Unnamed Tectonic Start

[kirkspencer]

This old dog is trying to learn new tricks, and all comments are appreciated.

I'm working on grasping the basics of building a world from (simplified) tectonic movement. To that end, I've put down a start. Plates for which ocean vs continental and motion are identified. And I /think/ I've comfortably identified the convergent, divergent, and transform boundaries.



Now I'm going to be continuing development regardless, so if you'd rather wait and see and point out obvious errors that works as well.

Please note I'm drawing with a mouse, which at this point doesn't bother me given the handwave level at which I'm operating. When I get to actual coasts and other areas where accuracy and control matter I'll drag out other techniques (borrowing heavily on this site's tutorials).

[Mapsburgh]

One thing to keep in mind is that entire plates are rarely all continental or all oceanic. In particular, anywhere there is a divergent boundary, you will end up with oceanic crust on either side of it if it's been going for any length of time.

[kirkspencer]

Thank you, Mapsburgh. I knew about continental plates having ocean on them, but hadn't thought about the other way around.

I've done some tweaking at this level, because when I threw the map above into G. Projector I got:


Needless to say that chaos at the north pole couldn't remain. And I've accidentally learned that doing anything in the north and south margins of that projection is tricksy.

The new map of tectonic plates is better. Not good, just better.

[Charerg]

If I were to do a world map using the tectonics as a starting point (which seems what you're doing), I would start with a supercontinent, then decide how it broke into smaller continents. This will allow you to locate the oceanic ridges (every ocean that is not closing should have one), and also show which continents should have matching shapes. All in all, the key concept in understanding plate tectonics is the Wilson cycle, and the renewal of oceanic crust. I posted a few links which may be useful recently in a similar tectonics-related thread (there's also a fairly detailed tectonics-related post regarding my own con-world, which demonstrates the concept).

Good luck with the project!

[kirkspencer]

Hi Charerg. Your work - and particularly the comments on Deoridhe's Esfera - is in no small part what's been driving me to try this way. Thing is I'm just barely grasping the basic plate movement.

I'm an old fart, I have to take things in small bites these days however much I want to gobble the whole down immediately.

Once I've got a simplistic understanding, the next thing will be trying to figure out how g.plates works. I expect I'll be coming back to you and others here, in particular asking how to figure out where the breakup lines for the supercontinent might plausibly be located.

But thanks for the encouragement.

[kirkspencer]

I'd been told that posts sometimes disappeared while saving. Here I've been waiting for responses.

Charerg, after reading a lot more (yours, Pixie's, Groovey's, Ascanius, and the list goes on) I've decided you're right. I'm going to continue in this thread as a 'lessons learned' for anyone following.

I do have one question given what I've been reading. I'm thinking I want to aim for a dozen 'major' plates out of the supercontinent, with some unknown number of lessers as need and opportunity permit. It looks to me like this is 'realistic' in that repeated reassembly of the supercontinent at the end of several cycles can in turn mean a lot of potential hotspots from which rifts can form.

Am I right in the assumption that the only real problem then is the headache? Or by current understanding of the way things works is there a practical limit on the number of major plates?

[Deoridhe]

Yes, the poles are such a major pain in the butt! I love the idea of starting from a Pangaea, though. I can't wait to see what you make.

[Charerg]

I'd been told that posts sometimes disappeared while saving. Here I've been waiting for responses.

Charerg, after reading a lot more (yours, Pixie's, Groovey's, Ascanius, and the list goes on) I've decided you're right. I'm going to continue in this thread as a 'lessons learned' for anyone following.

I do have one question given what I've been reading. I'm thinking I want to aim for a dozen 'major' plates out of the supercontinent, with some unknown number of lessers as need and opportunity permit. It looks to me like this is 'realistic' in that repeated reassembly of the supercontinent at the end of several cycles can in turn mean a lot of potential hotspots from which rifts can form.

Am I right in the assumption that the only real problem then is the headache? Or by current understanding of the way things works is there a practical limit on the number of major plates?

There is no real limit, but it can be difficult to figure out/justify their movements if you overdo it. Pangaea broke into just 7 seven major plates (NAmerica, SAmerica, Eurasia, Africa, India, Australia and Antarctica). Myself, I think I had something like 9 and it was already a bit of a headache to figure out the movements! This is just including the continental plates (not the purely oceanic plates), but the oceanic stuff can be figured out after the continental movements are clear. So you might want to keep the number of major plates a bit limited.

Regarding the breakup of the supercontinent, a hot spot isn't a necessity for it to occur. The main thing is that you need some "stretching force" to be applied to it. Then the actual location of the rift would depend on a number of factors, such as inherited weaknesses (past orogens are often weaker than the surrounding cratons). I think rifting can even occur in several ways. You can have "passive rifting" with the continents rifting apart accompanied by relatively limited volcanics and "active rifting" with the release of massive flood basalts and associated hotspot activity (Parana-Etendeka, Karoo-Ferrar, North Atlantic Igneous Province, Kerguelen, Ethiopia-Yemen to name some).

