates. Speaking of subduction, my understanding is that subduction is actually the main force driving plate movement (and ridges and rifts occur as a result, rather than being the driving force). If you look at Earth, the East Pacific Rise is expanding about 15.1 cm/y at its most expansive point. By comparison, the Atlantic ridge (where bordering plates are subducting rather than being subducted) expands a measly 3.5 cm/y at its most expansive point.

Edit:

@Pixie:I just realised you were talking about the island (almost a micro-continent) east of Eocidar, rather than the western islands. The eastern island (called Dealos) is actually rather important in the grand scheme of things, as it's essentially the "Atlantis" of this world and plays a major role as the land between the major continents. So, I'm definitely keeping that one. As for the geographic explanation, I suppose it's similar to Madagascar (broken off India), a piece of the Nimro-Druegian plate that broke off to join the Eocidarian plate. The sea between Dealos and the Eocidarian mainland can be explained as having been caused by a failed rift. Although there is also a hot spot there that has created the long island chain east of Dealos, and probably the southern portion of the main island as well.

[Durakken]

@Durakken: The Agalhaic plates closely mirror the Pacific and Nazca plates on Earth. In other words, they're part of a single oceanic plate that has split in two because it is subducted on both sides by continental plates. Speaking of subduction, my understanding is that subduction is actually the main force driving plate movement (and ridges and rifts occur as a result, rather than being the driving force). If you look at Earth, the East Pacific Rise is expanding about 15.1 cm/y at its most expansive point. By comparison, the Atlantic ridge (where bordering plates are subducting rather than being subducted) expands a measly 3.5 cm/y at its most expansive point.

As I understand it, this has not been settled, whether it is one way or the other. I can give a guess at explaing the faster movement, but I'm not informed enough there.
The mirroring of the Pacific/Nazca plate; That was my guess. The problem I have with it is that it is too large and doesn't look like it would develop from the shapes. To me, the Nazca plate looks like it was created due to the various stresses created by the other plates, specifically the continental plates where as the Agalhaic plate of your world looks like it isn't informed by anything other than just wanting another plate there that doesn't really do anything.

[Charerg]

Another update:

I finished the "very rough" model of the supercontinent cycle. This and this are the tutorials I used, in case someone is interested.

So, here is the world "150 Million years ago". Note that the timeline isn't that important in this case, this is just a rough approximation. Btw, these images don't include plate names, see my previous post for those.



Some comments:
- I ended up putting Akanrias (formerly the Xeteyarian plate) in the "equatorial supercontinent" as I felt it worked better there.
- There is some overlap between the continents, as the plates are drawn very roughly, and this model doesn't take deformation of the continents (such as the failed rift between Dealos and Eocidar mentioned in my previous post) into account.

100 MYA:


50 MYA:


(See my previous post for "0 MYA")

@Pixie:
Watching through the animated sequence, it becomes clear that (as you suggested) the southern portion of the Valkathain (the inner Ocean) was indeed created at different rates, and that consequently the Nimro-Druegian plate should be split into a Nimrasian plate and a Druegian plate.

As to the seafloor between Akanrias (former Xeteyarian plate) and Nomune, I imagine it as comparable to the Paratethys (of which the Mediterranean and the Black Sea are remnants), an ancient sea in the process of closing.

@Durakken:
Yes, the Agalhaic ridge is indeed intended to have formed as a result of the stresses applied by the surrounding plates. And you're probably right that the eastern portion should be made smaller and split into a few microplates (similar to Nazca, Cocos and Juan de Fuca on Earth). That is, however, a relatively minor detail, and I can fine-tune that plate once I get the "larger picture" right.

EDIT:
@ Pixie: Taking a closer look at the "age of oceanic lithosphere" map, I noticed that there is a weird "triangle" of ancient seafloor in the western Pacific. I don't get why that patch is older than the surrounding seafloor. Any idea why?

2nd EDIT:

I implemented the split of Nimro-Druegia into two pieces. I think the "supercontinent" looks much more plausible now:

[Charerg]

Yet another update. I'll make this a separate post so it's easier to keep track of the progress of the tectonics.

I further refined the model presented in the previous update. Here is what the continents look like during the "supercontinent phase", 150 mya:



Next up, 125 mya, the failed rift between Dealos and Esirmeyr (Eocidar) has formed:


100 mya, the Valkathaic ridge shifts into its final location (this is also when the peninsula of Menduine separates from the supercontinent):


75 mya, the Agalhaic rifts are formed as Akanrias (Xeteyarian) starts subducting beneath Nomune, and Neraduhr moves towards Urgaleon.


50 mya, the south Agalhaic rift shifts, separating the "Misty Isles" from Nomune.


And finally, the present situation, with Urgameyr and Anachain separating from Akanrias:


All in all, I feel this model is plausible and explains the present geography of the planet fairly well. Of course, some finer details like micro-plates still need to be added, but I think that takes care of the "big picture". Any thoughts on this?

Btw, is it possible to "clip" pieces from an imported map in GPlates via defining of the plates and then move them around? I feel seeing the actual geography could be useful and certainly an improvement over the dull line drawings you see in this post.

[Pixie]

Now, I am jealous of your tectonics... Excellent work! The succession of failed rifts and multiple fractures makes it so "realistic". You say it explains "fairly well", but you might as well say it expains "comprehensively".

As for your questions,

- the oldest parts of the Pacific...
If you look at a map of the Pacific, it's very easy to spot a track of volcanic islands west of Hawaii, the further the older, and the oldest are aligned S-N, which means the Pacific was spreading in that direction in the past. Also, I know there was a rift close to Alaska at some time, now covered, this probably explains why the top northern part of the Pacific is younger than immediately to its south...

- clipping pieces of raster images to move with the plates
I don't know if it is possible, but you can draw lines and points in a plate, tag them as any object other than a tectonic plate and explicit to which plate they belong. They will move alongside the plate on the simulations.

[Charerg]

Another update:

I figured out how to clip the imported raster image, and as a result was able to further make the model more "realistic". Here's the final landscape of the planet during the supercontinent phase, 150 mya:


This will definitely make it possible to shape the continental crust in a more "realistic" fashion. Also, I think I'll slightly rework the "tip" of Akanrias, as I am a bit unsatisfied with that particular area, and this gives a nice excuse to adjust the shape.

Also, I realised that GPlates is an excellent way to track "hotspot trails" and added some on the map. This should be useful in reorienting some island chains that I envisioned to be formed via this manner to reflect the plate movements. Here's an image of the planet 50 mya, with most of the hot spots highlighted in red:


And the present day situation (the hotspots are not highlighted in this, but should be pretty easy to spot in most cases):


Once I've updated the map with these slight changes, I'll make a new effort at drawing the present day tectonic boundaries.

EDIT: The attached thumbnail is a slightly outdated version of the 50 mya map, please ignore it. I'm too much of a newbie here to know how to remove a thumbnail .

[Charerg]

So, here is the latest version of the Tectonic layout:



The major change compared to the previous version is in the Agalhaic plate (the "outer Ocean"). As it turned out, due to the movement of the continents the situation actually is a bit different from the Pacific, as the Agalhaic is expanding south- and northwards, while being subducted along its eastern edge (and western, to a lesser extent).

Checking the present layout in 3d, there are a couple of places where the location of the boundaries needs to be shifted (western corner of the "Nomune" plate), but it seems the rifts and the subduction zones are in the right places. Also, since the location of the Agalhaic rift(s) underwent such drastic changes, the orientation of the island chains in the said plate needs to be changed. Fortunately there are only two of those...

So, all in all, aside from a few details, I think I have the tectonic layout in a finished state. Any comments and criticisms are welcome!

Edit:

I fixed the aforementioned "defects" and did a few minor changes as well. Foremost among them I further modified the "Tip of Akanrias", since I wasn't really happy with the previous implementation (I like the new version much better).

[Pixie]

Continues to look good.

Now it's a matter of deciding how much into detail you want to go (obsessive about detail is good, but can consume a whole lifetime ). One area where I'm a little puzzled is the southern side of Rheada. All those islands, is there a rationale behind that, or is it remnant of previous drafts?

Nevertheless, it has reached a pretty functional level of detail - it's now easy to figure where mountain ranges go, where are volcanoes, etc..

[Charerg]

Well, you could say that the islands are a result of previous drafts, as I mimicked the southern side of Indonesia when sculpting the initial forms of the landscape there. Partly it's also a leftover from the original tectonics draft. That said, I think the rationale behind it is sound, since a similarly island-heavy area does exist on Earth at the Australia-Eurasia-Pacific junction. Granted, perhaps I should add more micro-plates there, but they would "functionally" be a part of the larger Rheadan plate (in terms of overall movement direction).

As far as working further at the tectonics, I think the tectonics fulfils it's purpose, as it is intended to serve as "silent information" primarily for the purpose of building the actual topography. So, unless someone has any criticisms or suggestions to offer, I'll probably stick to the present version.

Although I am tempted to add a bit more land to the map, since at present I am at 27,2 % land area, which is a little low compared to 29,1 % for Earth.