It's fairly clear that hot spots do play a large role in continental breakup (though there's also the Siberian Traps which did not result in Eurasia breaking apart). In fact, one theory I read linked the formation of hot spots to the whole Wilson cycle. Given that that the appearance of hotspots at cratonic boundaries during the Pangaea breakup seems to be a bit too convenient to be just a completely random coincidence, this may well be in the right track. The idea is fairly speculative though, given that we still don't understand Earth's inner workings all that well.

One place where hotspot volcanism would be more likely to occur, is if you have a "triple junction" like the Afar Triangle today (btw, tectonic plates never form quad junctions or higher).

[kirkspencer]

So before I get too crazy, here's Debfurkhin - the supercontinent from which everything will develop - up for comment. My questions and remarks after the image.

The only real question is: is Debfurkhin too big? (Or too small). I'm wanting to aim for 25-30% land mass eventually. I recall someone posting a way to check it in Gimp but I've forgotten and am not an expert.

Map notes. I'm expecting to split the continent along the yellow lines. The faint brown lines are hasty orogeny areas, places where I have some older mountains that might be useful later for Irelands and Appalachians and pre-existing rivers such. Spots where you can see the sea are slopping coloring on my part, not lakes.

Split plan. I'm picturing the 2/456 split at start. The next major split will be the 6-14. When I split out the 478 block I also intend to fracture out 1. Question: what time intervals should I be looking at for these splits, or is that one of those "where it looks good to you" situations?

Long term goal: purpose of map. I've got a fantasy world campaign starting in about 6 months and I'd kind of like to use this world for it. I want a largish number of smaller but viable land masses for a couple of reasons. First, because split land masses make it easier to explain divergent humanoids with less "because magic". It's a fantasy campaign, there will be enough of that anyway. Second, I'm leaning toward a bit of nautical (not undersea) background for the game. Having the world justify that by its design helps.

Oh - and I'm not so naive as to think I can have the whole world done. My goal before the six month start point is all continents located with height maps and climatology placed along with major waterways, then detail work of cities and forests and roads and such done where we're going to play for a while.

Knowing that may both aid you in giving advice and inform you in some odd-looking decisions.

[Pixie]

Hi there. I see Charerg has given you the welcome to our very little community of "tectonics weirdos". You're in good hands, but I have to make the customary warning - 99% of the folks attempting this stuff give up.
But you seem to have a plan, so let's flow with it...

I was just reading this the other day: (from this article)
The processes of lithospheric weakening that finally allow continents to break are still poorly understood and geophysical data constraints are sparse. Various ideas exist about the underlying mechanisms that cause continental breakup, ranging from changing plate boundary forces to mantle dynamics.
Which basically says that we still don't know how to explain it, we only know that it happens more commonly where faults already exist. So, you're good to go, and you don't need to worry about hotspots, plumes or whatever. But... you need to understand that the plates will move towards the boundary where they are subducting ocean floor.

With this in mind, instead of deciding the full fracture lines, why not deciding some places where "tear apart pushes" are happening. Small areas, possibly coastal, where the passive margin is transforming into subduction (some scientists think this is hapenning close to Gibraltar these days). You can then set some craton to be pushed in that direction, and another craton pushed in the direction of another subduction zone. Between them, a fracture... and so on and so on. This way you will also be able to force fast rotations and not just plates spreading apart in a linear way.

So, just a suggestion (that you don't need to follow) to exemplify this way of working it out:
- Suppose 11 starts to be pulled by a new subduction in a SE direction...
- ... and that its sutures with 6 and 13 don't crack, so they tend to go SE as well, and the old, weathered mountains with 5 are where the weakness will show up (starting with a horst-grabben system)
- you've got yourself a triple junction between 2, 5 and 6 and another between 5, 13 and 12.
- not yet a rift, but rifting.
- then look at 12. Will it stay behind since it doesn't have much to hold it with the departing 11, which means making it difficult for 13 to follow 11. Or will it yield to the joint pull from 11, push from 13 and the nascent subduction to its SW.
- some million years ahead, as 6 rotates counterclockwise to follow 11, it could create a sort of "tail" to its south (like in Patagonia today), diverting the subduction to the south and away from 2, meaning, plate 2 wouldn't follow for sure, and then you have an opening sea between 2 and 6.
- and so on and so on...
(bear in mind that tectonics don't kick off when the continent breaks up, you need to decide which direction the plates are colliding at your starting point)

My biggest piece of advice though, if you want to break up Debfurkhin and spread it around, is to learn how to use g.plates and learn about Euler Poles (every movement in a planet surface is a rotation... food for thought...). I honestly regret having learnt about this way to late.